Earthing and Bonding are two of most important factors in determining the safety of the electrical installation in your home.

Earthing:

Earthing commonly refers to the ‘circuit protective conductors (CPC)’ or you may know them as the green and yellow wires that run inside electrical cables alongside the Live and Neutral Conductors. The earth wire should run continuously from a socket outlet light or other electrical outlet to your consumer unit. Without the earth wire the fuses or MCBs in your consumer unit will fail to work correctly, i.e. failing to switch off (‘trip’) when there is a fault. This is why it is important that when work is being carried out on a circuit by an electrician, that they check the integrity and continuity of the earth (CPC) for that circuit, and that any corrective measures are taken if necessary.

Bonding:

There are two types of bonding; i) Main Bonding and ii) Supplementary Bonding.

Main Bonding

Main Bonding is the use of a separate thick (10mm csa) green and yellow copper cable, to connect the Water, Gas and Oil services to the Earth Terminal in or adjacent to your consumer unit. Connections are made on the metal pipes near the point at which they enter your home, i.e. The Main Bonding for the water is normally connected within 1 meter of your Water Stop Tap.

Main Bonding is there to protect you. A fault current will always try to find a path down to earth, literally to the ground. The current will always take the easiest path to ground.

Rogue currents can exist in metal pipework and other areas of conductivity which remain dormant until touched by a person, who then unwittingly acts as the conductor to earth. By effectively creating a circuit, the dormant then current passes through the human body and thus becomes hazardous.

The purpose of Main Bonding (and Supplementary Bonding) is to create a permanent path for any rogue current to flow to earth. By this means, conductive surfaces like metal pipes and kitchen sinks cannot become dormant conductors of stray currents that are waiting to reach earth through the human body.

As long as the water pipe, gas pipe or oil pipe coming into your property are metallic, Main Bonding is compulsory in all circumstances, even when the rest of the pipes in your house are plastic.

Supplementary Bonding

Supplementary Bonding is the use of a smaller, thinner (4mm) green and yellow copper cable to connect together all metal surfaces in a particular area. This area is typically the bathroom, or any other room containing a bath or shower. The 17th Edition Regulations is a little less demanding than the 16th Edition when it comes to Supplementary Bonding. There may be cases when no supplementary bonding is required in the bathroom, i.e. all the pipes are plastic. There could be other circumstances also when no supplementary bonding is required but since the regulations and calculations involved would be impossible to translate into layman’s terms, only an electrician could really come to that judgement.

Other areas where you may find or need Supplementary Bonding.

Area around Central Heating Boiler, Combi Boiler, and Immersion Heaters, where all the metallic pipes should be connected together with a green and yellow cable. Supplementary bonding can be installed in the kitchen, i.e. connecting kitchen sink with the hot and cold water pipes, a lot less frequently these days due to the relaxation in the 17th Edition with regards to Supplementary Bonding. That said, it’s better to be safer than sorry.