Earth bonding on stainless-steel sink
Steve E.
Fellow DIY'ers,
I'm in the middle of fitting my new (Ikea) kitchen, part of which is a nice
little circular s/s sink (450mm diameter).
I know that the sink needs supplementary earth bonding (indeed there is a
sticker on it stating this) but there is no suitable tag onto which I can attach
an earth cable.
I will, of course, be earthing the mixer tap via its hot/cold water pipes, but
the tap is mounted on the worktop and not onto the sink itself - thus it won't
provide an earth to the sink.
Any suggestions as to the best way of attaching an earth?
TIA
Steve E.
Dave Plowman
Steve E. <ste...@no.email.please> wrote:
> Any suggestions as to the best way of attaching an earth?
If the sink is mounted in a non conducting worktop and has plastic waste
pipes, I can see no need to earth it. It is in effect just another lump of
steel in the kitchen, like a saucepan. But I'm sure I'm wrong.........
--
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Tony Williams
Dave Plowman <dave....@argonet.co.uk> wrote:
> In article <378b0436...@news.demon.co.uk>,
> Steve E. <ste...@no.email.please> wrote:
> > Any suggestions as to the best way of attaching an earth?
> If the sink is mounted in a non conducting worktop and has plastic waste
> pipes, I can see no need to earth it. It is in effect just another lump of
> steel in the kitchen, like a saucepan. But I'm sure I'm wrong.........
The regulation about grounding metalwork that a user
can touch comes from an unexpected but (imo) quite
reasonable direction. The thought is that if a live
wire accidentally connected to that metalwork then
a short occurs.... rather than that metalwork quietly
sitting there, live, an ambush for the next person
to come along.
This is certainly related to industrial equipment, but
I'm not up with the domestic Regs to know if this is
a blanket requirement for (say) the sink here.
(RCCB's..... best thing since sliced bread !)
--
Tony Williams.
Steve E.
wrote:
I have no problem with the idea of earthing the sink, whether or not it's
actually required by the regs (which I'm pretty sure it is). My problem is that
of how to actually get a decent electrical connection onto the underside of the
bowl. Short of using a bloody big jubilee clip I'm flumoxed.
> (RCCB's..... best thing since sliced bread !)
>
Nah. Phillippa Forrester is the best thing since sliced bread, followed by my
wife's chicken pie, Louise Nurding and then Tesco's Malted Milk biscuits.
RCCB's are certainly somewhere in the top 40 though, just behind Local Heros on
BBC2, and marginally ahead of silicone sealant. The chart is rounded off by
penguins at number 40 (they're cool).
Steve E.
Andy Wade
> I know that the sink needs supplementary earth bonding (indeed there is a
> sticker on it stating this) but there is no suitable tag onto which I can
attach
> an earth cable.
I presume this is the kitchen sink. Supplementary bonding is only mandated
by BS7671 in bathrooms and shower rooms. You often see it done in kitchens
though, and it can be a wise precaution. I think we should leave it to you
as a competent electrical engineer to decide for yourself whether to
bother. As to making the connection, have you seen Eze-earth clamps? (Ask
at any electrical wholesaler.)
--
Andy
Keith Wootten
>
>Fellow DIY'ers,
>
>I'm in the middle of fitting my new (Ikea) kitchen, part of which is a nice
>little circular s/s sink (450mm diameter).
[snip]
>Any suggestions as to the best way of attaching an earth?
If there's nowhere to drill a hole, then you could use conductive
(silver loaded I think) epoxy resin to bond a stud to the sink. It's
not cheap, though. Obviously the surface will need to be cleaned and
roughened, and the stud needs a nice big bonding area. Something like a
bolt through a perforated plate sounds good.
I suppose a spring or spring loaded strip could be used instead if
there's somewhere convenient to fix it. Maybe between the water pipe
and the sink?
Cheers
--
Keith Wootten
John Shotton
earthed. Supplimentary bonding is only required in a room containing a
bath or a shower, unless you fail to meet earth loop impedance
requirements, which with RCB is virtually inpossible (and very unlikely
even with circuit breakers)
Our village hall failed an inspection three years ago for no earth
bonding on kitchen sink. We instigated the appeal proceedure with the
contractors association and he was advised that, based on his report, he
had to give us a certificate as the earth bonding was not required by
the regs.
Earthed metalwork works both ways of course. If you come into direct
contact with electricity, the last thing you want is a nice low
impedance earth lying around. Where you are required to have
supplimentary bonding, eg in a bathroom, then all exposed metalwork must
be locally bonded together (though not necessarily to earth) even if it
is individually earthed so that a Faraday cage is created and it is
impossible to get a voltage difference between two pieces of exposed
metalwork. This will not protect you if you have a direct contact and
thus electricity within reach of people is banned. Lights on ceiling out
of touch, switch ditto with insulated pull cord, no sockets etc. Shaver
sockets are permitted but must include an isolating transformer. To
transfer the analogy to the kitchen would require the banning of all
electrical appliances
Steve E. wrote:
>
> Fellow DIY'ers,
>
> I'm in the middle of fitting my new (Ikea) kitchen, part of which is a nice
> little circular s/s sink (450mm diameter).
>
> I know that the sink needs supplementary earth bonding (indeed there is a
> sticker on it stating this) but there is no suitable tag onto which I can attach
> an earth cable.
>
> I will, of course, be earthing the mixer tap via its hot/cold water pipes, but
> the tap is mounted on the worktop and not onto the sink itself - thus it won't
> provide an earth to the sink.
>
> Any suggestions as to the best way of attaching an earth?
>
> TIA
>
> Steve E.
Steve E.
>The current edition of the regs do not require a kitchen sink to be
>earthed. Supplimentary bonding is only required in a room containing a
>bath or a shower, unless you fail to meet earth loop impedance
>requirements, which with RCB is virtually inpossible (and very unlikely
>even with circuit breakers)
>
>Our village hall failed an inspection three years ago for no earth
>bonding on kitchen sink. We instigated the appeal proceedure with the
>contractors association and he was advised that, based on his report, he
>had to give us a certificate as the earth bonding was not required by
>the regs.
>
>Earthed metalwork works both ways of course. If you come into direct
>contact with electricity, the last thing you want is a nice low
>impedance earth lying around.
I wasn't planning on coming into contact with it in the first place. The whole
point is to remove any mechanism by which any exposed live metalwork can persist
for longer than it takes a fuse to blow or an MCB/RCCD to operate.
>Where you are required to have
>supplimentary bonding, eg in a bathroom, then all exposed metalwork must
>be locally bonded together (though not necessarily to earth) even if it
>is individually earthed so that a Faraday cage is created and it is
>impossible to get a voltage difference between two pieces of exposed
>metalwork.
Not convinced about the Faraday cage bit but I'm with you on the touch voltages.
>This will not protect you if you have a direct contact and
>thus electricity within reach of people is banned. Lights on ceiling out
>of touch, switch ditto with insulated pull cord, no sockets etc. Shaver
>sockets are permitted but must include an isolating transformer. To
>transfer the analogy to the kitchen would require the banning of all
>electrical appliances
>
Good point, but you have to understand that most of the exposed metalwork in the
kitchen is /already/ pretty effectively earthed. The metal cases of ovens,
washing machines etc are all earthed - the radiator is essentially earthed (via
its pipes which are of course bonded to the house earth, and the taps are
more-or-less earthed (again via their pipes). The gas pipe to the boiler is of
course earthed.
Even the little screws on the plug sockets are earthed.
The only thing that's not is the sink. This is therefore (by my thinking) the
only exposed metalwork that could possibly represent any sort of a shock hazard,
and providing an earth for it is not in itself difficult - provided I can attach
it properly.
Maybe I'm being a bit over-zealous but ho-hum.
Steve E.
Dave Plowman
Steve E. <ste...@no.email.please> wrote:
> I wasn't planning on coming into contact with it in the first place.
> The whole point is to remove any mechanism by which any exposed live
> metalwork can persist for longer than it takes a fuse to blow or an
> MCB/RCCD to operate.
But you have to consider *how* it can become live. If there is no
conductor attached to it this is impossible. Earthing it just might
present a real life hazard that didn't exist before. Your choice....
Charles (Joe) Stahelin
<ajw...@dial.pipex.com> writes
>I presume this is the kitchen sink. Supplementary bonding is only mandated
>by BS7671 in bathrooms and shower rooms. You often see it done in kitchens
>though, and it can be a wise precaution. I think we should leave it to you
>as a competent electrical engineer to decide for yourself whether to
>bother. As to making the connection, have you seen Eze-earth clamps? (Ask
>at any electrical wholesaler.)
What about putting a large steel or copper washer up against the metal
on the underside of the sink on one of the tap lines. An earth cable
could be soldered or otherwise attached to the washer
--
Charles (Joe) Stahelin,
Huddersfield, West Yorkshire, UK.
Steve E.
wrote:
>In article <378b579c....@news.demon.co.uk>,
> Steve E. <ste...@no.email.please> wrote:
>> I wasn't planning on coming into contact with it in the first place.
>> The whole point is to remove any mechanism by which any exposed live
>> metalwork can persist for longer than it takes a fuse to blow or an
>> MCB/RCCD to operate.
>
>But you have to consider *how* it can become live. If there is no
>conductor attached to it this is impossible. Earthing it just might
>present a real life hazard that didn't exist before. Your choice....
>
Are you seriously suggesting that appliying a solid earth to the sink might
itself provide a mechanism by which the sink can become live? Well, it's an
interesting point of view ....
Steve E.
Dave Plowman
Steve E. <ste...@no.email.please> wrote:
> Are you seriously suggesting that appliying a solid earth to the sink
> might itself provide a mechanism by which the sink can become live?
> Well, it's an interesting point of view ....
I have indeed come across a house where /all/ the pipework was way above
earth.
But I really cannot see any point in earthing something which has no
chance of permanent connection to anything dangerous. Remember it is a
steel sink in a wood? worktop with no taps in contact with it. What
possible reason is there for earthing it? Imagine one scenario. The sink
is earthed and you pick up a faulty appliance while touching it. Result?
Shock. And things like kettles are one of the most likely appliances to
have damaged mains leads through proximity to hot cooker rings, and much
movement etc.
All this is based on experience in my workshop, where I never earth
things *unless* required. I prefer to 'float' at 240v occasionally with as
little as possible around me that might complete the circuit........
Andy Wade
> What about putting a large steel or copper washer up against the metal
> on the underside of the sink on one of the tap lines. An earth cable
> could be soldered or otherwise attached to the washer
That sounds like hard work compared to using an eze-earth clamp, which will
fit over any available short metal edge - the turned down edge of the sink,
maybe. For those not familiar with them, these clamps consist of a short
length of small metal channel section, and a socket head grub screw, which
does the clamping. Connection (6mm^2 max) is made with an ordinary
insulated crimp tag (the ring type) which is supplied as part of the kit.
Very handy for making electrical connection to all manner of metal objects,
and, as I said before, readily available.
--
Andy
No connection with ... (& pun fully intended)
John Shotton
>
> In article <378c4302....@news.demon.co.uk>,
> Steve E. <ste...@no.email.please> wrote:
> > Are you seriously suggesting that appliying a solid earth to the sink
> > might itself provide a mechanism by which the sink can become live?
> > Well, it's an interesting point of view ....
Not at all, but it does provide a very low impedance path for the fault
current if you should happen to touch it whilst in contact with a source
of electricity
>
> I have indeed come across a house where /all/ the pipework was way above
> earth.
>
This is one example of where you do not want to earth exposed metalwork.
Though pipework is copper, there is often PTFE at joints, so the water
pipe system is not necessarily a low impedance to earth. Lets say that
somewhere in the house a live conductor connects to a water pipe and the
resultant current is not sufficient to trip the breaker. A person then
comes into contact with the pipe system, eg touches a radiator. A
current will flow through him/her the magnitude of which will depend
upon how well he is earthed. If they are also in contact with a well
earthed sink, the current will be higher.
Earthing works well if you are at the same time isolated from possible
touch, eg in a bathroom. The appliances in a kitchen are usually totally
enclosed in metal which is earthed so that an internal fault cannot
appear on the outside of the appliance.
In the case of the kitchen sink, if a metal kettle, which is still
plugged in, develops a fault then it should trip the breaker via its own
earthed metalwork, in which case it is irrelevant as to whather the sink
is earthed or not. If however the earth circuit on the kettle is faulty
so that insufficient fault current flows to trip the breaker, then if
the sink is earthed a much larger current will flow through a person
when they, for example, contact the sink (or more likely the tap) with
one hand whilst holding the kettle in the other. In this scenario it is
safer to not have the sink earthed. safest of all is a plastic sink and
taps.
The requirements for a bathroom are that all exposed metalwork be bonded
together. It does not call for this to be earthed. the regs say that
this is to ensure that there can not be a potential difference between
any exposed metalwork. Hence the requirement for fat cable irrespective
of the circuit ratings in the bathroom
Tim Dean
have a big swa termination.(or just take the plastic outlet)
----------------
| |
| |
-----------------
| |
| |
measure the diameter of the outlet and purtchase a banjo earth tag to fit
over the outlet. (or you could make one)
Then crimp a earth lead(s) to the banjo with a crimp tag. Use 4-6mm cable.
Tip.Using a length of t+e pull the earth core out and crimp the red and
black cables to tags and bolt them to the banjo.The other ends can then goto
the hot and cold water pipes .That way the cable will be neat.Use a bit of
green and yellow tape to indicate the earthing conductor.
Roughen up the banjo and the sink for good contact.
fasten with the nut on the sink connector.
Hope that this helps
tim
--
__ __ __ __ __ ___ _____________________________________________
|__||__)/ __/ \|\ ||_ | /
| || \\__/\__/| \||__ | /...Internet access for all Acorn RISC machines
___________________________/ td...@argonet.co.uk
http://www.argonet.co.uk/users/tdean
... I forgot my tagline file...
Tony Williams
Keith Wootten <Ke...@wootten.demon.co.uk> wrote:
> I suppose a spring or spring loaded strip could be used instead if
> there's somewhere convenient to fix it. Maybe between the water pipe
> and the sink?
The thing about earth connections is that their
conductivity must remain at a safe low level, right
throughout their period of service (of many years).
The normal connection will be some sort of piercing
and clamping arrangement, where the actual point(s)
of contact are gas-tight. Gas-tight is a magic phrase,
because it is this that prevents the buildup of oxides
or corrosion products that can degrade the conductivity
of the joint.
--
Tony Williams.
Keith Mendum
>
[snip]
> The thing about earth connections is that their
> conductivity must remain at a safe low level, right
> throughout their period of service (of many years).
> The normal connection will be some sort of piercing
> and clamping arrangement, where the actual point(s)
> of contact are gas-tight. Gas-tight is a magic phrase,
> because it is this that prevents the buildup of oxides
> or corrosion products that can degrade the conductivity
> of the joint.
The recommended eze-earth clamp has a serrated screw to make contact
with the object and a similar shakeproof washer to hold the crimp tag.
--
Regards,
Keith
Clive
can find a lip to attach them to. They are also known as Radiator Earth
Clamps BTW, for the bathroom rads; also used for earthing trunking,
suspended ceilings, metal work-surfaces etc.
If no lip, I just wondered how the s/s sink is held in the worksurface - if
by clamps could these provide the connection? I don't particularly like
this idea but you might be desperate! However this solution, like the
copper washer idea, could become loosened during use or maintenance, whereas
a dedicated connection (with shakeproof washer) is unlikely to come undone
accidentally.
The jubilee clip idea is not so far fetched - it might be possible to modify
a standard plumbing earth clamp to use a big band of thin steel.
--
Clive c...@jumbojet.uk (drop the elephant to reply)
My views, not my employer's.
Clive
>If however the earth circuit on the kettle is faulty
>so that insufficient fault current flows to trip the breaker, then if
>the sink is earthed a much larger current will flow through a person
>when they, for example, contact the sink (or more likely the tap) with
>one hand whilst holding the kettle in the other. In this scenario it is
>safer to not have the sink earthed.
Can anyone resolve the above dilemma? Imagine the situation where the earth
lead of a metal-cased kettle has become disconnected: The metal case could
float up to near full mains potential but no protective device would trip.
And to quote from John Whitfield's Electrician's Guide to the 16th ed Wiring
Regs (ISBN 0 9517362 6 4):
"Thus if the resistance between the metalwork and the general mass of earth
is low enough to permit the passage of a dangerous shock current, then the
metalwork must be bonded."
It goes on to calculate some resistance values (25-50kohm) above which
bonding is not required (and by implication values below which bonding _is_
required). This suggests to me that the resistance to ground is made lower,
the current is made higher, and the so danger is made greater by
supplementary bonding.
--
Clive c...@jumbojet.uk (drop the elephant to reply)
My views, not my employer's.
UK.D-I-Y FAQs are archived at http://www.axp.mdx.ac.uk/~john49/faq0.htm
Andy Wade
> John Shotton wrote ...
> >If however the earth circuit on the kettle is faulty
> >so that insufficient fault current flows to trip the breaker, then if
> >the sink is earthed a much larger current will flow through a person
> >when they, for example, contact the sink (or more likely the tap) with
> >one hand whilst holding the kettle in the other. In this scenario it is
> >safer to not have the sink earthed.
>
> Can anyone resolve the above dilemma? Imagine the situation where the
earth
> lead of a metal-cased kettle has become disconnected: The metal case
could
> float up to near full mains potential but no protective device would
trip.
Most design for electrical safety is based on the 'single fault principle'
- i.e. safety should be maintained in the presence of any single fault
(together with other faults which follow as a logical consequence of the
first). This principle is embodied in all domestic appliance standards,
and in BS 7671 (the wiring regs). However, what is being postulated in
this thread is the presence of two _independent_ faults - broken 'earth'
connection to the kettle, together with failure of its basic insulation.
This _will_ give rise to a dangerous situation - live kettle - because the
kettle is faulty _and_ the wiring is faulty. The problem, if there is
one, is that the o/c earth fault could exist and go undetected for a long
time - until the second fault occurs, in fact. This is good illustration
of the need for thorough testing of new wiring, and for routine appliance
testing ('PAT testing'). So the real point isn't whether or not the sink
should be 'earthed' but that the kettle body should not become live (for
more that the permitted 400ms disconnection time) in the first place.
However, let us suppose that it does. As stated, you would be safer if
nearby metalwork (extraneous-conductive-parts in BS 7671 terminology) was
left floating. The problem is that you couldn't in practice assume that a
sink was floating simply because it wasn't directly earth bonded with its
own wire. There may be a connection via the taps and plumbing, for
example. Special or unusual measures like insulating washers under the
taps aren't foolproof either - you don't expect a plumber who turns up to
replace a tap to know why they're there [1].
There are two effective measures that you can adopt though, if you are
worried about being electrocuted by your kettle. Firstly, install a 30mA
RCD in the supply to the kitchen sockets. (Some will say that you may get
nuisance tripping due to earth leakage in mineral insulated heating
elements, although I've never found this to be a problem.) Secondly, use
a plastic bodied kettle (still Class I - but only the element inside is
live if our two faults are applied). As it happens both of these apply in
my own kitchen, although I can't remember ever being worried about being
fried by the kettle.....
[1] BS 7671 does allow the use of special methods of protection from
indirect contact [2] as alternatives to the usual EEBADS [3]. One of
these is "protection by non-conducting location" which amounts to
preventing simultaneous body contact with different metal items and using
insulating walls and floor. Such measures are for special application
only, and have to remain under the supervision of an electrical engineer;
they certainly cannot be entertained for domestic use. In fact I have
never seen any of them used.
[2] I.e. contact with a part which is live as the result of a fault.
[3] Earthed equipotential bonding and automatic disconnection of supply.
--
Andy
Dave Plowman
Andy Wade <ajw...@dial.pipex.com> wrote:
<snip>
> The problem is that you couldn't in practice assume that a
> sink was floating simply because it wasn't directly earth bonded with its
> own wire. There may be a connection via the taps and plumbing, for
> example. Special or unusual measures like insulating washers under the
> taps aren't foolproof either - you don't expect a plumber who turns up to
> replace a tap to know why they're there
Coming back to the original question!!! the steel sink is *not* connected
to the taps. If it *were* with copper pipes and or a conducting waste,
then IMHO, it should be earthed.
Clive
Thank you for the comprehensive reply, Andy. The faulty kettle scenario is
perhaps a bit or a red herring but I was just trying to imagine _any_ reason
for the supplementary bonding of the kitchen sink to ground when the fault
scenario involves an indirect contact from live, through a human body, to
the sink. The Whitfield book I quoted from assumes the above mechanism and
suggests bonding as the solution. This book is in widespread use (commonly
available from electrical wholesalers, TLC, Maplin etc) so it is not just
some quirky text. His justification for bonding the sink has always seemed
ridiculous to me but I'm not an expert and I hoped someone could offer some
expert explanation.
If the sink could conceivably become directly connected to live then the
reason for bonding it to earth is pretty obvious.
Andy Wade wrote in message <01bed0f4$780d7ca0$LocalHost@dog40>...
> The problem, if there is
>one, is that the o/c earth fault could exist and go undetected for a long
>time - until the second fault occurs, in fact. This is good illustration
>of the need for thorough testing of new wiring, and for routine appliance
>testing ('PAT testing').
And justifies the thorough testing of old wiring too. In particular, faulty
ring mains go unnoticed for far to long in my opinion.
Steve E.
Well, this all turned out to be more interesting than I was originally
expecting. Thanks for all the input.
Not really sure what to do about earth-bonding - but since I'm having difficulty
finding a suitable connection point on the sink, and given that bonding isn't
required by the regs anyway - I think I'll do without.
Thanks again for all the help.
Steve E.