One of the most frequently asked questions you’ll get asked by an electrician in either a domestic property, is where does the water and gas main come into the house. This isn’t because they want to look through your cupboard and take a sneak peak at your shopping, more so to check the presents of a bonding cable. They will be doing all of the following checks;
- There is a bonding cable there in the 1st place
- That it is of adequate size for the installation
- It’s actually fitted to the pipe itself.
- Continuity from the consumer units earthing terminal/MET to the pipe/structural framework itself to prove functionality
To understand why bonding is so important you must 1st understand what earthing is and how it works.
It’s important to understand the concept of earthing in general. The purpose of it is vitally important. And is designed that in the event of a fault that the quickest route for the fault current is reached. This coupled with a fault protective device such as an RCD enables the RCD to disconnect(trip) within maximum disconnection supply and disconnects the supply from the fault. It is for this every same reason that the cable needs to be of adequate size increase a fault ever did occur.
It is important that under these fault conditions that all of the potentially extraneous conductors are earthed as a difference in touch voltage may occur.
- Example 1 – if there is a fault with the washing machine and you just so happened to touch the outer casing and the kitchen sink at the same time you could come across an electric shock. If the kitchen sink is at 0 volts and the fault current in the washing machine is 100v then you would receive a shock of 100v.
- The 2nd purpose is to stop any potential differences to any metal incoming services (water, gas, structural steel and so on) into your property. It ensures that these services will be at the same potential earthing voltage as the rest of the installation.
– Example 2 – if there was a fault in the road with the electrical supply from the supply board(DNO) that fault current could travel through the earth and into the installation by the exposed conductive part ie the gas pipe. The bonding conductor would then prevent the installation earth and supply earth from having a potential difference.
Remember electricity only works if there is a difference in voltage.