Earth bonding

4 Jan 2006
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United Kingdom
I need some advice on earth bonding before I have a PIR done. My central heating is earth bonded to the fuse box but there is no bonding on the water pipes in the kitchen/bathroom or on the gas pipes. The central heating boiler is next to the bathroom so is it ok to supplementary bond the water pipes in the bathroom to the central heating bonding. An electrician told me you can connect to the nearest electric socket if its too difficult to get back to the fuse box, so in the kitchen there is a double socket thats not far from the water pipes, if not there is a radiator thats not too far away is it ok to use that instead. Lastly what size earth wire should I be using. I think I read somewhere that the supplementary bonding should be half the size of the main bonding so if the main is 10mm the supplementary should be approximately 6mm, is that correct.
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The main incomming water and gas and any central heating pipes that leave the house should be main bonded within 600mm of point of entry to the house on your side of any meters

This is from the main earthing terminal, not via any sockets, etc, and a rule of thumb for TNS is not less than half the size of the main earthing conductor (thats the wire that comes from the service head to the MET, and if the MET is separate from the CU earth bar, links the CU to the MET as well)

If TNC-S then different things apply, but to take account of all possible supply types and fuse ratings, 16 is used for main earth, and 10 for main bonding, that will cover for any supply the house has (unless the DNO has special requirements)

Supp bonding in bathrooms, is in 4 if not mechanically protected, and links together all ECPs and the CPC of circuits supplying equipment (class 1 or 2) in the bathroom zones
You do not need to supplementary bond in a kitchen (this was requird under old regulations). No need to remove it if already present.

In a bathroom 4mm is correct (unless the cables is mechanically protected, which it never is)

The bathroom bonding is to the earth conductor of each circuit which enters the bathroom. This is usually the lighting circuit so try to connect at the light switch or lamp fitting and drop down somwhere inconspicuous. e.g. in the airing cupboard or pipe duct.

If there is an immersion heater, electric shower, shower pump, space heater or any other circuit in the bathroom, bond to the earth terminal on that too. You only need to bond to each circuit once. You can often do a lot of the pipe bonding under the bath, provided you have copper pipes with soldered joints as this forms a permanent joint.

Connections must be accessible for maintenance and have warning labels (these are generally supplied with the pipe clamps).

You can bond to copper pipes just outside the bathroom if you like (e.g. water pipes or radiator pipes that pas through the wall.
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