I'm pretty well sorted now on the rewire (see earlier topic) but need
to brush up on Earth Bonding.
Question: Bonding in the kitchen and bathroon. I assume that this
involves ensuring that the Hot and Cold water supply to each sink,
bath and shower are bonded together but do I then run a cable from
both these areas (Kitchen & Bathroom) back to the consumer unit or can
I simply connect into the back of the nearest power outlet and what
size cable do I need to use...?
On Thu, 25 Oct 2007 08:39:55 -0700 someone who may be ac1951
Yes and no. Remember that a copper water pipe joined with real
joints (compression or solder) is at least as good at conducting
electricity as any likely size of bonding cable you may use.
Therefore there is no point in running umpteen bits of bonding cable
everywhere. As long as the pipes are bonded once that is enough.
Conversely plastic water pipe does not conduct electricity very well
(though the water inside pipes has been known to). In a house with
plastic pipework it is generally more dangerous to try and bond
individual metal taps than leave them unbonded.
Between these two situations is a grey area where what counts is
experience and begin able to argue with some bod who may not know
very much about what the Wiring Regulations actually say.
You need to connect it to the protective conductors of all circuits
which feed equipment in the room. This will certainly be the
lighting circuit concerned and perhaps some power circuits.
Sorry, it depends on a few factors. There is no one answer.
guide for BS7671, this has pretty pictures with instructions for bonding in
bathrooms - this is not required however when the 17th edition comes out
next year; but other safety factors are required for bathrooms - RCD
Well the first thing to get clear in your mind is the use of the
terminology. Many folks use "earth bonding" which is not really one
thing or the other.
You have Main Equipotential Bonding, and Supplementary Equipotential
Section 4.1 of the OSG gives you a run down on the requirements for the
"4.1 Main Equipotential Bonding of Metal Services (Figs 4a,
Main equipotential bonding conductors are required to 413-02-02
connect the following metallic parts to the main earthing
terminal, where they are extraneous-conductive-parts:
(i) metal water service pipes
(ii) metal gas installation pipes
(iii) other metal service pipes (including oil and gas supply
pipes) and ducting
(iv) metal central heating and air conditioning systems
(v) exposed metallic structural parts of the building
(vi) lightning protection systems."
(v) and (vi) are unlikely to apply in a domestic situation.
(iv) needs a little more investigation - see here for a previous
discussion on it:
Question: Bonding in the kitchen and bathroon. I assume that this
Kitchens do not need equipotential bonding (since it is assumed you are
less likely to be wet and naked in one!) - however they will frequently
be the place that the mains water service enters the house.
So basically you want to create a Faraday cage - such that in a fault
condition you would not be able to touch any two things with a
significant difference in potential. The actual potential itself is less
There is no need for a dedicated connection back to the main earthing
terminal. (but see below)
However, you should include in the equipotential bond the CPCs (i.e.
earth wires) of any circuits that deliver power into the bathroom.
Typically the lighting circuit, but also power and or shower feeds etc
if they are present. So in reality you will end up with a connection
back to the CU via the circuit CPCs, but there is no need for a
dedicated wire for it.
Main bonding conductors are typically 10mm^2 on TN-S or TN-C-S supplies,
and 6mm^2 on TT.
2.5mm^2 is adequate for equipotential bonds. (you may also use the CPCs
where appropriate - say for example an electric towel rail, it would
need no explicit connection other than via the heating elements earth
Note also that the 17th edition out next year, will change all this! ;-)
Andy Wade has published details in this group before. Not sure if there
are other online sources.
Basic summary for "special locations" the need for equipotential bonding
will go, however a requirement that *all* circuits used in the location
(i.e. including lighting) will need RCD protection.
In message , John Rumm
>> In message , John Rumm
>>> Note also that the 17th edition out next year, will change all this! ;-) >>> >>>
>> what are the changes going to be - is there an online description for them? >
>Andy Wade has published details in this group before. Not sure if there
>are other online sources.
>Basic summary for "special locations" the need for equipotential
>bonding will go, however a requirement that *all* circuits used in the
>location (i.e. including lighting) will need RCD protection.
MK and Contactum both do 10A RCBOs which would be suitable for lighting
circuits as long as they have no SES or micro bayonet fitting bulb
holders on them.
However remember that all circuits in a bathroom will need protection,
so if there are any power circuits (say feeding a towel rail or other
heater), one could use a larger sized RCBO to protect that, and then
derive the lighting from that circuit via a FCU in the bathroom.
Another option is a standalone RCD in a external 2 module enclosure.
This could be added to the output of any MCB for less than £20.
On Mon, 29 Oct 2007 02:16:19 +0000 someone who may be John Rumm
As separation of lighting and power circuits has been a feature for
a long time, to prevent lights going out if there is a fault on a
power circuit, this would be a backward step. A fault on a towel
rail should not plunge someone using a shower into darkness,
especially if that shower continues to work after the electricity is
This would obviously have to be a judgement call based on what equipment
you were sharing RCD protection with. A towel rail for example has a
very low trip risk. The same would apply to a shaver socket or extractor
fan (both of which would frequently be powered from the lighting circuit
A shower however would be a different proposition (most however will cut
the water flow if the power is removed). Although since RCBOs of
appropriate rating for showers and other power circuits are readily
available this is less of a problem.
On Mon, 29 Oct 2007 11:03:18 +0000 someone who may be John Rumm
Indeed. ISTM that the best way of complying would be to fit an RCD
to the part of the lighting circuit that feeds the bathroom. The
lighting would then only go off if there was a fault with that part
of the circuit. There might be a little array of them for the
various circuits, though in practice some of the RCDs might be at
the consumer unit.
For those who don't know, spur units with an RCD built in are
Hey John, extractor fans are the spawn of the devil and we should be
cautious about describing them as "low trip risk" appliances! ;-)
Seriously though, extractor fans have been identified as the culprit in
a number of house fires and should always be on a 3A (or lower) Fuse
with double-pole isolation, whether derived from a power or a lighting
 I have a reference for this, but can't find it. The subject has
certainly come up in uk.d-i-y before.
You may be confusing "low trip risk" with "low risk" - not the same
thing at all.
A low trip risk just means they are unlikely to cause significant earth
leakage and hence either cause a nuisance trip themselves, or sensitise
a RCD that may also be protecting another circuit. Many are double
isolated and have no earth connection and no metal casework. So their
direct contact risk is minimal.
That is all separate from their need for adequate over current and fault
current protection. This would be in comparison with something like an
electric shower for example, that has a high power electric heater that
may have high ish leakage. Hence sharing the RCD protecting one of these
with the main lighting circuit for the room would be far less sensible.