Earth for kitchen sink
Liz
which was once connected to the copper pipe under the old sink has been left
hanging loose out of the wall. (God, I hope this means something to
someone, it sounds nonsensical to me)
I asked the guy who did the work but he was a bit vague about it, and
implied that it didn't really matter and that it would anyway be out of
sight once I've boxed the pipes in.
I understand that this is an earth and should be connected to the pipe, but
how do I fix it, what is its function, and what would happen if I don't fix
it back?
Thanks,
Liz
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Andy Hall
"Liz" <l...@leekfrith.fsnet.co.uk> wrote in message
news:a82r71$ld3$1...@news5.svr.pol.co.uk...
> I've had a new stainless steel sink fitted in a new position but the wire
> which was once connected to the copper pipe under the old sink has been
left
> hanging loose out of the wall. (God, I hope this means something to
> someone, it sounds nonsensical to me)
>
> I asked the guy who did the work but he was a bit vague about it, and
> implied that it didn't really matter and that it would anyway be out of
> sight once I've boxed the pipes in.
>
> I understand that this is an earth and should be connected to the pipe,
but
> how do I fix it, what is its function, and what would happen if I don't
fix
> it back?
>
> Thanks,
> Liz
>
If the pipe goes to the main stop tap, the wire should be connected to the
pipe near that tap using a special
earth clamp. You can get these from electrical wholesalers and some DIY
stores. They have a metal strap that goes around the pipe and a screw
clamp to tighten it. There will also be a label saying something like
"Safety Electrical Earth. Do not Remove".
There are schools of thought that say that the sink should also be bonded,
but this is not a wiring regulations requirement. You can make an argument
to do or not to do this particular connection.
.andy
Liz
"Andy Hall" <an...@hall.gl> wrote in message news:3ca4f64e$1...@nt1.hall.gl...
Many thanks, I'll go and get one of these clamps tomorrow if there are
regulations about it.
How important is this though? What's it protecting me from? What is it
earthing? The sink? The pipe? Why are they likely to cause electrical
shocks? And what does 'bonded' mean?
Sorry, I bet this is in the faq. I'll go and look now.
Liz
electrocuted
> should your sink somehow end up connected to the mains and what I just
> said.
>
> Respectively.
>
> :o)
>
> (Always assuming that (i) it is a green & yellow wire & (ii) the sink
> isn't earthed somewhere else.)
huge
thank you
respectfully
The Natural Philosopher
Liz wrote:
>
> Many thanks, I'll go and get one of these clamps tomorrow if there are
> regulations about it.
>
> How important is this though?
Almost completely unimportant.
> What's it protecting me from?
Dropping a food mixer in the sink, still plugged in, and touching the
sink, always assuming you have a steel floor in the house, and no eearth
leakage trip :-)
It goes back to teh days when wiring was poorly done in steel conduits
or not - with rubber insulation that perished. Lots of peple got shocks
all the time, and a few got killed. So they put a regulation in that
basically says, every piece of metal ought to be bonded (wrired)
together and earhed, so whatever metal thijngs you touch are at the same
potential as you are.
This is why when you pull off your nylon underwear, you get a shock when
you touch any metal..cos some buggers earthed it.
> What is it
> earthing? The sink? The pipe? Why are they likely to cause electrical
> shocks? And what does 'bonded' mean?
Any metal you might touch....is the idea..and they aren't likley to
cause electrical shocks...BUT...consider the scenario where your very
old electrif fire with its decaying cable is plugged into the socket
over he sing unit worktop, in order to dry out the cat or whatever.
The old cable chafes through, the live touches your sink...and every
single pipe/tap in the house is now 'live'. Because e.g. you have a
(new) plastic incoming water main...
If it wass all earthed, it wold just blow a fuse. If it isn't...it goes
live and stayes that way until you touch it...which *might* trip yoir
RCD, if you have one, and assuming its working...:-)
Its just another one of those 'well its not expensive, so why not insist
that its done, cos in the unlikely circumstance of several other things
not working as they should, it might save a life one day'
>
> Sorry, I bet this is in the faq. I'll go and look now.
>
>
Bitch! After all that erudite writing?
Liz
> > Sorry, I bet this is in the faq. I'll go and look now.
> >
> >
>
>
> Bitch! After all that erudite writing?
>
>
Even if it had been, I would still have been in need of your learned input,
the stuff in the faq generally presumes a certain amount of previous
knowledge, can't really deal with the basic idiot level of my questionings.
You lot always explain things clearly and usually in an unpatronising way.
Ta again.
L
Dave Plowman
Liz <l...@leekfrith.fsnet.co.uk> wrote:
> >
> Thank you NP, and it isn't in the faq, and I completely understand now.
> Even if it had been, I would still have been in need of your learned
> input, the stuff in the faq generally presumes a certain amount of
> previous knowledge, can't really deal with the basic idiot level of my
> questionings. You lot always explain things clearly and usually in an
> unpatronising way.
Heh heh - nicely put. Others wouldn't have been so polite. ;-)
I'd add that both the cold and hot pipes should be bonded with the
aforementioned earth claps - ask for 1/2 inch ones, and the cable isn't
meant to be jointed between the two. The insulation should merely be cut
off with a sharp knife and the cable wrapped round the first one before
going to the second. It's a bit of a fiddle under a sink.
--
* Never underestimate the power of very stupid people in large groups *
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Andy Wade
> Liz wrote:
> > How important is this though?
> Almost completely unimportant.
I beg to differ. In what follows I'm assuming that the errant wire in
Liz's kitchen is the 'main bonding conductor' that used to go to the
rising cold water main, under the sink.
> > What's it protecting me from?
> Dropping a food mixer in the sink, still plugged in, and touching the
> sink, always assuming you have a steel floor in the house, and no
eearth
> leakage trip :-)
It may do, but that's certainly not its main purpose. The purpose of
'equipotential bonding' (as it's called, technically) is to eliminate the
risk of dangerous electric shock due to voltage appearing between
different bits of metalwork. This can happen under certain (rare but not
unknown) electrical fault conditions.
For example, let's say that you have a (metal cased) electric toaster
which is placed such that you could have one hand touching it and the
other hand touching the sink. Now the toaster is earthed via its flex
and the normal electrical wiring, and that will prevent the appliance
itself becoming live if its own insulation fails. The sink on the other
hand, in the absence of 'bonding', might only be connected to earth via
the water pipework. The crux of the matter is that without the bonding
these two 'earths' (via wiring and via plumbing) are different and things
can happen that could cause them to have, in the worst case, almost the
full mains voltage between them, creating a very dangerous situation.
Note that this is nothing to do with the toaster being faulty, or to have
fallen into the sink while switched on, or indeed nothing to do with
anything being wrong with _your_ house electrics at all.
Equipotential bonding connects the different 'earths' together and
greatly reduces (effectively eliminates) the danger from this cause.
> It goes back to teh days when wiring was poorly done in steel conduits
> or not - with rubber insulation that perished. Lots of peple got shocks
> all the time, and a few got killed. So they put a regulation in that
> basically says, every piece of metal ought to be bonded (wrired)
> together and earhed, so whatever metal thijngs you touch are at the
same
> potential as you are.
You miss the point entirely. In the days of rubber-insulated wiring
there was no equipotential bonding as we now know it. The main reasons
for the high incidence of shock in those days were unshuttered sockets,
poorer appliance standards, and a general laxity about circuit earthing.
Those matters were all addressed in their own ways and things had
improved enormously by the time PVC-insulated cables came along (early
60's). Bonding came later, and the main driver was the introduction of
the protective multiple earthing (PME) supply system in the 70's. This
is basically a cost-saving measure for suppliers, as it does away with
separate earth conductors in the supply network. PME uses the neutral
conductor to provide the consumer with her electrical earth so -- here
comes the biggest risk -- if that neutral should happen to break between
your house and the substation then your earth will become rather live;
this is the fault I described in the toaster example above. With the
bonding in place _all_ your earths reach the same degree of liveness and
there is no danger -- you have created what is called an 'equipotential
zone'.
> This is why when you pull off your nylon underwear, you get a shock
when
> you touch any metal..cos some buggers earthed it.
You'll get exactly the same zap (for any large-ish metal items) whether
the metalwork is earthed or not. The capacitance to earth is what
matters here, and this is utterly irrelevant to the topic in hand.
> > What is it earthing? The sink? The pipe? Why are they
> > likely to cause electrical shocks?
The best way to think of it is that it's stopping the water pipe
'importing' an earth into your house that is different to the electrical
earth. That's why 'main bonding conductors' are connected at the point
of entry of the non-electrical services to the property. Gas and oil
pipes are bonded in a similar way, if present.
> > And what does 'bonded' mean?
Permanently and reliably connected, electrically, via conductors of
adequate size and sufficiently low resistance (impedance, if you want to
be pedantic).
> Any metal you might touch....is the idea..and they aren't likley to
> cause electrical shocks...BUT...consider the scenario where your very
> old electrif fire with its decaying cable is plugged into the socket
> over he sing unit worktop, in order to dry out the cat or whatever.
Surely these days you'd just put the cat in the microwave...
Seriously though, if anyone's read this far, I hope you can see that
bonding /is/ important. It's more important (essential in fact) if you
are in a PME supply. It's more important when the water and gas pipes
are metal. Supplementary bonding in bath & shower rooms (which we
haven't covered in this article) is very very important.
Happy Easter
--
Andy
Alan Shilling
Could I just confirm one thing though, if I have an RCD at the supply, does
that negate the need for earth bonding?
Alan Shilling
"Andy Wade" <spamb...@ajwade.clara.co.uk> wrote in message
news:01c1d84a$ccde8840$LocalHost@dog40...
> The Natural Philosopher wrote in article <3CA5514C.2090804@b.c>...
>
<Snipped to preserve electrons & bandwidth>
Dave Plowman
Andy Wade <spamb...@ajwade.clara.co.uk> wrote:
> For example, let's say that you have a (metal cased) electric toaster
> which is placed such that you could have one hand touching it and the
> other hand touching the sink. Now the toaster is earthed via its flex
> and the normal electrical wiring, and that will prevent the appliance
> itself becoming live if its own insulation fails. The sink on the other
> hand, in the absence of 'bonding', might only be connected to earth via
> the water pipework. The crux of the matter is that without the bonding
> these two 'earths' (via wiring and via plumbing) are different and things
> can happen that could cause them to have, in the worst case, almost the
> full mains voltage between them, creating a very dangerous situation.
> Note that this is nothing to do with the toaster being faulty, or to have
> fallen into the sink while switched on, or indeed nothing to do with
> anything being wrong with _your_ house electrics at all.
I'm not sure about this - it would require the toaster not only to be
faulty, but its earth to be disconnected as well. If its earth is ok, a
line to earth fault within it would simply take its fuse. And if this did
happen, having the sink at absolute earth can only make things *worse* if
you touch both of them at once. Unless, of course, the sink is connected
through a fault to another phase. ;-)
--
* Parenthetical remarks (however relevant) are (usually) unnecessary *
The Service Manager
>Thank you NP, and it isn't in the faq, and I completely understand now.
>Even if it had been, I would still have been in need of your learned input,
>the stuff in the faq generally presumes a certain amount of previous
>knowledge, can't really deal with the basic idiot level of my questionings.
>You lot always explain things clearly and usually in an unpatronising way.
>
Don't worry , my dad once went to repair a "wireless" set, which in those days
used to need an "aerial" and an "Earth", to find the earth connection ran to
a jam jar full of soil!
The Service Manager
Dave Plowman
The Service Manager <s....@miniac.demon.co.uk> wrote:
> Don't worry , my dad once went to repair a "wireless" set, which in
> those days used to need an "aerial" and an "Earth", to find the earth
> connection ran to a jam jar full of soil!
The earth on that wasn't for safety reasons, though, - indeed it might
have had a 'live' chassis if a universal type. It was to IIRC provide a
'ground plain' to the aerial.
--
* I'm already visualizing the duct tape over your mouth
Andy Wade
> Thanks Andy, best explanation I've ever heard!!
Thanks.
> Could I just confirm one thing though, if I have an RCD at the supply,
does
> that negate the need for earth bonding?
No, the RCD makes no difference at all since the danger can come from
external factors which cause the earths to be at different potentials.
--
Andy
Stuart
And where does plastic piping come in to the equation ???
Stuart
---------
Remove YOURPANTS before E-mailing Me
The Natural Philosopher
Andy Wade wrote:
> The Natural Philosopher wrote in article <3CA5514C.2090804@b.c>...
>
>
>>Liz wrote:
>>
>>>How important is this though?
>>>
>
>>Almost completely unimportant.
>>
>
> I beg to differ. In what follows I'm assuming that the errant wire in
> Liz's kitchen is the 'main bonding conductor' that used to go to the
> rising cold water main, under the sink.
>
>
>>>What's it protecting me from?
>>>
>
>>Dropping a food mixer in the sink, still plugged in, and touching the
>>sink, always assuming you have a steel floor in the house, and no
>>
> eearth
>
>>leakage trip :-)
>>
>
> It may do, but that's certainly not its main purpose. The purpose of
> 'equipotential bonding' (as it's called, technically) is to eliminate the
> risk of dangerous electric shock due to voltage appearing between
> different bits of metalwork. This can happen under certain (rare but not
> unknown) electrical fault conditions.
But your RCD will protect you theoretically against any current going
the 'wrong way' to erath..i.e. not through the neutral wiring..
>
> For example, let's say that you have a (metal cased) electric toaster
> which is placed such that you could have one hand touching it and the
> other hand touching the sink. Now the toaster is earthed via its flex
> and the normal electrical wiring, and that will prevent the appliance
> itself becoming live if its own insulation fails. The sink on the other
> hand, in the absence of 'bonding', might only be connected to earth via
> the water pipework. The crux of the matter is that without the bonding
> these two 'earths' (via wiring and via plumbing) are different and things
> can happen that could cause them to have, in the worst case, almost the
> full mains voltage between them, creating a very dangerous situation.
> Note that this is nothing to do with the toaster being faulty, or to have
> fallen into the sink while switched on, or indeed nothing to do with
> anything being wrong with _your_ house electrics at all.
Yes...but it would be hard for the sink to acquire a dangerously high
voltage at adequate current to be dangerous, wthout it being connected
in some way to the mains...and that is the point. Good earth bonding
stops the metal floationg at whatever potential local electrostatic
fields dictate, but in my opinion, more importantly, it gives a definite
route for any fault current to 'earth' so that faults instantly blow teh
RCD.
>
> Equipotential bonding connects the different 'earths' together and
> greatly reduces (effectively eliminates) the danger from this cause.
>
>
>>It goes back to teh days when wiring was poorly done in steel conduits
>>or not - with rubber insulation that perished. Lots of peple got shocks
>>
>
>>all the time, and a few got killed. So they put a regulation in that
>>basically says, every piece of metal ought to be bonded (wrired)
>>together and earhed, so whatever metal thijngs you touch are at the
>>
> same
>
>>potential as you are.
>>
>
> You miss the point entirely. In the days of rubber-insulated wiring
> there was no equipotential bonding as we now know it.
No, the meatl conduits were all the earths. And those were staked to -
normally either a dmaned good earth stake, or if a metal water pipe was
the way in for teh water. to that. WEhen plasic water mains came
in...it was the earth stale or nothing :-)
The main reasons
> for the high incidence of shock in those days were unshuttered sockets,
> poorer appliance standards, and a general laxity about circuit earthing.
Certainly all those things *caused* the problems, but lack of eathing as
you say, made it dangerous...because trips didn't blow lacking good earths.
> Those matters were all addressed in their own ways and things had
> improved enormously by the time PVC-insulated cables came along (early
> 60's). Bonding came later, and the main driver was the introduction of
> the protective multiple earthing (PME) supply system in the 70's.
I agree that is when the regulations came in...but my parents house
buldt in teh 50's and never rewired...has an earth wire from he incoming
water main to the fuse box...and another one to an earth stake. In those
days all plumbing and electrical work was in metal pipes, so that eerath
automatically carries through to the rest of teh house.
The introduction of plastic pipe, and indeed plastic in general as a
construction material for electrical goods has made it necessary o
rethink a lot of safety rules anyway.
This
> is basically a cost-saving measure for suppliers, as it does away with
> separate earth conductors in the supply network. PME uses the neutral
> conductor to provide the consumer with her electrical earth so -- here
> comes the biggest risk -- if that neutral should happen to break between
> your house and the substation then your earth will become rather live;
Yes, but all your electricity will fail anyway. With no neutral you will
get a whacking great resistance in the neutral circuit.
> this is the fault I described in the toaster example above. With the
> bonding in place _all_ your earths reach the same degree of liveness and
> there is no danger -- you have created what is called an 'equipotential
> zone'.
>
Which is basically what I said...
>
>>This is why when you pull off your nylon underwear, you get a shock
>>
> when
>
>>you touch any metal..cos some buggers earthed it.
>>
>
> You'll get exactly the same zap (for any large-ish metal items) whether
> the metalwork is earthed or not. The capacitance to earth is what
> matters here, and this is utterly irrelevant to the topic in hand.
>
Er...not necessarily..tho I see what you mean. If its earthed, ou get
the full static xcharge. If its capacittaively conected, you get a
proportion depending on *your* and *waht you touched* relative
capacitance to earth ...:-)
If ou like, a 'perfect' straight piece of wire has infinite capacitance
(and zero inductance and resistance) :-)
>
>>>What is it earthing? The sink? The pipe? Why are they
>>>likely to cause electrical shocks?
>>>
>
> The best way to think of it is that it's stopping the water pipe
> 'importing' an earth into your house that is different to the electrical
> earth. That's why 'main bonding conductors' are connected at the point
> of entry of the non-electrical services to the property. Gas and oil
> pipes are bonded in a similar way, if present.
>
>
>>> And what does 'bonded' mean?
>>>
>
> Permanently and reliably connected, electrically, via conductors of
> adequate size and sufficiently low resistance (impedance, if you want to
> be pedantic).
:-(
>
>
>>Any metal you might touch....is the idea..and they aren't likley to
>>cause electrical shocks...BUT...consider the scenario where your very
>>old electrif fire with its decaying cable is plugged into the socket
>>over he sing unit worktop, in order to dry out the cat or whatever.
>>
>
> Surely these days you'd just put the cat in the microwave...
>
> Seriously though, if anyone's read this far, I hope you can see that
> bonding /is/ important. It's more important (essential in fact) if you
> are in a PME supply. It's more important when the water and gas pipes
> are metal. Supplementary bonding in bath & shower rooms (which we
> haven't covered in this article) is very very important.
I think it is important, and for the sake of a few pence, its stupid not
to do it.
I really wanted to point out that of and by itself, the lack of bonding is not dangerous.
What is dangerous is that any OTHER electrical fault that might cause a bit of bare metal to go live, may go unnoticed by the rest of teh saftey equipment designed to detect it.
AND that, in certain circumstances, say a dozey RCD, and you touching a
live wire, touching an earthed bit of metal is far more deadly than
touching an unearthed one...
>
> Happy Easter
>
The Natural Philosopher
Andy Wade wrote:
There are very few external sources other than the mains input, that can
cause bits of metal to become dangerously 'live'.
I can't actually think of any, although of course you could - say -
construct a scenario where - say - the chassis of TV set is live with
respect to earth (in fact many were) BUT.
...in that case, unless you have an enormous TV, the power available
won't kill you.
So in general, all dangerous sources of shock are really from raw mains,
via whatever route they can find to the metal. AND if the metals is
earthed, such sources will blow teh RCD, and if not, they shold blow the
RCD when ou touch the metal, or if they don't, there is such a small
current that its not dangerous anyway...
Andy seems bent on constructiong weird scenarios to prove a point. i.e.
he is saying (internally) 'earth bonding is good, and here are the
reasons' whereas I am saying 'electricirty bcan kill you, but this is in
practice why it doesn't, and earth bonding is very good in some
cases...but mosly cos it helps trigger the RCD system under fault
conditions..and in some cases it could increase risk of shock.
I.e. I personally would rather be on hep pipe with no earths and a
plastic bath anywhere in a bathroom, when the psycho killer tosses the
hairdyer in next to me :-)
However, a fully bonded system wold just blow the RCD. asssuming the
psycho had'nt jimmied
it
>
Andy Hall
"Stuart" <stu...@shawsYOURPANTS2000.fsnet.co.uk> wrote in message
news:iqbgau856lfkfg4el...@4ax.com...
>
> And where does plastic piping come in to the equation ???
> Stuart
If you have a plastic water main coming into the house, then a stop tap,
then copper plumbing internally, there
must be a bond to the electrical earthing point near the consumer unit.
The same principle applies for gas.
If the incoming main is metal and internal plumbing plastic then a bond is
still required.
If both are plastic, then you can't really bond, except perhaps to put a
clamp on the brass stop tap.
Equipotential bonding for bathrooms and showers and other large exposed
metal areas are dealt with separately and
there are specific rules on what to do where there is plastic, copper or a
mix of the two. Basically bonding is required to the pipes near a bath,
basin,.... where connections are in copper.
The kitchen sink bond can be argued both ways - with and without bonding
there are scenarios where there can be a hazard, but in general the
principle should be to bond.
.andy
Dave Plowman
Stuart <stu...@shawsYOURPANTS2000.fsnet.co.uk> wrote:
> And where does plastic piping come in to the equation ???
It's a minefield, isn't it? At one time with all copper or lead pipework
including the incoming mains, there's a good chance the entire system was
pretty near earth and capable of carrying any earth currents likely to be
found enough to take out the fuse or breaker. But introduce a plastic
main, with the rest still copper, and a fault somewhere in the house could
*possibly* make it all 'live'. Of course, the immersion heater if fitted,
and possibly boiler *might* provide some form of earth path back to the
mains earth.
--
* I'm planning to be spontaneous tomorrow *
Martin Crossley
all I can find in the Regs is 413-02-12,which requires additional (local)
equipotential bonding only if there's a circuit supplying a socket-outlet
for a portable appliance which won't(because the earth-loop impedance is
just a littlle too high) cause the overcurrent protective device(probably a
rewireable fuse,looking at the graphs) to operate within 0.4s,but will in
under 5s.
(This would probably be mainly of use for a cooker control unit with
socket,on a circuit with a rewireable fuse,on a TN-S supply.)
I can't see any other requirement for it in a kitchen.
Of course,the normal main equipotential bonds ,as shown in the FAQ are
required,and if the water main is under the kitchen sink,it would be
reasonable to provide the main bond to the hot water pipes there as well.
(Andrew Gabriel-Help, please!)
Martin.
Andy Wade
> But your RCD will protect you theoretically against any current going
> the 'wrong way' to erath..i.e. not through the neutral wiring..
... and makes similar comments in article <3CA837EA.9060609@b.c>...
You continue (in both follow-ups) to miss the point completely. The main
purpose of bonding the incoming services is to protect you from the
consequences of faults _external_ to your installation which raise the
potential of the supplied earth relative to the surrounding ground, etc.
"Your RCD" OTOH will only protect you from faults within your
installation that result from phase to earth faults or leakage after the
RCD.
You go on to say that you can't think of any such circumstances (despite
the fact that I gave an example - broken neutral in a TN-C-S system) and
that I'm contriving all this to make a point. I refer you to the
Electricity Supply Regulations 1998, and in particular Section 7,
concerned with conditions which must be satisfied before a PME supply can
be given. Read it on-line at
http://www.legislation.hmso.gov.uk/si/si1988/Uksi_19881057_en_3.htm#mdiv4
There you will see that, by law, a supplier is not permitted to connect
the consumer's earthing conductor to the supply neutral (i.e. to give a
PME supply) unless the main equipotential bonding is present and correct
as set out in paragraphs 7(7) to 7(9). These amount to a re-statement of
the bonding requirements of BS 7671, but this time they are enshrined in
legislation.
I hope this helps to get the message across that equipotential bonding is
absolutely fundamental to the whole PME concept, which could be summed up
from the supplier's viewpoint as: "we offer to provide you with a earth
connection, but it might not actually be at earth voltage all the time.
"Don't worry though, this doesn't matter too much because you have to
bond all your other incoming services to our earth. "When you've done
that you won't get shocks off our earth because everything else that
might otherwise have introduced a different voltage is now tied to it.
"In fact this is so important that we can't legally give you this earth
at all until we've checked that your bonding is OK."
--
Andy
Bob
>
> I hope this helps to get the message across that equipotential bonding is
> absolutely fundamental to the whole PME concept, which could be summed up
> from the supplier's viewpoint as: "we offer to provide you with a earth
> connection, but it might not actually be at earth voltage all the time.
> "Don't worry though, this doesn't matter too much because you have to
> bond all your other incoming services to our earth. "When you've done
> that you won't get shocks off our earth because everything else that
> might otherwise have introduced a different voltage is now tied to it.
> "In fact this is so important that we can't legally give you this earth
> at all until we've checked that your bonding is OK."
>
> --
> Andy
I seem to have missed most of this thread through a combination of a dodgy
news server and my killfile, but I thought the following story might be of
interest.
My Dad noticed one day that he was getting shocks from the bathroom taps -
quite strong ones. He thought this strange since the pipework was bonded to
earth. During our investigations, we happened to open a junction box
feeding the electric shower, and found the insides to be charred, the wiring
insulation burnt off and the earth and live wires touching. However, no
fuses had blown because of this. Following the wiring back didn't reveal
any disconnected or wrongly connected wires. We came to the conclusion that
there must be a break in the earth wiring somewhere, and that the wiring for
the shower had been inadequate, causing it to overheat, burning through it's
insulation (although it was fitted 10 years ago).
The house was built in the 60s and has aluminium wiring. I seem to recall
reading that this kind of wiring degrades over a relatively short time - is
this correct?
I never understood why earth bonding of metal sinks etc is deemed essential.
It seems to me that if they were not connected to anything, no harm could
ever come of touching them. In fact, in the case I outlined above, the
earth bonding meant that an electrical fault made everything live - so we
would have been better off without it. We wouldn't have discovered the
fault I suppose, but I would rather not discover wiring faults by getting a
shock!
Bob
Andy Wade
> My Dad noticed one day that he was getting shocks from the bathroom
taps -
> quite strong ones. He thought this strange since the pipework was
bonded to
> earth. During our investigations, we happened to open a junction box
> feeding the electric shower, and found the insides to be charred, the
wiring
> insulation burnt off and the earth and live wires touching. However,
no
> fuses had blown because of this. Following the wiring back didn't
reveal
> any disconnected or wrongly connected wires. We came to the conclusion
that
> there must be a break in the earth wiring somewhere, and that the
wiring for
> the shower had been inadequate, causing it to overheat, burning through
it's
> insulation (although it was fitted 10 years ago).
So how did you stop the shocks from the taps?
> The house was built in the 60s and has aluminium wiring. I seem to
recall
> reading that this kind of wiring degrades over a relatively short time
- is
> this correct?
Yes, it can do. Aluminium conductors are no longer permitted for sizes
under 16mm^2, and even then must only be used with terminations
specifically approved for the purpose. The use of small sizes in
conjunction with normal brass screw terminals led to a rash of corrosion
problems and high-resistance connections, with all the dire consequences
that you can imagine that would follow (including fires).
> I never understood why earth bonding of metal sinks etc is deemed
essential.
It isn't, other than for supplementary bonding in bathrooms and shower
rooms -- and then only when the plumbing is in metal. There is
absolutely no requirement in BS 7671 to bond kitchen sinks, per se. Most
of this thread has been concerned with the main bonding of incoming
services, and the point of entry for the water service often just happens
to be under the sink, of course. However, it's the rising water main
that has to be bonded, not the sink.
--
Andy
Bob
>
> > I never understood why earth bonding of metal sinks etc is deemed
> essential.
>
> It isn't, other than for supplementary bonding in bathrooms and shower
> rooms -- and then only when the plumbing is in metal. There is
> absolutely no requirement in BS 7671 to bond kitchen sinks, per se. Most
> of this thread has been concerned with the main bonding of incoming
> services, and the point of entry for the water service often just happens
> to be under the sink, of course. However, it's the rising water main
> that has to be bonded, not the sink.
>
So why is it needed in bathrooms especially (where I thought you couldn't
have sockets, lightswitches etc)
Bob
Liz
whether to just box the thing in and forget about it, or to be so scared
that I'll never wash up again. Maybe I can get away with both.
Thanks, as usual, to all! I'm learning lots very fast....I think!
Liz
Andy Wade
> Well!!! As someone said, this is certainly a minefield.
It shouldn't be though. It is important and the rules and the guidance
provided in the On-Site Guide are very clear.
> I have no idea whether to just box the thing in and forget
> about it, or to be so scared that I'll never wash up again.
> Maybe I can get away with both.
No need for either. Just re-connect it. If in doubt get an electrician
in (quick Saturday morning cash job).
--
Andy
Andy Wade
> So why is it needed in bathrooms especially (where I thought you
couldn't
> have sockets, lightswitches etc)
Wet bodies -> low contact resistance -> increased risk of shock (much
more so than in the kitchen). Supplementary bonding in the bathroom ties
all relevant metalwork together and eliminates the risk of touchable
dangerous voltage differences.
--
Andy
Bob
Shock from what though? At the moment, the only thing I can think of would
be a shock from dodgy wiring connected to the sink!
Bob
C-H Gustafsson
Why should a kitchen sink or a bath tub be bonded to earth when a
knife or fork isn't?
Could somebody explain this: My desk at work has a plug with two
plastic pins and earth! A single wire connects it to the metal frame
of the desk. (All of the desks in the office seem to have this
feature.) How does connecting the desk to the socket outlet increase
safety?
Will this feature spread to other pieces of furniture? I'd hate having
my chair connected to a socket outlet...
/Clas-Henrik
Brian
"C-H Gustafsson" <esb...@hotmail.com> wrote in message
news:74f03cde.02040...@posting.google.com...
I dare say the electronics buffs will explain it in greater detail,
but basically it is stop static electricity from interfering with
sensitive electronics equipment, and or people.
Brian.
---
Outgoing mail is certified Virus & I.M of M Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
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Tim Mitchell
writes
>
>"C-H Gustafsson" <esb...@hotmail.com> wrote in message
>news:74f03cde.02040...@posting.google.com...
>>
>> knife or fork isn't?
>>
>> Could somebody explain this: My desk at work has a plug with two
>> plastic pins and earth! A single wire connects it to the metal frame
>> of the desk. (All of the desks in the office seem to have this
>> feature.) How does connecting the desk to the socket outlet increase
>> safety?
>>
>
>I dare say the electronics buffs will explain it in greater detail,
>but basically it is stop static electricity from interfering with
>sensitive electronics equipment, and or people.
>
risk of you getting an electric shock should it become live due to some
electrical problem (e.g. contact with live cable by it being trapped in
a drawer or something). The fault current would flow to earth through
the bonding and trip the RCD, blow the fuse or whatever, hence removing
the danger. Without the earth, the metal would remain live.
Such a fault could occur in a way that you wouldn't be aware of (until
you got a shock off it). If your knife and/or fork became inadvertantly
connected to mains live you would probably notice this before touching
them.... (Sorry, I am just having a disturbing vision of mealtimes with
all metal utensils earth-bonded on curly yellow cables...)
I presume your desk "earth" is a full earth connection, but if it's just
for anti-static purposes then there will be a 1Meg resistor in the earth
cable, and the plug will be connected with a "press-stud" type terminal.
This would not protect you from any stray live mains cables which
happened to be passing your desk, and unless your desk surface is anti
static as well, would be mostly pointless.
--
Tim Mitchell
Phil Addison
<l...@leekfrith.fsnet.co.uk> wrote:
>
>On Sat, 30 Mar 2002 05:46:52 +0000, in uk.d-i-y
>The Natural Philosopher <a@b.c> wrote:
>>
>>Liz wrote:
>> > Sorry, I bet this is in the faq. I'll go and look now.
>>
>>
>> Bitch! After all that erudite writing?
>>
>>
>Thank you NP, and it isn't in the faq, and I completely understand now.
It will be, if I get the time to add it .
... possibly under 'humour' (only joking)... I think.
--
Phil Addison
UK.D-I-Y FAQ http://www.diyfaq.org.uk/