Domestic Earth bonding requirements

In each installation main protective bonding conductors shall connect to the main earth terminal. These should connect to 1) water installation pipes 2) gas installation pipes 3) other installation pipework and ducting 4) central heating and air con systems 5) exposed metallic structural parts of the building. In relation to the main earthing conductor - this should no less than half the cross sectional area of the tails.. so for standard 25mm tails you would use 16mm Green/Yellow. Bonding - the recommended for domestic is 10mm, but using the adiabatic equation could allow 6mm but the cost is negligible... stick with 10mm. If the incoming water supply is in metal and then goes off in plastic... I would put a bond in any case if it is easy to... It is still an extraneous metal conductive part and connected to earth - not worth the hassle later, as could be altered in years to come. If it going to be a huge hassle and a big cost then this could be left, provided RCD's are provided for every circuit. If there is any metal work further down the line and without RCD protection on some circuits then I would install a supplementary bond where appropriate of 4mm If the incoming supply is in plastic, then obviously there is not a good connection to earth from the incoming pipe, but if there is a great deal of metal work around after that point - for example the heating system - and you do not have RCD protection, bond any relevant water metal work. A supplementary bond may do of 4mm if using green/yellow singles if the metal work is in an airing cupboard. If the install is all in plastic with copper rising just for show, no need to bond.

Most households will need 16mm bonding into the fuse board and 10mm to the water and gas. The earth cable is green and yellow. I always try to get an earth bond to gas and water unless they are entirely in plastic. We recommend the fuse board has one or more RCDs to cover the whole of the electrical installation. If this is not the case then supplementary bonding is required in 4mm cable. Sometimes difficult to achieve and unsightly.