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...?
thanks Andy
On Thu, 25 Oct 2007 08:39:55 -0700 someone who may be ac1951 wrote this:-
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.
No.
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 protection.
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 Bonding.
Section 4.1 of the OSG gives you a run down on the requirements for the main bonds:
"4.1 Main Equipotential Bonding of Metal Services (Figs 4a,
4b, 4c) 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:
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 relevant.
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 connection.Note also that the 17th edition out next year, will change all this! ;-)
In message , John Rumm writes
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.
More here:
Just checked a few manufactures CU products and it appears that the smallest RCDO is 16A !! wonder if they're planning to launch a 6A version for use on Bathroom lighting circuits..
Andy
I expect they'll just put it on an FCU on a ring circuit. That also means you won't need a separate fan isolator anymore.
Only just caught up with this. If I ever find a way through Part P and my LA's BCO I had thought of using the 6A RCBO by Cubis - see
I'd welcome any views on whether Cubis are reputable/recommended.
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 wrote this:-
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 cut.
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 anyway).
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.
The 17th Edition of BS7671 due out next year is calling for RCD protection for all bathroom circuits and supplementary will not be required. Sockets will be allowed in zone 3.
On Mon, 29 Oct 2007 11:03:18 +0000 someone who may be John Rumm wrote this:-
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 available
On Mon, 29 Oct 2007 14:05:00 +0000 (GMT) someone who may be "Dave Plowman (News)" wrote this:-
A matter of personal prejudice.
Pass.
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[1] and should always be on a 3A (or lower) Fuse with double-pole isolation, whether derived from a power or a lighting circuit.
[1] I have a reference for this, but can't find it. The subject has certainly come up in uk.d-i-y before.
Hmm. You may not care about having non matching wiring accessories sticking out of the wall, but many would.
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.
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