How are single socket spurs adequately protected on a 32A ring?
David Robinson
to protect the cable to the fitting, and the fuse in the plug is
supposed to protect the cable to the appliance, how is the single bit
of 2.5mm T+E run to a single socket spur adequately protected by
anything?
You've basically got 2 bits of 2.5mm in parallel (usually unequal
lengths), feeding a single bit of 2.5mm. 32A MCB.
Whereas if it was a standard radial circuit, you'd have just the
single bit of 2.5mm, and you'd only be allowed a 20A MCB on it. (IIRC
they even dropped the 2.5mm rating down to 18A, which is "correct" in
accordance with the calculations, but then increased it back to 20A
because that's what everyone does anyway).
I'm not worried. I just don't see the logic.
I have 10cm of 2.5mm T+E protected by a 40A MCB on the cooker circuit
(feeding a socket that can only supply the gas hob ignition) and that
seems very wrong too - but wiring a socket in 6mm is just too painful.
However, the cooker circuit may yet drop back to 32A (because I
suspect that's all it needs) which makes it no worse than the socket
spur discussed above.
?
Cheers,
David.
Tim Watts
Fuse in the plug at max of 13A.
Odd as it may seem, overload protection *can* exist downstream as well
as upstream.
In the case or a short circuit in the back of the socket, the 32A
breaker will still protect the cable (ie interrupt the current before
the cable overheats).
--
Tim Watts
ARWadsworth
The short version -
You have to consider the difference between overcurrent protection and fault
protection.
If an MCB is used for overcurrent protection then the circuit has to be
capable of running at the full current allowed by the MCB. For a B type MCB
this is 1.45 times the rating of the MCB.
If the MCB is to be used only for fault current protection (ie a short
circuit) then the cable only needs to be able to pass the short circuit
current long enough to allow the MCB to trip within the required times when
there is a fault.
A ring from 2.5 T&E is capable of meeting the 32 x 1.45 current overload
protection that a B type MCB provides.
Now a spur from a ring is "self" overcurrent protecting as is is only
allowed to feed 1 single socket or 1 double socket. The maximum normal
current that you get down this spur is 26A (assuming a double socket loaded
to the maximum) which is less than the 27A capacity of 2.5 T&E when clipped
direct (or buried in plaster) so there is no overcurrent problem and the MCB
is now only needed for short circuit protection to protect the spur.
However if there is a short on the spur (nail, angle grinder etc) then the
resistance reading at the end of the spur must be low enough to trip the MCB
in the times required for a short circuit. The resistance reading is made up
from the supply impedance plus the cable impedance, so the longer the length
of the spur the greater the chance that the spur is not compliant and may
not clear a short in the required time.
--
Cheers
Adam
David Robinson
Thanks Tim.
So on a 20A radial, the 20A is to protect against overloads (lots of
"up to 13A" loads, potentially causing damage over time without ever
tripping a 32A) whereas a short circuit would generate enough current
to trip a 32A before the cable suffered harm?
Where can I find that calculation? I saw those MCB and fuse trip-time
vs current graphs the posted the other week, but can't remember
reading a shot circuit disconnect time requirement.
Do I need to change my 40A to a 32A, or leave it as it is?
Cheers,
David.
David Robinson
wrote:
brilliantly clear - thanks Adam.
Cheers,
David.
ARWadsworth
NO. A 20 radial is a circuit with a 20A MCB. A spur from a 32A ring is a
different thing. ( my other post did not make that one clear)
> Where can I find that calculation? I saw those MCB and fuse trip-time
> vs current graphs the posted the other week, but can't remember
> reading a shot circuit disconnect time requirement.
http://wiki.diyfaq.org.uk/index.php?title=Fuse
for the graphs.
> Do I need to change my 40A to a 32A, or leave it as it is?
I would change it. Far easier than doing calculations. However I would not
use the 2.5 T&E for use with an electric cooker without making some very
accurate calculations.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:G5aOo.31783$ol5....@newsfe06.ams2...
>
>> Do I need to change my 40A to a 32A, or leave it as it is?
>
> I would change it. Far easier than doing calculations. However I would not
> use the 2.5 T&E for use with an electric cooker without making some very
> accurate calculations.
Its self protecting exactly as a spur on a 32A ring is (it only has a single
13 socket).
I would change it too, most electricians would reject it as they don't know
how to do the calculations and its just easier to use the regs than to
explain why its OK.
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:G5aOo.31783$ol5....@newsfe06.ams2...
>
>>
>>> Do I need to change my 40A to a 32A, or leave it as it is?
>>
>> I would change it. Far easier than doing calculations. However I
>> would not use the 2.5 T&E for use with an electric cooker without
>> making some very accurate calculations.
>
> Its self protecting exactly as a spur on a 32A ring is (it only has a
> single 13 socket).
Yes it is at the moment, but it will not be if the OP installs an electric
cooker, and he has hinted that he may do so.
> I would change it too, most electricians would reject it as they
> don't know how to do the calculations and its just easier to use the
> regs than to explain why its OK.
(the regs tell you what is OK and they give you the calculations, the regs
and what is OK are inclusive not exclusive)
I have to take the bigger view. I might be able to show that a certain
cooker is safe when installed with the 2.5 T&E, however the customer may
change the cooker for a higher powered one or sell the house and a new owner
may fit a higher powered cooker. I would rather see a cooker circuit
correctly fused to the actual cable rating and not to some diversity
calculations that mean nothing when a cooker is swapped.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:mIaOo.3887$ju7....@newsfe10.ams2...
> dennis@home <den...@killspam.kicks-ass.net> wrote:
>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>> news:G5aOo.31783$ol5....@newsfe06.ams2...
>>
>>>
>>>> Do I need to change my 40A to a 32A, or leave it as it is?
>>>
>>> I would change it. Far easier than doing calculations. However I
>>> would not use the 2.5 T&E for use with an electric cooker without
>>> making some very accurate calculations.
>>
>> Its self protecting exactly as a spur on a 32A ring is (it only has a
>> single 13 socket).
>
> Yes it is at the moment, but it will not be if the OP installs an electric
> cooker, and he has hinted that he may do so.
>
>> I would change it too, most electricians would reject it as they
>> don't know how to do the calculations and its just easier to use the
>> regs than to explain why its OK.
>
> (the regs tell you what is OK and they give you the calculations, the regs
> and what is OK are inclusive not exclusive)
You can do anything you like if you are competent to do the calcs, I believe
that's in the regs somewhere.
The majority of electricians mean the onsite guide when they refer to the
regs.
>
> I have to take the bigger view. I might be able to show that a certain
> cooker is safe when installed with the 2.5 T&E, however the customer may
> change the cooker for a higher powered one or sell the house and a new
> owner may fit a higher powered cooker. I would rather see a cooker circuit
> correctly fused to the actual cable rating and not to some diversity
> calculations that mean nothing when a cooker is swapped.
That I agree with.. diversity is a PITA.
It doesn't even work when someone swaps a few single plugs for doubles in a
ring and then plugs in a few fan heaters at one end.
That sort of things makes rings run out of spec.
I suppose its regarded as unlikely that some will use 9kW of heating in a
room, even one they are trying to dry out after the recent floods. ;-)
ARWadsworth
>>> I would change it too, most electricians would reject it as they
>>> don't know how to do the calculations and its just easier to use the
>>> regs than to explain why its OK.
>>
>> (the regs tell you what is OK and they give you the calculations,
>> the regs and what is OK are inclusive not exclusive)
>
> You can do anything you like if you are competent to do the calcs, I
> believe that's in the regs somewhere.
> The majority of electricians mean the onsite guide when they refer to
> the regs.
The same rules and regs apply to both the full BS7671 and the OSG.
>> I have to take the bigger view. I might be able to show that a
>> certain cooker is safe when installed with the 2.5 T&E, however the
>> customer may change the cooker for a higher powered one or sell the
>> house and a new owner may fit a higher powered cooker. I would
>> rather see a cooker circuit correctly fused to the actual cable
>> rating and not to some diversity calculations that mean nothing when
>> a cooker is swapped.
>
> That I agree with.. diversity is a PITA.
> It doesn't even work when someone swaps a few single plugs for
> doubles in a ring and then plugs in a few fan heaters at one end.
That makes no difference in most cases. Most people do not have a massive
store of fan heaters ready to be used.
> That sort of things makes rings run out of spec.
For a short time that will not matter.
> I suppose its regarded as unlikely that some will use 9kW of heating
> in a room, even one they are trying to dry out after the recent
> floods. ;-)
But you know damn well the correct tool is a dehumidifer not a heater for
this job.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:RjbOo.35739$sA4....@newsfe28.ams2...
>> I suppose its regarded as unlikely that some will use 9kW of heating
>> in a room, even one they are trying to dry out after the recent
>> floods. ;-)
>
> But you know damn well the correct tool is a dehumidifer not a heater for
> this job.
OK, 9 kW of heating + 1kW of dehumidifier.
ARWadsworth
But that never happens. I doubt that three 3kW fan heaters will stay on for
long if they are in the same room. They have thermostats.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:JJbOo.10669$EO....@newsfe25.ams2...
The problem being that there is no way to know, it might be a big room with
the doors and windows open with a gale blowing through, they would stay on
then.
The reason why I brought it up is because I have seen it happen BTW.
Not everyone would think about running an extension lead from somewhere else
to make sure there wasn't a problem. They would leave it running until the
room was dry or it all failed.
ARWadsworth
You are missing one important point.
Ring mains are designed for normal domestic use not for clearing floods.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:secOo.61839$QU2....@newsfe14.ams2...
> You are missing one important point.
>
> Ring mains are designed for normal domestic use not for clearing floods.
Shame that very few know that it can be dangerous, something that could be
designed out.
ARWadsworth
The IET must be stupid. Why did they not let you design the new regs for
them?
--
Adam
John Rumm
> In a bout of man flu, I lay in bed wondering: If the MCB is supposed
> to protect the cable to the fitting, and the fuse in the plug is
> supposed to protect the cable to the appliance, how is the single bit
> of 2.5mm T+E run to a single socket spur adequately protected by
> anything?
This is one of those occasions where the responsibility for overload
protection and fault protection can be split. The fault protection (i.e.
very high short circuit currents) must always be at the origin of the
circuit, however the overload protection can be at the load end in some
cases. (others would include a 3A drop wire to a pendent fixing on a 6A
protected lighting circuit for example - the largest bulb you can get
won't come close to 3A so no chance of overload))
An unfused spur can power a total of one double or single socket. The
diverse load of a double socket is taken as being 20A. (That is lower
than the current carrying capacity of 2.5mm^2 T&E in all but the most
adverse installation methods). Even the theoretically possible 26A is
just under the maximum rating when clipped direct or buried in masonry.
So the conditions at the load end (i.e. only one double socket)
enforce the overload protection.
The next question concerns the fault protection. i.e. what happens when
you nail through the cable or some other drastic fault occurs. Here you
will get a fault current that limited only by the the resistance of the
wires themselves and that of the supply and earth connections. This is
one of the reasons for their being a maximum cable length specified for
most circuits - to ensure the so called "Earth Loop Impedance" (i.e.
round trip resistance from supply through circuit wires, and to earth)
can't get too high.
A 32A breaker will typically need as much as 160A to open "instantly"
i.e. on the magnetic part of its trip response. Instant in this case
means 0.1 secs or less.
See charts here:
http://wiki.diyfaq.org.uk/index.php?title=MCB#Types_B.2CC.2CD
Lets say you work out that your prospective fault current is going to be
200A, you now need to assess[1] what happens when you try and stick that
down the skimpy 1.5mm^2 earth wire. Needless to say that will get hot,
and quickly. Its also going to be heating so fast that the natural heat
losses to its surroundings are going to be negligible during the time
scale we are interested in. So we have what can be though of as
adiabatic heating.
What you need to check is that it won't melt before its done its job and
tripped the MCB. For this you use what is called the adiabatic equation:
s = sqrt( I^2 x t ) / k, where s = the minimum cross sectional area of
copper required in the conductor, and k is a factor specific to the the
type of cable (115 in the case of PVC T&E).
So 200A, a check of the MCB charts says this is plenty to open the
breaker in 0.1 secs. So our sum becomes s = ( 200 x 200 x 0.1 ) / 115 =
0.56mm^2, which is significantly less than the 1.5mm^2 we actually have
an hence is ok.
[1] In reality you can skip this stage since these are "standard"
circuit designs where as long as you obay the length limits, you know
the design "works".
> You've basically got 2 bits of 2.5mm in parallel (usually unequal
> lengths), feeding a single bit of 2.5mm. 32A MCB.
>
> Whereas if it was a standard radial circuit, you'd have just the
> single bit of 2.5mm, and you'd only be allowed a 20A MCB on it. (IIRC
> they even dropped the 2.5mm rating down to 18A, which is "correct" in
> accordance with the calculations, but then increased it back to 20A
> because that's what everyone does anyway).
Current carrying capacities are listed here:
http://wiki.diyfaq.org.uk/index.php?title=Cables#T.26E
> I'm not worried. I just don't see the logic.
>
>
> I have 10cm of 2.5mm T+E protected by a 40A MCB on the cooker circuit
> (feeding a socket that can only supply the gas hob ignition) and that
> seems very wrong too - but wiring a socket in 6mm is just too painful.
Well the overload protection is achieved by the 13A maximum load on the
socket. The only other question is will it be adequately fault
protected. Assuming the rest of the circuit is a more substantial cable,
the the loop impedance ought to be fairly low to that point. Hence it
seems reasonable to assume you will get fault current in excess of
200A. That will open the 40A circuit breaker in 0.1 secs, and we know
from the sum above that the wire will handle it.
> However, the cooker circuit may yet drop back to 32A (because I
> suspect that's all it needs) which makes it no worse than the socket
> spur discussed above.
Indeed. In fact due to the nature of the load presented by cookers, even
a very powerful cooker with a theoretical peak load over 60A will
usually be fine on a 32A circuit. (cooker diversity is calculated as 10A
plus 30% of the remainder). So a 60A cooker would need a circuit
provisioned for 10A + 0.3 x 50 = 25A, or 30A if there is also a socket
on the cooker point.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:YscOo.49417$N41....@newsfe23.ams2...
So you don't think they got the compromise between cost and safety on ring
mains wrong then?
That would be why they added radials with breakers that actually match the
cables because they didn't need to.
Who knows, sometime in the future when all the old electricians have retired
rings will finally die.
Tim Watts
>
>
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:YscOo.49417$N41....@newsfe23.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>> news:secOo.61839$QU2....@newsfe14.ams2...
>>>
>>>> You are missing one important point.
>>>>
>>>> Ring mains are designed for normal domestic use not for clearing
>>>> floods.
>>>
>>> Shame that very few know that it can be dangerous, something that
>>> could be designed out.
>>
>>
>> The IET must be stupid. Why did they not let you design the new regs
>> for them?
>
> So you don't think they got the compromise between cost and safety on
> ring mains wrong then?
> That would be why they added radials with breakers that actually match
> the cables because they didn't need to.
> Who knows, sometime in the future when all the old electricians have
> retired rings will finally die.
Rings have notable safety benefits over radials, namely that the CPC is
doubled up over two paths.
Also, show me a practical 32A radial with multiple socket drops noting
the BS standard restrictions on terminal capacities of socket and FCU
accessories.
--
Tim Watts
dennis@home
"Tim Watts" <t...@dionic.net> wrote in message
news:iecln6$rf5$1...@news.eternal-september.org...
> Rings have notable safety benefits over radials, namely that the CPC is
> doubled up over two paths.
They also have several safety problems.
They can have latent faults that the householder will only find out about
when its too late.
Things like broken earths (which negates your above argument) can just be
there undetected for years unless you have regular inspections and real
continuity tests.
This isn't a solution though as the act of doing the test will make the
faults more likely to occur.
>
> Also, show me a practical 32A radial with multiple socket drops noting the
> BS standard restrictions on terminal capacities of socket and FCU
> accessories.
Why do you need a 32A radial?
I don't think you will find them in the OSG.
4mm will do the job with many accessories and you could always crimp in a
joint if the accessory is to small. I wouldn't bother with a 32A radial to
replace a ring.
Tim Watts
>
>
> "Tim Watts" <t...@dionic.net> wrote in message
> news:iecln6$rf5$1...@news.eternal-september.org...
>
>> Rings have notable safety benefits over radials, namely that the CPC
>> is doubled up over two paths.
>
> They also have several safety problems.
> They can have latent faults that the householder will only find out
> about when its too late.
> Things like broken earths (which negates your above argument) can just
> be there undetected for years unless you have regular inspections and
> real continuity tests.
> This isn't a solution though as the act of doing the test will make the
> faults more likely to occur.
>
>>
>> Also, show me a practical 32A radial with multiple socket drops noting
>> the BS standard restrictions on terminal capacities of socket and FCU
>> accessories.
>
> Why do you need a 32A radial?
Because 20A is fuck all use to me.
I do not want to be thinking - are these sockets on the same 20A circuit
- damn I cannot plug this 3kW appliance in because there are already two
high load appliances on that circuit.
I already also have enough RCBOs in my CU - I don't have space for even
more, let alone the expense.
> I don't think you will find them in the OSG.
Bugger the OSG, it is a guide only. I think you WILL find them in
Appendix 15 of the 17th.
> 4mm will do the job with many accessories
4mm doesn't cut it for Reference Method B (a common installation method
in my house).
> and you could always crimp in
> a joint if the accessory is to small. I wouldn't bother with a 32A
> radial to replace a ring.
--
Tim Watts
Tim Watts
> This isn't a solution though as the act of doing the test will make the
> faults more likely to occur.
Bollocks. Have you ever done any testing and inspection work?
Inspections will disturb the accessory, so you do that first[1].
The testing requires disturbing the connections at the CU only and the
first test you do is an end-end test on all 3conductors which will pick
up this problem. In fact that is the one test you could validly do with
any old cheap multimeter or even a bulb and battery.
The next test is the 500V inter-conductor insulation test.
Once those have passed, you now know that the ring is continuous and has
no single wiring error (though it may have multiple erros that cancel.
The 3rd set of figure-8 tests prove the absence of any wiring error or
open circuit fault and demonstrate the soundness of the circuit both
under load and fault conditions for all bar the most obscure and
unlikely problem scenarios.
As long as you can reinsert the wires into the CU correctly you are
good. I add an extra test of my own which is to do a few live loop
impedance tests afterwards which would pick up any issues there.
[1] As we are talking about socket circuits. Lighting circuits are more
of a PITA as you need to bridge out any electronic devices which
unfortunately means fiddling with the accessories after the tests are done.
--
Tim Watts
ARWadsworth
> "Tim Watts" <t...@dionic.net> wrote in message
> news:iecln6$rf5$1...@news.eternal-september.org...
>
>> Rings have notable safety benefits over radials, namely that the CPC
>> is doubled up over two paths.
>
> They also have several safety problems.
> They can have latent faults that the householder will only find out
> about when its too late.
> Things like broken earths (which negates your above argument) can
> just be there undetected for years unless you have regular
> inspections and real continuity tests.
> This isn't a solution though as the act of doing the test will make
> the faults more likely to occur.
>
>>
>> Also, show me a practical 32A radial with multiple socket drops
>> noting the BS standard restrictions on terminal capacities of socket
>> and FCU accessories.
>
> Why do you need a 32A radial?
> I don't think you will find them in the OSG.
Pages 49 and 158 to name two references to 32A radials in the OSG.
--
Adam
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:YscOo.49417$N41....@newsfe23.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>> news:secOo.61839$QU2....@newsfe14.ams2...
>>>
>>>> You are missing one important point.
>>>>
>>>> Ring mains are designed for normal domestic use not for clearing
>>>> floods.
>>>
>>> Shame that very few know that it can be dangerous, something that
>>> could be designed out.
>>
>>
>> The IET must be stupid. Why did they not let you design the new regs
>> for them?
>
> So you don't think they got the compromise between cost and safety on
> ring mains wrong then?
No, I believe that the compromise is very good and we have a good safe
system.
> That would be why they added radials with breakers that actually
> match the cables because they didn't need to.
I am not sure what you mean.
All circuits have breakers designed to match the cable.
> Who knows, sometime in the future when all the old electricians have
> retired rings will finally die.
Maybe, it is suggested everytime there is an update to the regs.
--
Adam
David Robinson
Yes, the rest of the circuit is 6mm T+E, from CU to cooker switch (inc
socket) to cooker outlet. It's only the last jump from cooker outlet
to adjacent single socket that's 2.5mm.
> > However, the cooker circuit may yet drop back to 32A (because I
> > suspect that's all it needs) which makes it no worse than the socket
> > spur discussed above.
>
> Indeed. In fact due to the nature of the load presented by cookers, even
> a very powerful cooker with a theoretical peak load over 60A will
> usually be fine on a 32A circuit. (cooker diversity is calculated as 10A
> plus 30% of the remainder). So a 60A cooker would need a circuit
> provisioned for 10A + 0.3 x 50 = 25A, or 30A if there is also a socket
> on the cooker point.
IIRC the cooker claims to be 13A but instructs use of heat resistant
2.5mm cable into a cooker outlet, not a 13A plug. So I've followed
those instructions.
Cheers,
David.
David Robinson
wrote:
> dennis@home <den...@killspam.kicks-ass.net> wrote:
> > "ARWadsworth" <adamwadswo...@blueyonder.co.uk> wrote in message
> >news:G5aOo.31783$ol5....@newsfe06.ams2...
>
> >>> Do I need to change my 40A to a 32A, or leave it as it is?
>
> >> I would change it. Far easier than doing calculations. However I
> >> would not use the 2.5 T&E for use with an electric cooker without
> >> making some very accurate calculations.
>
> > Its self protecting exactly as a spur on a 32A ring is (it only has a
> > single 13 socket).
>
> Yes it is at the moment, but it will not be if the OP installs an electric
> cooker, and he has hinted that he may do so.
No, see my reply to John: the rest of the circuit is 6mm T+E, and the
cooker will be run from a cooker outlet, not the socket.
Cheers,
David.
Tim Watts
> IIRC the cooker claims to be 13A but instructs use of heat resistant
> 2.5mm cable into a cooker outlet, not a 13A plug. So I've followed
> those instructions.
>
13A plugtops do have quite low specified limits on operating
temperature. Whilst it won't be a problem for a gas cooker that only
draws power for a light, spark and maybe a low powered warming cupboard,
it might be anticipated to be an issue for a cooker that actually draws
3kW (eg dual fuel with a lumpy electric oven).
--
Tim Watts
dennis@home
"Tim Watts" <t...@dionic.net> wrote in message
news:iecnie$rf5$2...@news.eternal-september.org...
> On 16/12/10 09:38, dennis@home wrote:
>>
>>
>> "Tim Watts" <t...@dionic.net> wrote in message
>> news:iecln6$rf5$1...@news.eternal-september.org...
>>
>>> Rings have notable safety benefits over radials, namely that the CPC
>>> is doubled up over two paths.
>>
>> They also have several safety problems.
>> They can have latent faults that the householder will only find out
>> about when its too late.
>> Things like broken earths (which negates your above argument) can just
>> be there undetected for years unless you have regular inspections and
>> real continuity tests.
>> This isn't a solution though as the act of doing the test will make the
>> faults more likely to occur.
>>
>>>
>>> Also, show me a practical 32A radial with multiple socket drops noting
>>> the BS standard restrictions on terminal capacities of socket and FCU
>>> accessories.
>>
>> Why do you need a 32A radial?
>
> Because 20A is fuck all use to me.
>
> I do not want to be thinking - are these sockets on the same 20A circuit -
> damn I cannot plug this 3kW appliance in because there are already two
> high load appliances on that circuit.
But you need to do that if you want to plug them into one end of a 2.5 mm
ring, even more so with three appliances.
It causes imbalance currents in the ring that can take them out of spec.
Its why fixed heating shouldn't go on a ring, they don't like high load
stuff at one end.
dennis@home
"Tim Watts" <t...@dionic.net> wrote in message
news:ieco7u$rf5$3...@news.eternal-september.org...
every time you disconnect the wire and reconnect it you work harden the
copper and make it more likely to fail due to passing traffic, etc. If the
consumer unit was correctly designed it would have test links so you could
do the tests without disconnecting the wires. But why do things right when
you can do them cheap?
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:dJlOo.37348$PE1....@newsfe29.ams2...
>> Who knows, sometime in the future when all the old electricians have
>> retired rings will finally die.
>
> Maybe, it is suggested everytime there is an update to the regs.
That would be because a lot of engineers don't think rings are safe.
Man at B&Q
wrote:
> David Robinson <davidrobin...@postmaster.co.uk> wrote:
> > In a bout of man flu, I lay in bed wondering: If the MCB is supposed
> > to protect the cable to the fitting, and the fuse in the plug is
> > supposed to protect the cable to the appliance, how is the single bit
> > of 2.5mm T+E run to a single socket spur adequately protected by
> > anything?
>
> > lengths), feeding a single bit of 2.5mm. 32A MCB.
>
> > Whereas if it was a standard radial circuit, you'd have just the
> > single bit of 2.5mm, and you'd only be allowed a 20A MCB on it. (IIRC
> > they even dropped the 2.5mm rating down to 18A, which is "correct" in
> > accordance with the calculations, but then increased it back to 20A
> > because that's what everyone does anyway).
>
>
> > I have 10cm of 2.5mm T+E protected by a 40A MCB on the cooker circuit
> > (feeding a socket that can only supply the gas hob ignition) and that
> > seems very wrong too - but wiring a socket in 6mm is just too painful.
> > suspect that's all it needs) which makes it no worse than the socket
> > spur discussed above.
>
>
> You have to consider the difference between overcurrent protection and fault
> protection.
Queue :::Jerry:::
MBQ
ARWadsworth
--
Adam
Tim Watts
>every time you disconnect the wire and reconnect it you work harden the
> copper and make it more likely to fail due to passing traffic, etc. If
> the consumer unit was correctly designed it would have test links so you
> could do the tests without disconnecting the wires. But why do things
> right when you can do them cheap?
Whilst I don't disagree with the sentiment, a decently laid out CU isn't
too bad - and your idea would require at least 3 terminals per current
terminal (L,N and PE) all with per terminal links and test points - so
that's 9 links and test points per device.
I wish that all dimmers came with a small shorting plug though, that
could be inserted from the back of the device - that would save some
faffing.
--
Tim Watts
ARWadsworth
But 60 years of history prove them wrong.
Are you going to clarify what you meant by
"That would be why they added radials with breakers that actually match the
cables because they didn't need to."
--
Adam
dennis@home
"David Robinson" <davidr...@postmaster.co.uk> wrote in message
news:52885229-931a-47fc...@j3g2000vbi.googlegroups.com...
It doesn't actually significantly change the level of protection if you fit
a full power cooker.
It does change the possibility of tripping the circuit as it allows more
current to be drawn.
However it is still safe (well as safe as a spur on a ring) as there is no
way to overload it that won't trip the circuit.
You will trip the plug fuse if you overload the socket whatever cooker you
have and trip the MCB if you overload the total circuit.
The same is true for if you fit a double socket but I wouldn't put a double
on a 2.5 mm spur in a kitchen, someone is bound to plug in a big tea urn and
a combo microwave and overload it for a couple of hours. That's what Murphy
told me.
There is quite a lot of difference between it being safe and it being user
friendly, you don't want circuits to trip frequently to maintain safety.
Man at B&Q
ARWadsworth
dennis@home
"Tim Watts" <t...@dionic.net> wrote in message
news:iecvi1$rf5$6...@news.eternal-september.org...
> On 16/12/10 11:53, dennis@home wrote:
>
>>every time you disconnect the wire and reconnect it you work harden the
>> copper and make it more likely to fail due to passing traffic, etc. If
>> the consumer unit was correctly designed it would have test links so you
>> could do the tests without disconnecting the wires. But why do things
>> right when you can do them cheap?
>
> Whilst I don't disagree with the sentiment, a decently laid out CU isn't
> too bad - and your idea would require at least 3 terminals per current
> terminal (L,N and PE) all with per terminal links and test points - so
> that's 9 links and test points per device.
Less if its not a ring though.
>
> I wish that all dimmers came with a small shorting plug though, that could
> be inserted from the back of the device - that would save some faffing.
You should invent one.. a crimp on termination pin for each wire with a
suitable socket should do it.
>
> --
> Tim Watts
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:7lnOo.49369$oI6....@newsfe05.ams2...
> dennis@home <den...@killspam.kicks-ass.net> wrote:
>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>> news:dJlOo.37348$PE1....@newsfe29.ams2...
>>
>>>> Who knows, sometime in the future when all the old electricians have
>>>> retired rings will finally die.
>>>
>>> Maybe, it is suggested everytime there is an update to the regs.
>>
>> That would be because a lot of engineers don't think rings are safe.
>
> But 60 years of history prove them wrong.
How does it?
Nobody knows how many faulty rings there are as the householder doesn't know
and very few are ever checked.
There could be 10 there could be 100,000, until people get hurt no one
cares.
>
> Are you going to clarify what you meant by
>
> "That would be why they added radials with breakers that actually match
> the cables because they didn't need to."
It is illogical to rely on downstream breakers to protect up stream cables.
It makes modification to the circuit potentially dangerous.
People do modify the circuits by putting the wrong fuse in plugs (including
nails) rendering them useless for protecting the upstream circuit against
overload.
There was even a large batch of "genuine" fuses for plugs that didn't
protect the circuit a few decades back.
These led to certification being required to show batch testing had been
done.
God knows how many of these faulty fuses are still out there.
Do you check the plug fuse for certification when you come across one?
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:7lnOo.49369$oI6....@newsfe05.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>> news:dJlOo.37348$PE1....@newsfe29.ams2...
>>>
>>>>> Who knows, sometime in the future when all the old electricians
>>>>> have retired rings will finally die.
>>>>
>>>> Maybe, it is suggested everytime there is an update to the regs.
>>>
>>> That would be because a lot of engineers don't think rings are safe.
>>
>> But 60 years of history prove them wrong.
>
> How does it?
> Nobody knows how many faulty rings there are as the householder
> doesn't know and very few are ever checked.
> There could be 10 there could be 100,000, until people get hurt no one
> cares.
Ditto for faulty radials.
>> Are you going to clarify what you meant by
>>
>> "That would be why they added radials with breakers that actually
>> match the cables because they didn't need to."
>
> It is illogical to rely on downstream breakers to protect up stream
> cables. It makes modification to the circuit potentially dangerous.
Only if you do not know what you are doing.
> People do modify the circuits by putting the wrong fuse in plugs
> (including nails) rendering them useless for protecting the upstream
> circuit against overload.
Non of which alters the load on the spur or makes any difference at all to a
fault current on the spur.
> There was even a large batch of "genuine" fuses for plugs that didn't
> protect the circuit a few decades back.
> These led to certification being required to show batch testing had
> been done.
> God knows how many of these faulty fuses are still out there.
> Do you check the plug fuse for certification when you come across one?
And the relevance to spurs and radials is?
--
Adam
ARWadsworth
> On 16/12/10 09:38, dennis@home wrote:
>>
>>
>> "Tim Watts" <t...@dionic.net> wrote in message
>> news:iecln6$rf5$1...@news.eternal-september.org...
>>
>>> Rings have notable safety benefits over radials, namely that the CPC
>>> is doubled up over two paths.
>>
>> They also have several safety problems.
>> They can have latent faults that the householder will only find out
>> about when its too late.
>> Things like broken earths (which negates your above argument) can
>> just be there undetected for years unless you have regular
>> inspections and real continuity tests.
>> This isn't a solution though as the act of doing the test will make
>> the faults more likely to occur.
>>
>>>
>>> Also, show me a practical 32A radial with multiple socket drops
>>> noting the BS standard restrictions on terminal capacities of
>>> socket and FCU accessories.
>>
>> Why do you need a 32A radial?
>
> Because 20A is fuck all use to me.
20A radials often use more cable when installing than a ring, offer very
little in the way of diversity and require just as much (if not more) work
to install than a ring.
There are times when they are useful but not very often.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:3apOo.54821$ro5....@newsfe24.ams2...
> dennis@home <den...@killspam.kicks-ass.net> wrote:
>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>> news:7lnOo.49369$oI6....@newsfe05.ams2...
>>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>>> news:dJlOo.37348$PE1....@newsfe29.ams2...
>>>>
>>>>>> Who knows, sometime in the future when all the old electricians
>>>>>> have retired rings will finally die.
>>>>>
>>>>> Maybe, it is suggested everytime there is an update to the regs.
>>>>
>>>> That would be because a lot of engineers don't think rings are safe.
>>>
>>> But 60 years of history prove them wrong.
>>
>> How does it?
>> Nobody knows how many faulty rings there are as the householder
>> doesn't know and very few are ever checked.
>> There could be 10 there could be 100,000, until people get hurt no one
>> cares.
>
> Ditto for faulty radials.
Faulty radials are likely to be noticed by the householder, things like
sockets that don't work.
Most of the other faults can be found with a simple plug in tester from
Argos.
>
>>> Are you going to clarify what you meant by
>>>
>>> "That would be why they added radials with breakers that actually
>>> match the cables because they didn't need to."
>>
>> It is illogical to rely on downstream breakers to protect up stream
>> cables. It makes modification to the circuit potentially dangerous.
>
> Only if you do not know what you are doing.
>
>> People do modify the circuits by putting the wrong fuse in plugs
>> (including nails) rendering them useless for protecting the upstream
>> circuit against overload.
>
> Non of which alters the load on the spur or makes any difference at all to
> a fault current on the spur.
Of course it can alter the load.
There is nothing to stop it.
>
>> There was even a large batch of "genuine" fuses for plugs that didn't
>> protect the circuit a few decades back.
>> These led to certification being required to show batch testing had
>> been done.
>> God knows how many of these faulty fuses are still out there.
>> Do you check the plug fuse for certification when you come across one?
>
> And the relevance to spurs and radials is?
See above, its obvious once you realise that it can alter the load.
Without a working fuse in the plug there is nothing to stop you overloading
a spur.
There is even an argument that it could overload the ring itself if the plug
is in the "wrong" socket.
Man at B&Q
wrote:
> >> People do modify the circuits by putting the wrong fuse in plugs
> >> (including nails) rendering them useless for protecting the upstream
> >> circuit against overload.
>
> > Non of which alters the load on the spur or makes any difference at all to
> > a fault current on the spur.
>
> Of course it can alter the load.
> There is nothing to stop it.
You really are as thick as Jerry. I thought this was done to death a
few weeks ago.
Putting the wrong fuse or a nail in a plug top does NOT alter the
load. The load will draw whatever current it draws, regardless of
whether it does so through a fuse (correct or incorrect) or a nail. I
am, of course, assuming that the nail and all fuses in question are
rated for the normal load current.
Now, if you want to talk about what happens in the event of a fault...
MBQ
John Rumm
If its just using it for ignition, and displays. lights etc, then it
will be a tiny load. Even a single electric oven will tend to be under
2.5kW.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
John Rumm
> On 16/12/10 11:53, dennis@home wrote:
>
>> every time you disconnect the wire and reconnect it you work harden the
>> copper and make it more likely to fail due to passing traffic, etc. If
>> the consumer unit was correctly designed it would have test links so you
>> could do the tests without disconnecting the wires. But why do things
>> right when you can do them cheap?
>
> Whilst I don't disagree with the sentiment, a decently laid out CU isn't
> too bad - and your idea would require at least 3 terminals per current
> terminal (L,N and PE) all with per terminal links and test points - so
> that's 9 links and test points per device.
And since screwed connections tend to be a failure point in circuits,
why introduce more of them!
> I wish that all dimmers came with a small shorting plug though, that
> could be inserted from the back of the device - that would save some
> faffing.
or just design them all so they are "safe" to IR test.
John Rumm
> dennis@home<den...@killspam.kicks-ass.net> wrote:
>> "ARWadsworth"<adamwa...@blueyonder.co.uk> wrote in message
>> news:dJlOo.37348$PE1....@newsfe29.ams2...
>>
>>>> Who knows, sometime in the future when all the old electricians have
>>>> retired rings will finally die.
>>>
>>> Maybe, it is suggested everytime there is an update to the regs.
>>
>> That would be because a lot of engineers don't think rings are safe.
>
> But 60 years of history prove them wrong.
More to the point, modern patterns of usage[1], are also very well
suited to ring circuits - so in a sense they are more rather than less
appropriate now than at any time in the past.
[1] a large number of small loads scattered over a wide area, and a few
larger loads that tend to be used intermittently in different places
around the house. The exception to that is a kitchen, but even there
assuming the layout is not unduly unbalanced, its a good way to supply a
shed load of power without making the physical aspects of wiring
particularly difficult.
Tim Watts
> On 16/12/2010 12:09, Tim Watts wrote:
>> On 16/12/10 11:53, dennis@home wrote:
>>
>>> every time you disconnect the wire and reconnect it you work harden the
>>> copper and make it more likely to fail due to passing traffic, etc. If
>>> the consumer unit was correctly designed it would have test links so you
>>> could do the tests without disconnecting the wires. But why do things
>>> right when you can do them cheap?
>>
>> Whilst I don't disagree with
the sentiment, a decently laid out CU isn't
>> too bad - and your idea would require at least 3 terminals per current
>> terminal (L,N and PE) all with per terminal links and test points - so
>> that's 9 links and test points per device.
>
> And since screwed connections tend to be a failure point in circuits,
> why introduce more of them!
>
>> I wish that all dimmers came with a small shorting plug though, that
>> could be inserted from the back of the device - that would save some
>> faffing.
>
> or just design them all so they are "safe" to IR test.
>
You could do what Adam suggests and test LN->PE at 500V, then, just to
be pedantic, test L,L,PE in all combos at 250V.
But I suspect any decent electronics will be happy at 500V DC seeing as
that isn't much more than the top of the 240V sine plus a few spikes.
Part of the idea with the shorting link though, was to aid the R1+R2
(and R1+Rn) tests - means disturbing no terminals other than the CU.
--
Tim Watts
Tim Watts
> On 16/12/2010 12:10, ARWadsworth wrote:
>> dennis@home<den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth"<adamwa...@blueyonder.co.uk> wrote in message
>>> news:dJlOo.37348$PE1....@newsfe29.ams2...
>>>
>>>>> Who knows, sometime in the future when all the old electricians have
>>>>> retired rings will finally die.
>>>>
>>>> Maybe, it is suggested everytime there is an update to the regs.
>>>
>>> That would be because a lot of engineers don't think rings are safe.
>>
>> But 60 years of history prove them wrong.
>
> More to the point, modern patterns of usage[1], are also very well
> suited to ring circuits - so in a sense they are more rather than less
> appropriate now than at any time in the past.
>
> [1] a large number of small loads scattered over a wide area, and a few
> larger loads that tend to be used intermittently in different places
> around the house. The exception to that is a kitchen, but even there
> assuming the layout is not unduly unbalanced, its a good way to supply a
> shed load of power without making the physical aspects of wiring
> particularly difficult.
>
Exactly my thinking.
I have one short ring[1] in the kitchen for 2 doubles and 3 fixed
appliances, another lower loaded but loads-of-sockets kitchen ring that
is shared with the adjacent bedroom, 3rd ring doing the other 2 bedrooms
and hall and potentially a 4th upstairs (in the dormer).
[1] This ring got special attention - one end finished right next to the
CU, the other end is 3m away. I actually ran both legs along the joists
to the opposing external wall (ring is on the centre wall), along a bit
then straight back to the CU - "wasting" about 8m cable per leg but
ensuring they remain balanced.
Testing with a clamp meter, each leg is balanced to about 45% vs 55%
which is pretty good - I had it loaded up with *all* my oil heaters -
total load 42A for 10 minutes. Cables just pereceptibly warm where they
went as a pair down a short bit of 20mm conduit into the top of the CU.
Dread to think how it would have behaved if I hadn't balanced it.
Others might have called for 2x20A radials there, but the rational was
the same - one radial might have had 20-ish A from a double socket plus
a tumble dryer for probably long enough to trip a 20A breaker, while the
other might have had a dishwasher and bugger all else. Depends on how
you layout the appliances, kettle and microwave...
--
Tim Watts
ARWadsworth
That is actually pretty neat.
> Dread to think how it would have behaved if I hadn't balanced it.
A 33 to 67 balance/split is usually aceptable.
> Others might have called for 2x20A radials there, but the rational was
> the same - one radial might have had 20-ish A from a double socket
> plus a tumble dryer for probably long enough to trip a 20A breaker,
> while the other might have had a dishwasher and bugger all else.
> Depends on how you layout the appliances, kettle and microwave...
And the daft thing is, I believe that a 4mm 32A radial is often ideal to
remove the high loads such as a washer and tumble dryer. I do not have
anything against radials when used correctly. Removing the loads from a
washer and drier makes the rest of the load on the kitchen ring irrelevant.
A kettle is used for a few minutes at a time and so is the microwave etc.
And there is no point in designing a circuit to suit the appliance layout if
you are married.
--
Adam
dennis@home
"Man at B&Q" <manat...@hotmail.com> wrote in message
news:7dbe3c68-1c09-419b...@m20g2000prc.googlegroups.com...
You are the one being thick!
What if the nail is in a fourway strip?
Now go away and think about it.
> Now, if you want to talk about what happens in the event of a fault...
With someone that doesn't even know multiway strips exist?
Why bother?
dennis@home
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:WIWdnaS-Bp0z3pfQ...@brightview.co.uk...
> On 16/12/2010 12:09, Tim Watts wrote:
>> On 16/12/10 11:53, dennis@home wrote:
>>
>>> every time you disconnect the wire and reconnect it you work harden the
>>> copper and make it more likely to fail due to passing traffic, etc. If
>>> the consumer unit was correctly designed it would have test links so you
>>> could do the tests without disconnecting the wires. But why do things
>>> right when you can do them cheap?
>>
>> Whilst I don't disagree with the sentiment, a decently laid out CU isn't
>> too bad - and your idea would require at least 3 terminals per current
>> terminal (L,N and PE) all with per terminal links and test points - so
>> that's 9 links and test points per device.
>
> And since screwed connections tend to be a failure point in circuits, why
> introduce more of them!
Who said to use screws?
ARWadsworth
The multiway strip will melt. Just as it usually does even when protected by
a 13A fuse.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:1wtOo.31428$WJ4....@newsfe12.ams2...
> The multiway strip will melt. Just as it usually does even when protected
> by a 13A fuse.
That's probably the best outcome, however Murphy says the cable will melt,
the PVC will emit lots of smoke killing the kids, the copper will spark and
the building will burn down cremating the dead. After all they won't have a
smoke alarm.
ARWadsworth
And it will have nothing to do with a correctly installed ring (including
spurs) or radial circuit.
And your point about spurs from a ring was?
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:vQtOo.40221$M94....@newsfe22.ams2...
A radial circuit will not do that, the breaker will trip before the cable
can melt as no cable is rated below the breakers rating.
A spur on a ring will be overloaded as the only thing preventing the
overload on the spur is the nail in the plug (and we all know how good they
are don't we?). The 2.5 mm cable is below the rating of the breaker so it
can be overloaded unless the plug fuse works.
I thought that was the obvious bit.
>
> And your point about spurs from a ring was?
see the obvious bit above.
ARWadsworth
>>>> The multiway strip will melt. Just as it usually does even when
>>>> protected by a 13A fuse.
>>>
>>> That's probably the best outcome, however Murphy says the cable will
>>> melt, the PVC will emit lots of smoke killing the kids, the copper
>>> will spark and the building will burn down cremating the dead. After
>>> all they won't have a smoke alarm.
>>
>> And it will have nothing to do with a correctly installed ring
>> (including spurs) or radial circuit.
>
> A radial circuit will not do that, the breaker will trip before the
> cable can melt as no cable is rated below the breakers rating.
Would you bet your life on that? I will happily bet my life that you are
wrong. You have never read BS 7671:2008 and you have never read the part on
32A radials.
--
Adam
Man at B&Q
wrote:
> "Man at B&Q" <manatba...@hotmail.com> wrote in messagenews:7dbe3c68-1c09-419b...@m20g2000prc.googlegroups.com...
>
>
>
> > On Dec 16, 2:31 pm, "dennis@home" <den...@killspam.kicks-ass.net>
> > wrote:
>
> >> >> People do modify the circuits by putting the wrong fuse in plugs
> >> >> (including nails) rendering them useless for protecting the upstream
> >> >> circuit against overload.
>
> >> > Non of which alters the load on the spur or makes any difference at all
> >> > to
> >> > a fault current on the spur.
>
> >> Of course it can alter the load.
> >> There is nothing to stop it.
>
> > You really are as thick as Jerry. I thought this was done to death a
> > few weeks ago.
>
> > Putting the wrong fuse or a nail in a plug top does NOT alter the
> > load. The load will draw whatever current it draws, regardless of
> > whether it does so through a fuse (correct or incorrect) or a nail. I
> > am, of course, assuming that the nail and all fuses in question are
> > rated for the normal load current.
>
> You are the one being thick!
> What if the nail is in a fourway strip?
Then you deserve all you get. You really ought to know better.
MBQ
Man at B&Q
wrote:
> "ARWadsworth" <adamwadswo...@blueyonder.co.uk> wrote in message
>
> news:1wtOo.31428$WJ4....@newsfe12.ams2...
>
> > The multiway strip will melt. Just as it usually does even when protected
> > by a 13A fuse.
>
> That's probably the best outcome, however Murphy says the cable will melt,
> the PVC will emit lots of smoke killing the kids,
The whole dennis line wiped out for want of a fuse...
ARWadsworth
Fingers crossed.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:VeuOo.40225$M94....@newsfe22.ams2...
So what have they done wrong in designing 32A radials then?
dennis@home
"Man at B&Q" <manat...@hotmail.com> wrote in message
news:646cacda-061d-47a7...@t35g2000yqj.googlegroups.com...
> Then you deserve all you get. You really ought to know better.
And what about the poor suckers that have fuses from that batches that
didn't blow at the correct current, I suppose they deserve it to for being
stupid enough to trust electricians with their lives?
ARWadsworth
Did an elecrician buy or install the fuse?
--
Adam
ARWadsworth
You tell me. You claim to know it all.
Lets just say that a 32A radial uses 4mm cable apart from the 2.5mm unfused
spurs.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:2DuOo.64450$QU2....@newsfe14.ams2...
Your the one claiming 32A radials are dangerous.
>
> Lets just say that a 32A radial uses 4mm cable apart from the 2.5mm
> unfused spurs.
Are you saying there are people stupid enough to spur off in 2.5 mm even
when they know its wrong on ring mains? Why don't they go the whole hog and
use 1.5 mm as that can supply a single spur without additional problems?
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:hBuOo.42271$Dq6....@newsfe19.ams2...
Probably.
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:2DuOo.64450$QU2....@newsfe14.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>> news:VeuOo.40225$M94....@newsfe22.ams2...
>>>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>>>
>>>>
>>>>>>>> The multiway strip will melt. Just as it usually does even when
>>>>>>>> protected by a 13A fuse.
>>>>>>>
>>>>>>> That's probably the best outcome, however Murphy says the cable
>>>>>>> will melt, the PVC will emit lots of smoke killing the kids, the
>>>>>>> copper will spark and the building will burn down cremating the
>>>>>>> dead. After all they won't have a smoke alarm.
>>>>>>
>>>>>> And it will have nothing to do with a correctly installed ring
>>>>>> (including spurs) or radial circuit.
>>>>>
>>>>> A radial circuit will not do that, the breaker will trip before
>>>>> the cable can melt as no cable is rated below the breakers rating.
>>>>
>>>> Would you bet your life on that? I will happily bet my life that
>>>> you are wrong. You have never read BS 7671:2008 and you have never
>>>> read the part on 32A radials.
>>>
>>> So what have they done wrong in designing 32A radials then?
>>
>> You tell me. You claim to know it all.
>
> Your the one claiming 32A radials are dangerous.
I am claiming so such thing. I am claiming that you do not know about
radials.
>> Lets just say that a 32A radial uses 4mm cable apart from the 2.5mm
>> unfused spurs.
>
> Are you saying there are people stupid enough to spur off in 2.5 mm
> even when they know its wrong on ring mains? Why don't they go the
> whole hog and use 1.5 mm as that can supply a single spur without
> additional problems?
There are people who spur off a 4mm 32A radial in 2.5mm. But you didn't know
that was allowed by the regs. Your lack of knowledge of the regs is showing
again.
--
Adam
ARWadsworth
Probably not. Most people do not call an electrician out to swap a fuse in a
plug.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:NgHOo.52152$N41....@newsfe23.ams2...
> There are people who spur off a 4mm 32A radial in 2.5mm. But you didn't
> know that was allowed by the regs. Your lack of knowledge of the regs is
> showing again.
I don't need to know the regs allow that, I wouldn't do it as I consider it
no better than a ring and I don't like those either.
I prefer safety to cost savings.
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:NgHOo.52152$N41....@newsfe23.ams2...
>
>
>> There are people who spur off a 4mm 32A radial in 2.5mm. But you
>> didn't know that was allowed by the regs. Your lack of knowledge of
>> the regs is showing again.
>
> I don't need to know the regs allow that,
So stop incorrectly quoting the regs then.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:78QOo.47850$sA4....@newsfe28.ams2...
I didn't quote the regs.
ARWadsworth
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:78QOo.47850$sA4....@newsfe28.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>>> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
>>> news:NgHOo.52152$N41....@newsfe23.ams2...
>>>
>>>
>>>> There are people who spur off a 4mm 32A radial in 2.5mm. But you
>>>> didn't know that was allowed by the regs. Your lack of knowledge of
>>>> the regs is showing again.
>>>
>>> I don't need to know the regs allow that,
>>
>> So stop incorrectly quoting the regs then.
>
> I didn't quote the regs.
Obviously, as you have never read them.
You just made comment on a radial that was incorrect.
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:08ROo.7171$_k1....@newsfe17.ams2...
The comment I said was that people with sense don't put 2.5mm T&E cable into
32A circuits and that applies to rings and spurs and anything else. You may
regard it as wrong in which case I will still say its wrong. I am not alone,
there are many members of the IEE that also hold this view. I don't really
care what the regs say as I regard them as wrong and encouraging dangerous
practices just to save a miniscule amount of cash. What I propose does not
breech the regs and is an improvement on them which is something you cannot
deny.
ARWadsworth
>>>> So stop incorrectly quoting the regs then.
>>>
>>> I didn't quote the regs.
>>
>> Obviously, as you have never read them.
>>
>> You just made comment on a radial that was incorrect.
>
> The comment I said was that people with sense don't put 2.5mm T&E
> cable into 32A circuits and that applies to rings and spurs and
> anything else. You may regard it as wrong in which case I will still
> say its wrong. I am not alone, there are many members of the IEE that
> also hold this view. I don't really care what the regs say as I
> regard them as wrong and encouraging dangerous practices just to save
> a miniscule amount of cash. What I propose does not breech the regs
> and is an improvement on them which is something you cannot deny.
That is not what you said. It is just lie after lie with you. That plus
careful snipping of posts so that your lies do not show up. What you said
was "That would be why they added radials with breakers that actually match
the cables because they didn't need to".
Is it easier for you to lie than just admit that you made a comment about
radials that was incorrect?
--
Adam
dennis@home
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:4v%Oo.46640$Dq6....@newsfe19.ams2...
And where is that false?
They did exactly that but not with 32A breakers.
>
> Is it easier for you to lie than just admit that you made a comment about
> radials that was incorrect?
>
Well state which one was incorrect the one you quoted was correct.
So far you have been posting stuff calling me a liar while quoting stuff
that isn't a lie.
BruceB
"dennis@home" wrote in message news:iegn8c$j0f$1...@news.datemas.de...
The comment I said was that people with sense don't put 2.5mm T&E cable into
32A circuits and that applies to rings and spurs and anything else. You may
regard it as wrong in which case I will still say its wrong. I am not alone,
there are many members of the IEE that also hold this view. I don't really
care what the regs say as I regard them as wrong and encouraging dangerous
practices just to save a miniscule amount of cash. What I propose does not
breech the regs and is an improvement on them which is something you cannot
deny.
******************************************
I think that is rubbish saying people with sense don't put 2.5mm2 cable into
32A circuits. It suggests that you do not understand the reasoning behind
the regs, which from a quick scan of the other posts looks well explained.
If overload protection is covered by another means then a 32A mcb will in
most circumstances provide adequate fault protection to 2.5mm2 cable. In
fact there are situations where the use of 4mm2 cable INCREASES the risk
under fault conditions. The reason is that the cpc conductor in 4mm2 cable
is only 1.5mm2, so under fault conditions the touch voltage will be higher
than with 2.5mm2 cable.
Regards
Bruce
dennis@home
"BruceB" <n...@nul.com> wrote in message
news:ieib20$bfp$1...@news.eternal-september.org...
>
>
> "dennis@home" wrote in message news:iegn8c$j0f$1...@news.datemas.de...
>
> The comment I said was that people with sense don't put 2.5mm T&E cable
> into
> 32A circuits and that applies to rings and spurs and anything else. You
> may
> regard it as wrong in which case I will still say its wrong. I am not
> alone,
> there are many members of the IEE that also hold this view. I don't really
> care what the regs say as I regard them as wrong and encouraging dangerous
> practices just to save a miniscule amount of cash. What I propose does not
> breech the regs and is an improvement on them which is something you
> cannot
> deny.
>
> ******************************************
>
> I think that is rubbish saying people with sense don't put 2.5mm2 cable
> into 32A circuits. It suggests that you do not understand the reasoning
> behind the regs,
Oh I understand the idea, I just don't agree with it.
> which from a quick scan of the other posts looks well explained.
Yes its well explained why they think its OK, it doesn't mean everyone
agrees with it.
It relies on the fuse in the plug to give overload protection to the spur.
While this is fine in principle it isn't a good idea.
The plug fuse is a user serviceable part and is going to be abused, we know
it is abused.
It also not tested. Virtually no PAT testing is done and even then they
seldom actually check the fuse is OK.
Electricians doing PIRs don't even care about the plug fuse despite it being
*essential* to protect the circuit they have just tested and approved. The
majority of householders don't even know its essential.
It is far more sensible to rate the breaker so that the cable is protected
whatever the householder does rather than saying well he would still be
alive if he hadn't done something to the fuse in the plug.
Its like supplying a power press where the user has to fit parts to make it
safe.
> If overload protection is covered by another means then a 32A mcb will in
> most circumstances provide adequate fault protection to 2.5mm2 cable. In
> fact there are situations where the use of 4mm2 cable INCREASES the risk
> under fault conditions. The reason is that the cpc conductor in 4mm2
> cable is only 1.5mm2, so under fault conditions the touch voltage will be
> higher than with 2.5mm2 cable.
That sounds more like a case to make the CPC bigger not to rely on the
consumer provided plug fuse to protect the circuit.
BTW AFAIK 32A radials are not the preferred radial, certainly not by me.
dennis@home
"BruceB" <n...@nul.com> wrote in message
news:ieib20$bfp$1...@news.eternal-september.org...
>
>
> "dennis@home" wrote in message news:iegn8c$j0f$1...@news.datemas.de...
>
> The comment I said was that people with sense don't put 2.5mm T&E cable
> into
> 32A circuits and that applies to rings and spurs and anything else. You
> may
> regard it as wrong in which case I will still say its wrong. I am not
> alone,
> there are many members of the IEE that also hold this view. I don't really
> care what the regs say as I regard them as wrong and encouraging dangerous
> practices just to save a miniscule amount of cash. What I propose does not
> breech the regs and is an improvement on them which is something you
> cannot
> deny.
>
> ******************************************
>
> I think that is rubbish saying people with sense don't put 2.5mm2 cable
> into 32A circuits. It suggests that you do not understand the reasoning
> behind the regs,
Oh I understand the idea, I just don't agree with it.
> which from a quick scan of the other posts looks well explained.
Yes its well explained why they think its OK, it doesn't mean everyone
agrees with it.
It relies on the fuse in the plug to give overload protection to the spur.
While this is fine in principle it isn't a good idea.
The plug fuse is a user serviceable part and is going to be abused, we know
it is abused.
It also not tested. Virtually no PAT testing is done and even then they
seldom actually check the fuse is OK.
Electricians doing PIRs don't even care about the plug fuse despite it being
*essential* to protect the circuit they have just tested and approved. The
majority of householders don't even know its essential.
It is far more sensible to rate the breaker so that the cable is protected
whatever the householder does rather than saying well he would still be
alive if he hadn't done something to the fuse in the plug.
Its like supplying a power press where the user has to fit parts to make it
safe.
> If overload protection is covered by another means then a 32A mcb will in
> most circumstances provide adequate fault protection to 2.5mm2 cable. In
> fact there are situations where the use of 4mm2 cable INCREASES the risk
> under fault conditions. The reason is that the cpc conductor in 4mm2
> cable is only 1.5mm2, so under fault conditions the touch voltage will be
> higher than with 2.5mm2 cable.
That sounds more like a case to make the CPC bigger not to rely on the
Adam Wadsworth
wrote:
> "ARWadsworth" <adamwadswo...@blueyonder.co.uk> wrote in message
>
> news:4v%Oo.46640$Dq6....@newsfe19.ams2...
>
>
>
>
>
> > dennis@home <den...@killspam.kicks-ass.net> wrote:
> >>>>> So stop incorrectly quoting the regs then.
>
> >>>> I didn't quote the regs.
>
> >>> Obviously, as you have never read them.
>
> >>> You just made comment on a radial that was incorrect.
>
> >> The comment I said was that people with sense don't put 2.5mm T&E
> >> cable into 32A circuits and that applies to rings and spurs and
> >> anything else. You may regard it as wrong in which case I will still
> >> say its wrong. I am not alone, there are many members of the IEE that
> >> also hold this view. I don't really care what the regs say as I
> >> regard them as wrong and encouraging dangerous practices just to save
> >> a miniscule amount of cash. What I propose does not breech the regs
> >> and is an improvement on them which is something you cannot deny.
>
> > That is not what you said. It is just lie after lie with you. That plus
> > careful snipping of posts so that your lies do not show up. What you said
> > was "That would be why they added radials with breakers that actually
> > match the cables because they didn't need to".
>
> And where is that false?
> They did exactly that but not with 32A breakers.
So it is an incorrect comment about 32A radials that you made then.
You just said radials and made no mention of MCB sizes. You are only
mentioning 32A radials now as you now have an idea how they can be
wired up, something that you did not know before I corrected you.
> > Is it easier for you to lie than just admit that you made a comment about
> > radials that was incorrect?
>
> Well state which one was incorrect the one you quoted was correct.
Well your quote is in this post.
> So far you have been posting stuff calling me a liar while quoting stuff
> that isn't a lie.
Maybe your are stupid and not a liar then.
- Hide quoted text -
>
> - Show quoted text -
--
Adam
Adam Wadsworth
wrote:
> "Man at B&Q" <manatba...@hotmail.com> wrote in messagenews:646cacda-061d-47a7...@t35g2000yqj.googlegroups.com...
>
> > Then you deserve all you get. You really ought to know better.
>
> And what about the poor suckers that have fuses from that batches that
> didn't blow at the correct current, I suppose they deserve it to for being
> stupid enough to trust electricians with their lives?
So how do you test these made up in your imagination fuses then?
--
Adam
dennis@home
"Adam Wadsworth" <adamawayfromh...@gmail.com> wrote in message
news:8f89cd40-2604-4c9d...@u3g2000vbj.googlegroups.com...
And that quote is correct, no matter what you add to try and make it false
it is still true.
Try analysing it and then think about what radials they added last, a hint
it wasn't 32A radials it was radials designed about 2.5 mm cable with a
breaker that made it safe. Therefore what I stated is true.
>
>> So far you have been posting stuff calling me a liar while quoting stuff
>> that isn't a lie.
>
> Maybe your are stupid and not a liar then.
>
Maybe you are deliberately trying to distort what I said?
dennis@home
"Adam Wadsworth" <adamawayfromh...@gmail.com> wrote in message
news:3a2efc2e-065a-48ad...@i41g2000vbn.googlegroups.com...
Well that would be the problem.
John Rumm
>
>
> "ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
> news:4v%Oo.46640$Dq6....@newsfe19.ams2...
>> dennis@home <den...@killspam.kicks-ass.net> wrote:
>> That is not what you said. It is just lie after lie with you. That
>> plus careful snipping of posts so that your lies do not show up. What
>> you said was "That would be why they added radials with breakers that
>> actually match the cables because they didn't need to".
>
> And where is that false?
> They did exactly that but not with 32A breakers.
Sounds like a load twaddle to me. Care to cite the edition of BS7671?
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
John Rumm
>
>
> "BruceB" <n...@nul.com> wrote in message
> news:ieib20$bfp$1...@news.eternal-september.org...
>>
>>
>> "dennis@home" wrote in message news:iegn8c$j0f$1...@news.datemas.de...
>>
>> The comment I said was that people with sense don't put 2.5mm T&E
>> cable into
>> 32A circuits and that applies to rings and spurs and anything else.
>> You may
>> regard it as wrong in which case I will still say its wrong. I am not
>> alone,
>> there are many members of the IEE that also hold this view. I don't
>> really
>> care what the regs say as I regard them as wrong and encouraging
>> dangerous
>> practices just to save a miniscule amount of cash. What I propose does
>> not
>> breech the regs and is an improvement on them which is something you
>> cannot
>> deny.
>>
>> ******************************************
>>
>> I think that is rubbish saying people with sense don't put 2.5mm2
>> cable into 32A circuits. It suggests that you do not understand the
>> reasoning behind the regs,
>
> Oh I understand the idea, I just don't agree with it.
But dennis you disagree with most things as a matter of principle - that
alone add little weight to an argument.
>> which from a quick scan of the other posts looks well explained.
>
> Yes its well explained why they think its OK, it doesn't mean everyone
> agrees with it.
>
> It relies on the fuse in the plug to give overload protection to the spur.
> While this is fine in principle it isn't a good idea.
That's not true, since there is no requirement for any fuse in the spur
- the spur could quite legitimately have an unfused flex outlet on the
end of it, and everything would remain well protected. The overload
protection of the spur being enforced by controlling the size of the
load - not by fusing, and the fault protection being maintained at the
origin of the circuit by the 32A MCB.
> The plug fuse is a user serviceable part and is going to be abused, we
> know it is abused.
Is it equally easy to uprate your vacuum cleaner to 5kW for this non
sequiter to have any relevance?
Yes your could probably bodge a 4 way trailing lead and stick two 3kW
fan heaters on it, but as has been observed in testing the lead will
fail long before the fixed wiring is at risk.
> It also not tested. Virtually no PAT testing is done and even then they
> seldom actually check the fuse is OK.
> Electricians doing PIRs don't even care about the plug fuse despite it
> being *essential* to protect the circuit they have just tested and
> approved. The majority of householders don't even know its essential.
You seem to think that plug fuses are designed to protect against
overload, this is not the case. They are there for the fault protection
of the flex connected to them. The common exception to this is with
multiway extension leads, but this is not of relevance to the fixed wiring.
If we extend your argument to its logical conclusion, every table lamp
ought to have a 4mm^2 flex so that it matches the trip threshold of the
circuit breaker.
> It is far more sensible to rate the breaker so that the cable is
> protected whatever the householder does rather than saying well he would
Which is exactly what the current circuit designs that permit 2.5mm^2
cable on 32A breakers do. The breaker provides fault protection at all
times. Overload protection some of the time.
> still be alive if he hadn't done something to the fuse in the plug.
> Its like supplying a power press where the user has to fit parts to make
> it safe.
>
>
>> If overload protection is covered by another means then a 32A mcb will
>> in most circumstances provide adequate fault protection to 2.5mm2
>> cable. In fact there are situations where the use of 4mm2 cable
>> INCREASES the risk under fault conditions. The reason is that the cpc
>> conductor in 4mm2 cable is only 1.5mm2, so under fault conditions the
>> touch voltage will be higher than with 2.5mm2 cable.
>
> That sounds more like a case to make the CPC bigger not to rely on the
> consumer provided plug fuse to protect the circuit.
It highlights why rings tend to perform better than radials with regard
to earth faults. It also helps explain why when high integrity earthing
is use on a radial circuit, it is done by turning the protective
conductor into a *ring*
> BTW AFAIK 32A radials are not the preferred radial, certainly not by me.
A 32A radial in 4mm^2 T&E is a standard circuit. Just as is a 20A one in
2.5mm^2 cable. The 32A version is however far more useful as a general
purpose socket circuit.
John Rumm
The same way he tests a match to make sure its not a dud... ;-)
John Rumm
Its pretty straight forward if you know anything about manufacturing
processes. You pull out a sample of production on a regular basis and
subject that to destructive testing against an agreed BS test procedure.
If they fail to meet spec, you bin or rework that batch of production
output.
Adam Wadsworth
> On 18/12/2010 14:59, Adam Wadsworth wrote:
>
> > On Dec 16, 8:18 pm, "dennis@home"<den...@killspam.kicks-ass.net>
> > wrote:
> >> "Man at B&Q"<manatba...@hotmail.com> wrote in messagenews:646cacda-061d-47a7...@t35g2000yqj.googlegroups.com...
>
> >>> Then you deserve all you get. You really ought to know better.
>
> >> And what about the poor suckers that have fuses from that batches that
> >> didn't blow at the correct current, I suppose they deserve it to for being
> >> stupid enough to trust electricians with their lives?
>
> > So how do you test these made up in your imagination fuses then?
>
> The same way he tests a match to make sure its not a dud... ;-)
vbg
To be fair you are pretty screwed if the fuses are illegal copies from
China with all the correct BS numbers stamped on them. However the 2.5
T&E unfused spur is not the bit that will suffer if they turn out to
be nails and not fuses, it will be the melting appliance or the
appliance flex.
--
Adam
dennis@home
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:FNadnQui27l4RZHQ...@brightview.co.uk...
> On 18/12/2010 15:17, dennis@home wrote:
>>
>>
>> "Adam Wadsworth" <adamawayfromh...@gmail.com> wrote in
>> message
>> news:3a2efc2e-065a-48ad...@i41g2000vbn.googlegroups.com...
>>> On Dec 16, 8:18 pm, "dennis@home" <den...@killspam.kicks-ass.net>
>>> wrote:
>>>> "Man at B&Q" <manatba...@hotmail.com> wrote in
>>>> messagenews:646cacda-061d-47a7...@t35g2000yqj.googlegroups.com...
>>>>
>>>>
>>>> > Then you deserve all you get. You really ought to know better.
>>>>
>>>> And what about the poor suckers that have fuses from that batches that
>>>> didn't blow at the correct current, I suppose they deserve it to for
>>>> being
>>>> stupid enough to trust electricians with their lives?
>>>
>>>
>>> So how do you test these made up in your imagination fuses then?
>>
>> Well that would be the problem.
>
> Its pretty straight forward if you know anything about manufacturing
> processes. You pull out a sample of production on a regular basis and
> subject that to destructive testing against an agreed BS test procedure.
> If they fail to meet spec, you bin or rework that batch of production
> output.
Hence the asta certificate, there was a time when batch testing wasn't
mandatory.
Of course there may even be cases where the fuses are faked, sorry make that
we know there are cases where they have been faked.
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=25210&messid=193063&parentid=0&FTVAR_FORUMVIEWTMP=Single
Do you really want to continue stating that making the plug fuse essential
for safety is a good idea?
Andy Burns
But MCBs have been faked too
dennis@home
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:VrOdnS5MJ914SpHQ...@brightview.co.uk...
So you think its permitted to wire in a four way without any plug or FCU?
>
>> The plug fuse is a user serviceable part and is going to be abused, we
>> know it is abused.
>
> Is it equally easy to uprate your vacuum cleaner to 5kW for this non
> sequiter to have any relevance?
>
> Yes your could probably bodge a 4 way trailing lead and stick two 3kW fan
> heaters on it, but as has been observed in testing the lead will fail long
> before the fixed wiring is at risk.
You have no way to know this.
It is not difficult to find 2.5 mm flex and then there is no reason why it
should suffer any more than the fixed wiring.
There are even heat resistant flexes about that will suffer no damage at all
while the main cable melts.
The idea that something else will fail first is not reasonable unless that
something else is designed to fail first.
>
>> It also not tested. Virtually no PAT testing is done and even then they
>> seldom actually check the fuse is OK.
>> Electricians doing PIRs don't even care about the plug fuse despite it
>> being *essential* to protect the circuit they have just tested and
>> approved. The majority of householders don't even know its essential.
>
> You seem to think that plug fuses are designed to protect against
> overload, this is not the case. They are there for the fault protection of
> the flex connected to them. The common exception to this is with multiway
> extension leads, but this is not of relevance to the fixed wiring.
Oh don't start..
the whole argument is about the plug fuse protecting the spur from overload
and you know that.
If the 32A breaker provided protection to stop the spur being overloaded
there wouldn't be any argument as it would be designed as I want it to be.
>
> If we extend your argument to its logical conclusion, every table lamp
> ought to have a 4mm^2 flex so that it matches the trip threshold of the
> circuit breaker.
>
>> It is far more sensible to rate the breaker so that the cable is
>> protected whatever the householder does rather than saying well he would
>
> Which is exactly what the current circuit designs that permit 2.5mm^2
> cable on 32A breakers do. The breaker provides fault protection at all
> times. Overload protection some of the time.
But you just said the plug fuse doesn't protect the spur from overload so
now you think its OK to have part time protection.
Don't design anything I have to use if that is OK to you.
>
>> still be alive if he hadn't done something to the fuse in the plug.
>> Its like supplying a power press where the user has to fit parts to make
>> it safe.
>>
>>
>>> If overload protection is covered by another means then a 32A mcb will
>>> in most circumstances provide adequate fault protection to 2.5mm2
>>> cable. In fact there are situations where the use of 4mm2 cable
>>> INCREASES the risk under fault conditions. The reason is that the cpc
>>> conductor in 4mm2 cable is only 1.5mm2, so under fault conditions the
>>> touch voltage will be higher than with 2.5mm2 cable.
>>
>> That sounds more like a case to make the CPC bigger not to rely on the
>> consumer provided plug fuse to protect the circuit.
>
> It highlights why rings tend to perform better than radials with regard to
> earth faults. It also helps explain why when high integrity earthing is
> use on a radial circuit, it is done by turning the protective conductor
> into a *ring*
That's fine I haven't said you can't have a ring, just that the cables
shouldn't rely on it being a ring or to have spurs that need plug fuses to
prevent overload.
>
>> BTW AFAIK 32A radials are not the preferred radial, certainly not by me.
>
> A 32A radial in 4mm^2 T&E is a standard circuit. Just as is a 20A one in
> 2.5mm^2 cable. The 32A version is however far more useful as a general
> purpose socket circuit.
It is if you don't use 2.5 mm spurs anywhere.
If you do then you may as well use a ring as its no safer.
The 20A circuit doesn't rely on the plug fuse to prevent overloading the
cables like the others do.
dennis@home
"Andy Burns" <usenet....@adslpipe.co.uk> wrote in message
news:MpydnR0ye82FQpHQ...@brightview.co.uk...
> But MCBs have been faked too
>
> http://www.electriciansforums.co.uk/electrical-tools-products/18440-bbcs-fake-britain-fake-mcbs-far-east.html
>
True but there should be more chance of one being spotted by an electrician
than there is of the average person spotting a fake fuse. and they are
testable.
dennis@home
"dennis@home" <den...@killspam.kicks-ass.net> wrote in message
news:ieiqja$e8p$1...@news.datemas.de...
There is an article in switchedON (issue 18) that may well have a bearing on
this debate..
"The national standard for extension leads, BS 1363-2: 1995, specifies
a maximum 'continuous use' rating of 13 A for the fitted plug and
socket-outlet. The test current is set marginally above this at 14 A for
type-testing, to determine compliance with the product standard.
Standard BS 1362: 1973, covering the fuse link, requires the fuse to
operate at 1.9 times rated current (that is 24.7 A) within 30 minutes,
and also that the fuse shall have a non-fusing current of 1.6 times
rated current (that is 20.8 A).
It is therefore possible for an extension lead to carry a total current of
20 A for an indefinite period. While this may not be a common
situation, the product testing undertaken was to determine whether
it is possible to overload extension leads such that they might pose a
fire hazard."
Assuming they have the figures correct..
it is quite easy to get 40A out of a double spur for an indefinite period
using two fully working extension sockets and some loads.
This would probably trip an MCB before any serious heating of the cable.
However it means that you could draw 32A indefinitely, this exceeds the
rating if the 2.5 mm cable by a significant amount and it requires no
circuit modification at all, not even a faulty fuse.
The only question is which melts first, the flex or the cable and that
depends on what they are made of and how they are cooled.
So I guess I was wrong, you don't need a fault to overload the spur just an
ignorant user (most of the population at a rough guess).
John Rumm
>
>
> "John Rumm" <see.my.s...@nowhere.null> wrote in message
>>> It relies on the fuse in the plug to give overload protection to the
>>> spur.
>>> While this is fine in principle it isn't a good idea.
>>
>> That's not true, since there is no requirement for any fuse in the
>> spur - the spur could quite legitimately have an unfused flex outlet
>> on the end of it, and everything would remain well protected. The
>> overload protection of the spur being enforced by controlling the size
>> of the load - not by fusing, and the fault protection being maintained
>> at the origin of the circuit by the 32A MCB.
>
> So you think its permitted to wire in a four way without any plug or FCU?
No, an unfused spur can have a maximum of one single or one double
socket. I assume however you are referring to a 4 way trailing lead,
which is not designed to be "wired in" at all.
>>> The plug fuse is a user serviceable part and is going to be abused, we
>>> know it is abused.
>>
>> Is it equally easy to uprate your vacuum cleaner to 5kW for this non
>> sequiter to have any relevance?
>>
>> Yes your could probably bodge a 4 way trailing lead and stick two 3kW
>> fan heaters on it, but as has been observed in testing the lead will
>> fail long before the fixed wiring is at risk.
>
> You have no way to know this.
Actually I do.
Seen many extension leads with 4.0mm^2 flex?
Link?
> It is not difficult to find 2.5 mm flex and then there is no reason why
> it should suffer any more than the fixed wiring.
2.5mm^2 flex has a lower current carrying capacity than the fixed
wiring, and also is less likely to benefit from contact with masonry or
other building materials that will aid dissipation.
Commercial 4 way extension leads are almost exclusively wired with
1.5mm^2 flex however.
> There are even heat resistant flexes about that will suffer no damage at
> all while the main cable melts.
Clutching at straws dennis. If you are clued up enough to assemble an
extension lead with heavy gauge high temperature flex, you are also
unlikely to go replacing a fuse with a nail and plugging multiple fan
heaters into it. Assuming however for the sake of argument you do manage
to stick a sustained 40A load into a single socket, then its a pretty
safe bet the plug and or socket will give out before its supply cable.
> The idea that something else will fail first is not reasonable unless
> that something else is designed to fail first.
2.5mm^2 T&E with maximum current carrying capacity of 27A Vs cheap
thermoplastic 4 way socket (with dennis' patented nail in place of the
fuse) and 1.5mm^2 flex with a 15A max rating...
your call.
>>> It also not tested. Virtually no PAT testing is done and even then they
>>> seldom actually check the fuse is OK.
>>> Electricians doing PIRs don't even care about the plug fuse despite it
>>> being *essential* to protect the circuit they have just tested and
>>> approved. The majority of householders don't even know its essential.
>>
>> You seem to think that plug fuses are designed to protect against
>> overload, this is not the case. They are there for the fault
>> protection of the flex connected to them. The common exception to this
>> is with multiway extension leads, but this is not of relevance to the
>> fixed wiring.
>
> Oh don't start..
> the whole argument is about the plug fuse protecting the spur from
> overload and you know that.
That seems to be *your* argument, however its based on an incorrect
assumption.
The plug fuse is not there to protect the spur from anything; overload,
or fault current. Its there to provide fault protection to the appliance
flex, that is all.
> If the 32A breaker provided protection to stop the spur being overloaded
> there wouldn't be any argument as it would be designed as I want it to be.
I expect that most people want is a system designed to work and perform
safely in the real world. What we have evidently does so very well as
evidenced by our extremely low rate of accident and injury result from
fixed wiring.
If you want to do it differently, by all means do so, you don't need our
permission. However don't seek to justify this by making false claims
about proven engineered designs.
>> If we extend your argument to its logical conclusion, every table lamp
>> ought to have a 4mm^2 flex so that it matches the trip threshold of
>> the circuit breaker.
>>
>>> It is far more sensible to rate the breaker so that the cable is
>>> protected whatever the householder does rather than saying well he would
>>
>> Which is exactly what the current circuit designs that permit 2.5mm^2
>> cable on 32A breakers do. The breaker provides fault protection at all
>> times. Overload protection some of the time.
>
> But you just said the plug fuse doesn't protect the spur from overload
That's correct. It doesn't.
> so now you think its OK to have part time protection.
No, the design requires full time protection.
> Don't design anything I have to use if that is OK to you.
Well since I am only advocating the use of standard designs as
implemented up and down the country, with a long proven track record of
safety, its not going to be a choice you get to make other than perhaps
in your own home should you choose to rewire it.
However look on the bright side, many of the things I have designed are
intended to kill you, so you should be grateful for the remote
possibility that one might fail.
>>> still be alive if he hadn't done something to the fuse in the plug.
>>> Its like supplying a power press where the user has to fit parts to make
>>> it safe.
>>>
>>>
>>>> If overload protection is covered by another means then a 32A mcb will
>>>> in most circumstances provide adequate fault protection to 2.5mm2
>>>> cable. In fact there are situations where the use of 4mm2 cable
>>>> INCREASES the risk under fault conditions. The reason is that the cpc
>>>> conductor in 4mm2 cable is only 1.5mm2, so under fault conditions the
>>>> touch voltage will be higher than with 2.5mm2 cable.
>>>
>>> That sounds more like a case to make the CPC bigger not to rely on the
>>> consumer provided plug fuse to protect the circuit.
>>
>> It highlights why rings tend to perform better than radials with
>> regard to earth faults. It also helps explain why when high integrity
>> earthing is use on a radial circuit, it is done by turning the
>> protective conductor into a *ring*
>
> That's fine I haven't said you can't have a ring, just that the cables
> shouldn't rely on it being a ring or to have spurs that need plug fuses
> to prevent overload.
Which misses the fundamental point of the design in the first place.
i.e. that you can supply significant amount of power over a wide area,
using a cable that is easy to work with.
>>> BTW AFAIK 32A radials are not the preferred radial, certainly not by me.
>>
>> A 32A radial in 4mm^2 T&E is a standard circuit. Just as is a 20A one
>> in 2.5mm^2 cable. The 32A version is however far more useful as a
>> general purpose socket circuit.
>
> It is if you don't use 2.5 mm spurs anywhere.
Which would make no difference to performance since the load on each is
limited by the specification of only one single or double socket per
spur....
> If you do then you may as well use a ring as its no safer.
A 4mm^2 radial for general purpose sockets will in many circumstances
perform less well than a ring since it tends to have a higher earth loop
impedance. Its also more difficult to wire and in many cases saves no
copper. Hence why its fairly rare to see in practice.
> The 20A circuit doesn't rely on the plug fuse to prevent overloading the
> cables like the others do.
None of the standard circuits rely on plug fuses to prevent overloading.
dennis@home
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:qJWdnRxdvJ_H3pDQ...@brightview.co.uk...
> On 18/12/2010 16:31, dennis@home wrote:
>>
>>
>> "John Rumm" <see.my.s...@nowhere.null> wrote in message
>
>>>> It relies on the fuse in the plug to give overload protection to the
>>>> spur.
>>>> While this is fine in principle it isn't a good idea.
>>>
>>> That's not true, since there is no requirement for any fuse in the
>>> spur - the spur could quite legitimately have an unfused flex outlet
>>> on the end of it, and everything would remain well protected. The
>>> overload protection of the spur being enforced by controlling the size
>>> of the load - not by fusing, and the fault protection being maintained
>>> at the origin of the circuit by the 32A MCB.
>>
>> So you think its permitted to wire in a four way without any plug or FCU?
>
> No, an unfused spur can have a maximum of one single or one double socket.
> I assume however you are referring to a 4 way trailing lead, which is not
> designed to be "wired in" at all.
Earlier you stated "there is no requirement for any fuse in the spur - the
spur could quite legitimately have an unfused flex outlet on the end of it"
if so I can put a trailing socket on it.
>
>>>> The plug fuse is a user serviceable part and is going to be abused, we
>>>> know it is abused.
>>>
>>> Is it equally easy to uprate your vacuum cleaner to 5kW for this non
>>> sequiter to have any relevance?
>>>
>>> Yes your could probably bodge a 4 way trailing lead and stick two 3kW
>>> fan heaters on it, but as has been observed in testing the lead will
>>> fail long before the fixed wiring is at risk.
>>
>> You have no way to know this.
>
> Actually I do.
Actually you don't as you can't define the flex type or how it is cooled.
>
> Seen many extension leads with 4.0mm^2 flex?
I don't need 4 mm the spur is 2.5 mm so the flex would only need to operate
better than that.
>
> Link?
To what?
>
>> It is not difficult to find 2.5 mm flex and then there is no reason why
>> it should suffer any more than the fixed wiring.
>
> 2.5mm^2 flex has a lower current carrying capacity than the fixed wiring,
> and also is less likely to benefit from contact with masonry or other
> building materials that will aid dissipation.
>
> Commercial 4 way extension leads are almost exclusively wired with 1.5mm^2
> flex however.
>
>> There are even heat resistant flexes about that will suffer no damage at
>> all while the main cable melts.
>
> Clutching at straws dennis. If you are clued up enough to assemble an
> extension lead with heavy gauge high temperature flex, you are also
> unlikely to go replacing a fuse with a nail and plugging multiple fan
> heaters into it. Assuming however for the sake of argument you do manage
> to stick a sustained 40A load into a single socket, then its a pretty safe
> bet the plug and or socket will give out before its supply cable.
Clutching at straws John?
I can easily put 40A into a double spur without needing a faulty fuse as
ordinary 13A fuses will run at 20A continuous.
But according to you it fails to do that.
A 32A breaker can't protect 2.5mm T&E from overloads so what do you think
does?
>
>> Don't design anything I have to use if that is OK to you.
>
> Well since I am only advocating the use of standard designs as implemented
> up and down the country, with a long proven track record of safety, its
> not going to be a choice you get to make other than perhaps in your own
> home should you choose to rewire it.
Just remember that the regs are the bare minimum that the IEE thinks are
safe enough at the cost they have decided upon.
The OSG provides guidence for those that can't or won't do the maths to
prove what they do is OK.
You obviously don't understand the design compromises or what protects what
in the circuits.
I recommend you don't continue with this debate until you get a clue..
The fact that there is two sockets on a spur does not limit the current
below the cable rating.
It is quite obvious that it doesn't, you can even see it quoted in trade
magazines like switchedON issue 18 if you bother to loo;.
It is easy to get 40A continuously without blowing the plug fuses from a
double socket.
>
>> If you do then you may as well use a ring as its no safer.
>
> A 4mm^2 radial for general purpose sockets will in many circumstances
> perform less well than a ring since it tends to have a higher earth loop
> impedance. Its also more difficult to wire and in many cases saves no
> copper. Hence why its fairly rare to see in practice.
>
>> The 20A circuit doesn't rely on the plug fuse to prevent overloading the
>> cables like the others do.
>
> None of the standard circuits rely on plug fuses to prevent overloading.
Yes they do, you are wrong and refuse to accept that you are wrong.
You cling to straws and keep changing the argument just to avoid admitting
it.
You are also a hypocrite as you accuse other of doing the same, even when
they don't.
You only have to look at this post to prove that this is true of you.
If the circuits were protected by breakers upstream we wouldn't have this
debate and if you really have designed stuff you know that its illogical to
protect the cable at the wrong end using something the householder controls.
js.b1
#1 BS1362 : 1973 fuse standard:
- Fuse shall disconnect at 1.9x rated current in <30min (24.7A for
13A)
- Fuse shall have non-fusing current of 1.6x rated current (20.8A)
Therefore an extension lead with 13A plugtop fuse can provide 20.8A
non-fusing (indefinately).
#2 BS1363 double socket outlet:
- Each socket is protected by 13A plugtop fuse, 20.8A non-fusing
- Combined double socket load is 41.6A non-fusing
- Maximum continuous load for combined outlets is 19.5A (MK)
- Likely fire load for combined outlets is 24.5A (MK)
Therefore a 30A Final Circuit BS1362 fuse will non-fuse at 41.6A
(indefinately) and a 32A Type-B MCB will not-trip at 41.6A (for some
time).
Lets do a risk assessment.
Domestic installations tend to have multiple socket outlets (compared
to old fused multi-way adapters) and fewer extension leads. Where 4-
way extension leads are found they tend to supply audio-visual or
computer equipment which by its nature is relatively low current
demanding. At most it may supply a 2kW heater (8.3A), with the audio-
visual equipment becoming trivial in nature and overall the load is
within the 14A type testing limit.
Industrial installations are where there may be limited socket outlets
(big warehouse or lorry tyre shop) and 4-way adapters can be more
common in offices and such like. It is here that potentially someone
could plug two 2kW or two 3kW fan heaters into a multi-way adapter. It
is here, however, where a) fire is unlikely to trap people and b) fire
overnight is likely to only cause property damage.
So the only likely fire hazard really comes from kitchen fitters
plugging both dryer & washing machine into a 4-way strip adapter
shoved under a kitchen plinth, but due to the nature of a washing
machine element thermostat cycling (together with that of the dryer)
that still leaves the 4-way strip functioning within its limits.
Risk assessment not withstanding what is a simple solution?
#1 - Amend BS1362 to require 13A fuses to fuse at 16A not 20.8A.
#2 - Discontinue 13A fuses and replace by 10A fuses (fuse at 16A).
I am minded that stalled motor appliances, specifically fridge-
freezers & HVAC, do require 80-300A during startup. I suspect most are
limited to 80A (as PC SMPS) and a delay-restart to permit the internal
startup winding to cool down. Even so it is possible that switch-on
surge could cause a 10A fuse to fuse.
The simple solution to this is to make 10A fuses fuse at 1.6A but with
a slow-blow characteristic sufficient to permit high switch-on surge
appliances.
I think going forward that a very few fires could be avoided by use of
10A fuses, but in reality the bulk of fires it could prevent are in
the past. We are not in the 1950-1980 period with few socket outlets,
luxury of an electric cooker outlet with socket making that desperate
addition having exhausted the multi-way plug adapters for kettle
freezer toaster. There are a few such installations, but their Lead or
TRS fixed wiring is actually forcing upgrade to a safer number of
outlets - not to mention kitchen refits if only because the old 1950
unit has rotted into the ground.
That is the reality Dennis.
If you want to argue something useful, go test a 10A fuse on your
freezer & HVAC.
Andy Wade
> To be fair you are pretty screwed if the fuses are illegal copies from
> China with all the correct BS numbers stamped on them.
The irony here is that, AFAIR, the counterfeit fuses just lack sand
filling, so that, in all probability they'd operate OK in practice to
clear moderate overloads. Their real danger is that they explode and
arc if called on to break the full rated 6 kA fault. I suggest that
their danger has probably been somewhat overstated since (a) in 99+% of
cases the prospective fault current on a final circuit is far less than
that and (b) the upstream device will provide backup protection.
The counterfeit MCBs, OTOH, are *really* scary.
--
Andy
dennis@home
"js.b1" <js...@ntlworld.com> wrote in message
news:1436ac24-d8c0-4c5e...@j3g2000vbi.googlegroups.com...
Thanks for that description.
It actually agrees with what I said.
The protection isn't there and it relies on statistics and supposition.. the
user won't do this, the user wont do that, etc.,
if he does do it something else will probably fail (and kill him?) first.
The 10A fuse is probably a good idea, but not for heaters, fridges, etc. but
for the fourway strips. The 16A that it would fail at is more likely to
protect the flex than the 20A the 13A fuse will run at. You would have to
drop it to 8A to bring overload protection to the actual spur cabling.
Its pointless debating it with people that just quote the regs are the
answer when its the regs that are in dispute.
The evidence is that there is no overload protection for the spur and that
its easy overload it without introducing fault conditions and its only
assumed use that protects it.
I think the matter is closed.
js.b1
wrote:
> It actually agrees with what I said.
It does not.
It is a theoretical risk which is extremely unlikely to be realised.
More of a problem is substandard 4-way multi-adapters who struggle
with 10A continuous never mind 13A.
It could be solved with a minor amendment to a standard changing 13A
fuse spec to 1.25x (I suspect the 1.6x came about due to production
tolerances).
Adam Wadsworth
As bad as 2.5 for a fuse?
I went to a job this year where all the MCBs were 32A and the Zs was
18ohm (a neighbour had installed the CU). They has a fault on the
bathroom light (nice big burn marks on the ceiling) but somehow the
fault cleared.
--
Adam
Andy Wade
> On Dec 19, 12:53 am, Andy Wade<spambuc...@maxwell.myzen.co.uk> wrote:
>> The counterfeit MCBs, OTOH, are *really* scary.
> As bad as 2.5 for a fuse?
Yes, or worse:
http://www.voltimum.co.uk/news/9525/s/Counterfeiting-Alert.html
> I went to a job this year where all the MCBs were 32A and the Zs was
> 18ohm (a neighbour had installed the CU). They has a fault on the
> bathroom light (nice big burn marks on the ceiling) but somehow the
> fault cleared.
so much for Part P stopping such things. No RCDs in sight, presumably?
--
Andy
Adam Wadsworth
It was a "nice" metalclad CU with the tails passing through different
knockouts:-)
So again, it shows that you do not instantly die just because of a bad
setup even when there is a fault.
--
Adam