RCD for garage connection
Witchy
Got a socket and a couple of flouro tubes in the garage running off a
spur on the kitchen ring main, and I thought I was being clever by
buying a small MCB CU to connect it, so if anything happened to the
wire running to the garage the whole house wouldn't trip.
The bloke at the wholesalers insisted All Would Be Well, but it turns
out he was talking crap as the whole house will always trip before the
garage breaker goes off. Handy, particularly since the roof's
developed a drip (when the rain's blowing in the right direction) that
goes directly onto one of the lights :)
The house breaker is an MK LN5780 rated at 30mA tripping capacity and
2000A breaking capacity, so am I right in guessing that I need an RCD
for the garage that has a less than 30mA trip? And yes, I'm going to
get the drip fixed. *g*
cheers
witchy
Will Dean
news:u88t1v8n5io4ravs8...@4ax.com...
>
> The bloke at the wholesalers insisted All Would Be Well, but it turns
> out he was talking crap as the whole house will always trip before the
> garage breaker goes off. Handy, particularly since the roof's
> developed a drip (when the rain's blowing in the right direction) that
> goes directly onto one of the lights :)
>
> The house breaker is an MK LN5780 rated at 30mA tripping capacity and
> 2000A breaking capacity, so am I right in guessing that I need an RCD
> for the garage that has a less than 30mA trip?
Well, you can't have them the same, as you've discovered. The garage
supply should come from somewhere either without an RCD, or with a
slow-acting 100mA RCD.
You don't say how the overcurrent protection is done, but you might well
have similar discrimination problems with that.
Will
use...@isbd.co.uk
To get the discrimination you want (that is if the garage RCD trips
due to a fault then the house one doesn't) you have a few different
options but none is going to be particularly easy I don't think.
1 - Run the spur to the garage from a non-RCD protected circuit. This
assumes that you have a split-load CU in the house and that only
the downstairs ring main (and maybe some other circuits) are run
from the RCD protected section of the CU.
This will involve some more (longer) wiring but is probably the
best way to achieve what you want. You might even be able to add
a new circuit to your existing CU, is there space?
N.B. You *must* have the circuits in the garage protected by their
own RCD if you do this (locally in the garage CU or a new RCD in
the house CU, or an RCD spur). It's not clear from your posting
whether you have an RCD in the garage CU.
2 - Achieve discrimination by having a time delayed RCD in the house
CU and a normal one feeding the garage circuit. This solution
really only applies if you have a TT system in which case it's
really the same solution as above except that *all* circuits should
be protected by the time delayed CU. A time delayed (probably
100mA) RCD is *not* life saving and is not allowed for circuits
which may be used for portable appliances outdoors (i.e. a ring
main).
3 - A 10mA RCD in the garage *might* help but 10mA RCDs are hard to
get and would probably give you a lot of nuisance tripping. Also
there's no guarantee at all that a fault that trips the 10mA RCD
won't also trip the house 30mA RCD.
4 - Sort out the problem in the garage which is causing the trip,
regular tripping is indicative of a fault which should be fixed.
5 - If your whole house is protected by a single 30mA RCD then this
should be changed really, it's not allowed by current regulations
because of the risk of plunged into darkness by a minor fault.
If this is the cause of your problem then you need to address this
before sorting out the garage problem which will probably then be
sorted 'automatically' anyway.
We really need to know what sort of supply you have, what space there
is in the CU and what you have in the garage CU before being more
specific.
--
Chris Green (cgr...@x-1.net)
Andrew Gabriel
No. When daisy-chaining RCDs, it's the time delay which
tends to govern which trips first. The first thing that's
wrong here is that your whole house is on one 30mA RCD -
that doesn't conform to the regs (for precisely the reason
you've discovered). Really, you should sort that out.
Outdoor circuits should ideally not share RCDs (or MCBs)
with indoor circuits (although that isn't a requirement
of the regs).
> And yes, I'm going to
> get the drip fixed. *g*
That's not a bad idea anyway...
--
Andrew Gabriel
Witchy
>> The house breaker is an MK LN5780 rated at 30mA tripping capacity and
>> 2000A breaking capacity, so am I right in guessing that I need an RCD
>> for the garage that has a less than 30mA trip? And yes, I'm going to
>> get the drip fixed. *g*
>>
>You're going to find it a bit tough to fix this problem.
No change there then :)
>To get the discrimination you want (that is if the garage RCD trips
>due to a fault then the house one doesn't) you have a few different
>options but none is going to be particularly easy I don't think.
<snip, after careful reading>
>
>5 - If your whole house is protected by a single 30mA RCD then this
> should be changed really, it's not allowed by current regulations
> because of the risk of plunged into darkness by a minor fault.
> If this is the cause of your problem then you need to address this
> before sorting out the garage problem which will probably then be
> sorted 'automatically' anyway.
>
>We really need to know what sort of supply you have, what space there
>is in the CU and what you have in the garage CU before being more
>specific.
This is where puzzlement sets in. Both you and Andrew have said the
same thing so I'm beginning to wonder why myself. When we bought this
place 3 (eep) years ago we had an old meter and a 70s style 'button
pop' CU, and in between was this 30mA breaker. I wondered about its
presence particularly since none of the other houses I've lived in had
one.
I replaced the CU with a modern 10 way RCD protected unit with MCBs
for each circuit, and also separated the downstairs ring to give me a
separate kitchen ring as well as 2 new rings on the top floor (plus
lights - the top floor had nowt :).
Now then. the only time we've had a so-called electrician in this
place he put in such crap wiring it tripped the whole house (posted
that question here I think) instead of just tripping the circuit; when
I was extending the ground floor ring a few weeks ago, with the
circuit off at the CU, I managed to short live and earth....and the
whole house went off.
Should this be the case anyway or should *just* the circuit in
question trip? I remember this happening at the last house too, and
decided it was a 'feature' of the CU, so if I cut the upstairs
lighting circuit the house went off.
Thoughts?
cheers
witchy
David C
I've been looking at upgrading my own 1970s house, detached garage,
TN-S supply and descovered the following: (Much of it from the Hager
website).
As you discovered, RCDs can't be daisy chained. The 100ma RCDs are
really designed for "raised fire risk" properties (thatched etc) they
aren't classed as life saving so can't be used to protect POU sockets.
POU sockets are ordinary 13A sockets with potential for outside use,
that includes pretty much everything near a window so really all
downstairs ring main.
The answer is a split load consumer unit, in this half the outputs are
protected by a single 30ma RCD and half of them are not, of course
every circuit is protected by the MCB (which is really just an
electronic fuse). All lights are from the non RCD side, the spur to
the garage which is more prone to trip is from the non RCD side, best
solution then is to fit a combined RCD/MCB (called a RCCB) in the
consumer unit to protect this circuit, alternative is a small CU
containing the RCD and an MCB where the power goes into the garage.
Some people recommend that the freezer is from the non RCD side,
problem is this is difficult because quite often the freezer is in the
kitchen/utility and so the socket has POU.
Finally, Hager offer a module that plugs into the consumer unit that
displays current used, I like that so that's what I'm going for !
Hope that helps,
David C
Andrew Gabriel
avon...@totalise.co.uk.Removethisbittoreply (David C) writes:
>>> The house breaker is an MK LN5780 rated at 30mA tripping capacity and
>
> I've been looking at upgrading my own 1970s house, detached garage,
> TN-S supply and descovered the following: (Much of it from the Hager
> website).
>
> As you discovered, RCDs can't be daisy chained. The 100ma RCDs are
> really designed for "raised fire risk" properties (thatched etc) they
Actually, mainly where the earth fault loop impedance is too
high to guarantee that fault current protective devices (fuses
and MCBs) will trip within the required times. Generally, this
is the case where you have your own earth rod(s) - a TT system.
> aren't classed as life saving so can't be used to protect POU sockets.
>
>
> POU sockets are ordinary 13A sockets with potential for outside use,
> that includes pretty much everything near a window so really all
> downstairs ring main.
... unless you have dedicated outdoor sockets positioned such
that it is most unlikely anyone would use an indoor socket.
> The answer is a split load consumer unit, in this half the outputs are
> protected by a single 30ma RCD and half of them are not, of course
> every circuit is protected by the MCB (which is really just an
> electronic fuse). All lights are from the non RCD side, the spur to
> the garage which is more prone to trip is from the non RCD side, best
> solution then is to fit a combined RCD/MCB (called a RCCB) in the
^^^^
RCBO actually
(Residual Current Breaker with Overcurrent protection)
> consumer unit to protect this circuit, alternative is a small CU
> containing the RCD and an MCB where the power goes into the garage.
>
> Some people recommend that the freezer is from the non RCD side,
> problem is this is difficult because quite often the freezer is in the
> kitchen/utility and so the socket has POU.
If you think there is a risk of someone doing this, you could
use an incompatible 13A socket, or wire the devices in to an
FCU. A durable label warning the outlet is not RCD protected
and not suitable for outdoor equipment would be a good idea too.
> Finally, Hager offer a module that plugs into the consumer unit that
> displays current used, I like that so that's what I'm going for !
Interesting - these are usually rather expensive, as they are
mainly used in commercial/industrial settings. If the module
involves the use of a Current Transformer (CT), bear in mind
they can be rather dangerous (never leave the CT output
terminals disconnected from the measuring device, and always
ensure the current in the main conductor is switched off
when working on the CT circuitry).
--
Andrew Gabriel
Witchy
avon...@totalise.co.uk.Removethisbittoreply (David C) wrote:
>The answer is a split load consumer unit, in this half the outputs are
Bugger :) I only swapped this one a couple of years ago and we only
binned the old one today! Presumably a split load CU uses 2 rails
instead of just the one so I couldn't convert ours.
>protected by a single 30ma RCD and half of them are not, of course
>every circuit is protected by the MCB (which is really just an
>electronic fuse). All lights are from the non RCD side, the spur to
>the garage which is more prone to trip is from the non RCD side, best
All lights? Is this just 'because' or would it stop the circuit
tripping every time a bulb blows?
>solution then is to fit a combined RCD/MCB (called a RCCB) in the
>consumer unit to protect this circuit, alternative is a small CU
>containing the RCD and an MCB where the power goes into the garage.
That's what I fitted originally, just a single RCD and MCB.
>Hope that helps,
It does, ta. I'm loathe to swap CUs again though, but I may have to
'cos now that we've chucked all the crap out of the yard into a skip
the missus is already scheming about what she's going to do with our
75'x8' space, and some of those schemes involve lights........
cheers
witchy
use...@isbd.co.uk
> On Sat, 11 Jan 2003 13:17:50 GMT,
> avon...@totalise.co.uk.Removethisbittoreply (David C) wrote:
>
>>The answer is a split load consumer unit, in this half the outputs are
>
> Bugger :) I only swapped this one a couple of years ago and we only
> binned the old one today! Presumably a split load CU uses 2 rails
> instead of just the one so I couldn't convert ours.
>
>>protected by a single 30ma RCD and half of them are not, of course
>>every circuit is protected by the MCB (which is really just an
>>electronic fuse). All lights are from the non RCD side, the spur to
>>the garage which is more prone to trip is from the non RCD side, best
>
> All lights? Is this just 'because' or would it stop the circuit
> tripping every time a bulb blows?
>
points of having a split load unit to start with.
>>solution then is to fit a combined RCD/MCB (called a RCCB) in the
>>consumer unit to protect this circuit, alternative is a small CU
>>containing the RCD and an MCB where the power goes into the garage.
>
> That's what I fitted originally, just a single RCD and MCB.
>
Yes, but the RCD was 'in series' with the main house RCD and thus that
trips as well. With an RCBO (RCCB) on the non-RCD protectd sie of the
split load CU the garage RCD can trip without affecting the one
protecting the power circuits in the house.
>>Hope that helps,
>
> It does, ta. I'm loathe to swap CUs again though, but I may have to
> 'cos now that we've chucked all the crap out of the yard into a skip
> the missus is already scheming about what she's going to do with our
> 75'x8' space, and some of those schemes involve lights........
>
A new split load unit will only be about £60. Or you might find that
you can get a split load kit for your existing one, all that is
needed is a split busbar, an RCD to fit at the opposite end of the
unit from the main switch and some thick cables to feed the RCD. This
assumes your existing unit has space of course, the RCD is usually two
MCBs wide.
--
Chris Green (cgr...@x-1.net)
Witchy
>> All lights? Is this just 'because' or would it stop the circuit
>> tripping every time a bulb blows?
>>
>It's so the lights don't go out if the RCD trips, one of the major
>points of having a split load unit to start with.
Gotcha. I should've thought of that 'cos it's a right royal PITA when
the house trips when it's dark (no puns about it not being able to see
where it's going, please :))
>A new split load unit will only be about £60. Or you might find that
>you can get a split load kit for your existing one, all that is
>needed is a split busbar, an RCD to fit at the opposite end of the
>unit from the main switch and some thick cables to feed the RCD. This
>assumes your existing unit has space of course, the RCD is usually two
>MCBs wide.
Definitely no space then - all 10 spaces are used up. Mind, with the
possibility of the extra external lighting and the fact I still
haven't boxed in the wires from changing the CU over all those months
ago (far more important things to do and there's nowt dangerous
exposed) it might be worth thinking about swapping it *again*. <sigh>
:)
Presumably if I *do* decide to do this it'll be worth losing the
breaker that started this whole thread off in the first place and let
the CU do all the work?
cheers
w
use...@isbd.co.uk
>
>>A new split load unit will only be about £60. Or you might find that
>>you can get a split load kit for your existing one, all that is
>>needed is a split busbar, an RCD to fit at the opposite end of the
>>unit from the main switch and some thick cables to feed the RCD. This
>>assumes your existing unit has space of course, the RCD is usually two
>>MCBs wide.
>
> Definitely no space then - all 10 spaces are used up. Mind, with the
> possibility of the extra external lighting and the fact I still
> haven't boxed in the wires from changing the CU over all those months
> ago (far more important things to do and there's nowt dangerous
> exposed) it might be worth thinking about swapping it *again*. <sigh>
> :)
> Presumably if I *do* decide to do this it'll be worth losing the
> breaker that started this whole thread off in the first place and let
> the CU do all the work?
>
and RCD) for each circuit that requires RCD protection. That's
basically the ring mains (you don't *have* to protect the upstairs one
if it's separate but you might as well), electric shower if there is
one and any outside circuits such as garage. You don't then need a
split load unit. RCBOs are expensive though and many of them take two
MCB spaces per circuit (though there are exceptions to this).
If you go for the split load unit (cheaper) then the RCD protected
circuits are all supplied by one RCD and any fault will take them all
out. However since the lighting is on the non-RCD protected part of
the CU the lights don't go out.
A sort of half-way house set up would be to have a standard split-load
arrangement for the house and then a feed to the garage from the non
RCD protected side of the CU with an RCD in the sub consumer unit in
the garage.
--
Chris Green (cgr...@x-1.net)
Witchy
>The *ideal* way to do things is to have separate RCBOs (combined MCB
>and RCD) for each circuit that requires RCD protection. That's
>basically the ring mains (you don't *have* to protect the upstairs one
>if it's separate but you might as well), electric shower if there is
>one and any outside circuits such as garage. You don't then need a
>split load unit. RCBOs are expensive though and many of them take two
>MCB spaces per circuit (though there are exceptions to this).
I haven't got the physical rail space for any more MCBs so that's
pretty much out the window.
>If you go for the split load unit (cheaper) then the RCD protected
>circuits are all supplied by one RCD and any fault will take them all
>out. However since the lighting is on the non-RCD protected part of
>the CU the lights don't go out.
That's a hell of a lot better than the way things work now :)
>A sort of half-way house set up would be to have a standard split-load
>arrangement for the house and then a feed to the garage from the non
>RCD protected side of the CU with an RCD in the sub consumer unit in
>the garage.
So I'd still have to expand the CU anyway, since ATM the garage is off
a spur on the kitchen ring, which would be connected to the RCD side
of the CU, plus another feed for the external lights. Right. Sorted.
cheers Chris!
Owain
| So I'd still have to expand the CU anyway, since ATM the garage is off
| a spur on the kitchen ring, which would be connected to the RCD side
| of the CU, plus another feed for the external lights. Right. Sorted.
If you don't want to replace the CU you could consider adding a new 1 or 2
way switchfuse just to supply the outside circuits. This would be connected
to the meter tails between the meter and the existing CU using a service
splitter ("henley") block.
Owain
Witchy
wrote:
Ah right - I didn't know you could do that.....time to put me thinking
cap on then.
cheers
w