Bonding in bathrooms


Postby buzbydiy » Mon Feb 07, 2011 7:29 pm

I have gutted my bathroom, Iam at the stage where pipes are accessible. When I stripped the old suite out - there was bonding on the radiator by means of a clamp at the bottom of it ..... as well as cross bonding on the hot & cold of the basin. Nothing on the bath.
My main questions are - as I am at a stage to do something about it is:-
1. How 'extensive' do I bond pipework. I presume I need to cross bond hot & cold of bath & basin & cold feed for the toilet where they are out of the floor.
I am fitting a chrome finished towel warmer, [ not electrically heated ]. Though it said nothing in the instructions will I have to put a clamp say on one of the rungs, and will I also need to bond the supply and return pipes to it as well. In other words. Would I need three points of bonding ? ? ?
2. I will have a ceiling light that has a chrome finish, and a Shaver socket in the room. Do I need to run a seperate 4mm earth lead from these appliances to a pipe within the bathroom, or is the electrical earth sufficient ? ? ?
An additional question if I may. I am fitting a thermostatic bar valve shower unit on the wall above the bath, [ so bath can be used as a shower ] which has its hot & cold tee'd off the bath hot & cold. Will bonding the shower beyond the 'tee' - be enough to bond the chrome bar valve. Distnce from tee to valve is 4ft, or do I have to bond the bar valve as well.
I don't mind what ever I need to make my family safe, but could do with some clarity please.
Regards,
PS
Thanks to 'ericmark' for advice. Think I may have confused someone else's plight with mine - sorry.
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Postby ericmark » Tue Feb 08, 2011 10:20 am

701.415.2 Supplementary equipotential bonding
Local supplementary equipotential bonding according to Regulation 415.2 shall be established connecting together the terminals of the protective conductor of each circuit supplying

Class I and Class II equipment to the accessible extraneous-conductive-Parts, within a room containing a bath or shower, including the following:
(i) metallic pipes supplying services and metallic waste pipes (e.g. water. gas)
(ii) metallic central heating pipes and air conditioning systems
(iii) accessible metallic structural parts of the building (metallic door architraves. window frames and similar parts are not considered to be extraneous-conductive-parts unless they are connected to metallic structural parts of the building).
Supplementary equipotential bonding may be installed outside or inside rooms containing a bath or shower, preferably close to the point of entry of extraneous-conductive-parts into such rooms.
Where the location containing a bath or shower is in a building with a protective equipotential bonding system in accordance with Regulation 411.3.1.2, supplementary equipotential bonding may be omitted where all of the following conditions are met:
(i) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
(ii) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
(iii) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.
NOTE: The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may be assessed. where necessary. by the application of Regulation 415.2.2.

Well that is what the regulations say. It means if you have a RCD 30ma at 40ms on all circuits in the bathroom you don't need to bond. At one point we went OTT with the idea of bonding metal door handles. The idea of bonding is to make all items the same voltage whatever that voltage may be.

The real problem is unless bonded a fault in an immersion heater remote from the bathroom could make pipes in the bathroom live. So all pipes that are metal going between rooms were bonded so any fault would blow the fuse.

The problem is with plastic pipes one can't be sure what is connected to earth and what is not. As electricians we use an earth loop impedance meter the measure the effectiveness of bonding so rather than just connecting wires all over the place we can just connect earth wires where required.

Bonding is not the be all and end all and there are times when to bond can cause a problem. For example if you bond a metal soil pipe it could mean someone outside could touch that pipe and get a belt even though some one inside in the bathroom has a safe environment. Also it could cause holes to be made in the pipe due to electrolysis.

Every house should be inspected and tested every 10 years or on change of owner this is in the main to find where earth has been lost and if you want to be sure things are correct then getting a periodic inspection is the way to go.

It is so easy to quote regulations like the one I have posted and for there to be something which has been overlooked. For example in many houses the bathroom lights are not on a RCD.

So what is RCD protected in your house? And is it a 30ma? For TT systems RCD's have been used for years. But these are 100ma S type RCD's more designed for fire protection then to stop you getting a shock. So you do need to check what is fitted in your house.

We here again and again do a risk assessment. But to do that you need to understand the risks and balance them. And the problem with DIY is people do not understand the risks.

My son on his boat disconnected the earth wire from shore supply. Then used an isolation transformer. This is because other wise it could eat a hole in the boat. I point this out just to show it is not a case of just earthing everything one needs to study the installation and do the appropriate work for that installation it is not a one size fits all.
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