I need to install supplementary bonding in both kitchen and bathroom,
as there isn't any at all at the moment! Two queries arise please...
1. I have the luxury of having no ceiling at the moment in the room
below the bathroom, which means all the piping is readily accessible.
I could very easily install earth clamps connecting all the pipework,
very neatly and invisibly. However, is that allowed? Do you need to
be able to see the clamps etc in an installation? Where exactly do I
need to attach the clamps; as close as possible to taps/radiator etc?
2. I need to take an earth cable right through the house to the
kitchen sink. Do I need to have a separate, continuous cable going
from the earthing point at the fusebox all the way to the kitchen
(which means going through the bathroom en route) or is it sufficient
to piggy-back the kitchen earth cable on to a clamp on a bathroom tap,
Indeed, there isn't: and providing a 'better' (lower resistance) earth
connection for just *some* of the metalwork in the kitchen can make some
possible shocks *worse*, not better. Nor is there any need for the bathroom
bonding to go back to the main earth terminal. It's *supplementary* bonding,
designed so that all the exposed metalwork which either might become live or
provided some sort of path to earth is all held at the same electrical
potential, *even**if* a fault develops in any of the other earthing
arrangements. It's a *local* (to the bathroom) same-potential scene
you're trying to create, *not* one which is necessarily referenced to
the house earth. In practice it will be referenced to the house earth,
because much - probably all - of the metalwork you're cross-bonding is
already connected to earth, either through an "earth wire" if it's an
electrical fitting, or because it's connected to metal water pipes which
have a main bonding conductor from where the water main enters the house
to the main earthing terminal.
HTH - Stefek
Purely conjecture on my part, but these clamps have the same
functional specification as terminal blocks, do they not? A screw
compresses a cable etc.
If so, then surely BS7671 applies to these earth clamps in that they
should be accessible without major work.
Sending email to my published email address isn't
guaranteed to reach me.
Most I've seen seem to be fitted to the pipes rather than the taps
themselves. If you've got soldered joints, it seems to me they could go
anywhere reasonably close to the taps, since any high resistance is likely
to be between the pipe and tap, given the fibre washer employed and
usually some jointing compound.
I'm interested in this as I'm about to re-decorate the bathroom which has
no bonding at all, but I really don't want exposed clamps and cables to
the toilet cistern and bidet which have exposed pipes albeit at the back.
Also, how do you bond a cast iron bath which I don't think has any
provision for this? It's fully enclosed, so looks aren't a problem.
All my pipework is copper with solder joints where possible.
*Why do we say something is out of whack? What is a whack?
Dave Plowman firstname.lastname@example.org London SW 12
To answer the other question first...
The earth clamps need to be as close as possible to the taps, in order
to protect against the possibility that a section of plastic pipe might
be inserted somewhere in the pipe run. Obviously it will be better if
their location is hidden, yet still reasonably accessible.
To bond a cast iron bath, you should be thinking in terms of drilling
holes in the feet or legs, assuming these are solidly fixed to the
bath. A suitable nut and bolt will then allow an earth to be connected.
If separately mounted handles are fixed to the bath, these should also
be provided with an earth wire.
To quote from "Commentary on the IEE Wiring Regulations" (Paul Cook)
"There is particular requirement that the supplementary bonding itself
be carried out within the bathroom, simply that the parts themselves be
supplementary bonded. Supplementary bonding maybe installed underneath
floorboards, above ceilings or in an adjacent airing cupboard, as long
as it is accessible for inspection"
"Use can also be made of copper pipes as the supplementary bonding
conductor if the joints are electrically continuous"
Yes I think so.
Look at the drawings in the OSG, regs et al.
The bonding isn't all one piece of wire round everything.
There's a loop shower cpc - shower feed pipe - hot - cold - bath waste.
Another shaver point - sink hot - sink cold - sink waste.
Another radiant fire cpc - hot
Another cold - one side of radiator.
If, e.g, there was no shaver point & plastic waste to the sink, then I
don't believe there is a requirement for any bonding at the sink.
Hot & cold are link together by the bath loop, job done.
On 29 Jan 2004 15:09:35 -0800, email@example.com
You don't need to be able to see them, however they do need to be
You'll need to run a 10mm earth from your meter position to all of the
incoming supplies, gas, water, etc.. directly, no joining or
You''ll also need a 4mm earth around the pipes, radiator and all other
metallic surfaces in the bathroom.
And assuming your water supply is under the kitchen sink, you'll also
want to run a link across the hot and cold, (and sink if it's
metallic), in the kitchen.
There are some nice colouurful pictures on the web somewhere but I
can't seem to find them at this time!!
You should earth bond from the incoming electrical mains supply cable,
preferably into the Henley block or head block that is used to provide the
main earth to the consumer unit, and then on to the mains supply pipes of
both the water and the gas systems. This bonding should be provided using
10mm csa' (cross sectional area) Green/Yellow sheathed stranded conductors.
This bonding gives you a main earth bond to one end of the pipework on both
systems. Taking the shortest route is better because it saves on cable and
is safest because it provides the shortest path back to the main earth point
on the electrical supply.
The rest of the bonding to the pipework around the house is easiest done
where the pipes come together at the closest points where they come to the
taps or to one side of any metal radiators you have. You should also bond
together all the pipework around the hot and cold water storage tanks.
Making the connections at the closest points also helps to save cable and
gives fault currents the shortest path back to the main earth point at the
electrical supply. All the pipes which connect to the central heating
boiler, including the gas connection, should also be bonded together at the
closest point where they meet at the boiler. The boiler itself should
provide an earthing lug if the casing and chassis have exposed metal parts,
which most do.
All the supplementary bonding should be done using 4mm csa' Green/Yellow
sheathed cable to provide a low resistance path, and should be connected to
the pipework with proper earth straps, not just wrapped around the pipes,
and remembering to clean the pipes with wire wool or fine sand paper at the
point where the strap is to be positioned before putting the clamp around it
and tightening until the strap can not be turned or removed from its
position by accidental mechanical damage. The pipe cleaning helps the
earthing point make a good contact with the metal and it isn't trying to
work through any tarnish or gunge that might have built up on the pipes and
will increase any resistance in the pipework.
If any plastic pipework or joint fittings are used, then the earth bonding
should by-pass it and be connected to the metalwork where any valves or tap
connections have been made to all appliances, this includes all points on
the water and gas distribution systems.
Once you have a main earth point to one end of the main gas and water
supplies from the mains electrical supply, the supplementary bonding between
any gaps or breaks in the rest of pipework act in the same way as looping
everything together so that any fault current can take the shortest, lowest
impedance path back to main earth and cause the fitted safety devices to act
in a correct manner by quickly breaking the current flow to all parts of the
system that are affected by the fault.
Hope this helps answer some of your questions David. :-))
If plastic pipework (of 1m length or more) is used, then the taps/metal
bath/radiators etc. should NOT be supplementary bonded. Doing so reduces
electrical safety. If the internal pipework of the house is substantially
metal, but with a plastic supply (i.e. MDPE), then the internal pipework
should be main bonded.
On Fri, 30 Jan 2004 09:38:38 -0000, "Christian McArdle"
What about a steel bath where the taps are connected via long flexible
connectors, those flexible connectors surrounded by a nylon sheath.
Popular opinion suggests that the bath does not need to be bonded, and
I think that's right.
Sending email to my published email address isn't
guaranteed to reach me.
The implication of the IEE's advice is that if there is at least 1 metre of
plastic in the supply immediately before the tap it is OK not to bond.
However, it isn't really explicit about the length of insulating break
required, so I'd be a little circumspect in doing it just for 30cm of
insulated flexible pipe without further official advice. Perhaps a bit of
the concealed fixed pipework could be converted to plastic?
Obviously, if there's any chance of the metal bath being earthed by other
methods, such as nearby metal pipework that may touch it, or structural
metalwork, then things change and bonding would be required anyway.
Hmm, my Sime combi is certainly metal! but I can see no sign at all of
an earthing lug. There is a 3-core flex entering the boiler, but
having taken the boiler's cover off, I can see it dissappearing into
its bowels and I'd have to half-dismantle the boiler to trace where
the earth lead is wired to (possibly into the pump?) - surely that
shouldn't be necessary?
Think this is probably where I was getting confused (Stefek et al!)
abiut taking an earth bonding cable (10 mm2) all the way back to the
fusebox from the bathroom (or indeed the kitchen, if that's where the
water main comes in) ... from what you are saying above, isn't that
exactly what I'd need to do if there is any sign of plastic plumbing
being used (although that isn't the case here, in fact)?
Absolutely, thanks to you and the others for the advice!
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