Old bathroom earthing?

26 Nov 2007
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United Kingdom

I have brushed on this point before but some investigation has revealed something with which I could do with some more advice.

Next week I have an electrician coming in to fit a CU.

I have been examining the existing bathroom bonding in my house and have identified that there is a 4mm earth cable running from my MET to one pipe feeding a bath tap. There was then a 4mm that appears to have previously linked the two bath taps but has been removed from one pipe by a previous owner.

Please advise if (as stated in previous questions) I should run 4mm from bathroom radiator, to bath taps and basin taps and then connected to the lighting earth?

Is there any requiredment for the existing 4mm cable that runs from one bath tap to the MET?
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There is no requirement to join the bonding to the MET, basically all you are required to do is create the same potential on all the devices so no current can flow between them if you touch two of them. Why don't you consult this electrician "coming round"?
In summary, you have to connect the CPC (earth wire) of every circuit that enters the bathroom, with every metallic service that enters the bathroom.

That means the lighting circuit, the Immersion heater (if any), the Central Heating pump (if it's in the bathroom), the shaver point (if it's not on the lighting circuit; the electric shower (if any), the shower pump (if any). All joined to the hot water pipe; the cold water pipe; the cast iron or lead waste or soil pipes (if any); the radiator pipes (flow and return).

You only need to join to each circuit once, and to each pipe once. So you haven't got e.g. to join to each of six lamps, and to the cold water pipe at the bath, the shower, the bidet, the WC cistern. Join to the services at their point of entry to the bathroom, or immediately outside (e.g. in an adjacent airing cupboard) if more convenient. If you bond to the copper pipe at its point of entry, it doesn't matter if it subsequently changes to plastic pipe - since there is no metal in the bathroom that can introduce a potential from outside, since you have bonded it all at point of entry. Obviously you won't be dragging an electric fire in there on an extension lead :rolleyes: You can use an Earthing Block to gather together all the wires. It is slightly better to run a single wire from clamp to clamp rather than having separate cut lengths, in case one comes loose or is snagged. the camps must be visible for testing and maintenance (so not hidden under the floor or tiled over). You can often connect to the lighting and shower circuits in the ceiling switches. This is not notifiable work, it is an easy DIY job.


(if you look at the top of the Electrics UK Forum you will see "Please see if the answer to your query is already covered by the Wiki"

Just click on it for lots of common stuff like this)

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