My mother has just had a new gas meter fitted in her house and the engineer gave her a Safety Notice saying ' It appears that the gas installation pipework fitted at your property may not have Electrical Equipotential Bonding correctly fitted. I am required under section 18(2) of the Gas Safety (installation and Use) Regulations 1998 to advise you that the Electrical Installation should be checked by the local electricity company or by a competent electrical contractor'.
What should she do? This will have been in this state for years now. Does is cause a safety problem? What is Electrical Equipotential Bonding?
That in itself is not particularly serious and would be easily fixed, but it may be an indication of more serious deficiencies in the wiring. Ideally, your mum should get a recommendation of a local electrician from a friend or neighbour who can inspect the installation and advise. Do you know the history of the wiring installation, e.g. how old, how well maintained, when last inspected (if ever)?
The house was renovated around 30 years ago. There has been no trouble with the electrics since then. I would assume that all necessary earthing has been carried out at that time. No further work has been done to the house. It is an ex-council house so any electrical deficiencies would have been dealt with by the council. This is the first time that anyone has indicated a possible safety hazard. I know that this maybe a reaction to increased safety specifications and suspect that is what this is. I might just get her to have an electrician take a look.
To get an electric shock you need a voltage difference. Electricity tries to go to earth and it will do so by the easiest route. Lets say for argument's sake your cooker develops a fault and the metal work becomes live, which can happen if there is a wiring or earthing defect. If you then touch the cooker and say a metal draining board, or anything else with a connection down to earth, the current will flow through you to get to the draining board to get to earth, and more current will flow than if you just touch the cooker and nothing else. (Either way you get a shock, just that one is worse than the other). However if you electrically bond together all the metal work in the kitchen, bathroom etc, and the same fault condition arises, all the voltages remain the same (equipotential), there is no volt drop across any of the various bits of metal work and hence a reduced chance of serious shock. Just bear in mind that if you have the fault as described above, and you touch the live cooker case and the draining board at the same time, the current will flow up one arm, across the chest and down the other arm to get to earth. Your heart is between your arms, and it only takes a few milliamps to risk stopping the heart.
If you don't have the bonding there is no need to panic. People have survived since electricity was discovered without it. If the wiring and earthing is OK, and appliances CORRECTLY fused, the fuse will blow and cut the supply anyway. The bonding is just an added layer of protection in case the fuse doesn't blow.
That is as I understand it. I may not have described it well, I am not a teacher!!
Actually the fusing and the equipotetial bonding are a bit more seperate than that:
As previously described the equipotential bonding is there to protect the person should a earth fault develop in an installation. Typically in bathrooms this is also there to protect against having different earth voltages on different circuits.
The fuse is there to protect the installation. It only requires 40Vac at
40mA for 30ms to cause the heart to fail. A standard ring main fuse is
32Amps. The cable is rated above this and the fuse stops the installation and its cabling heating up and causing a fire.
An RCD is there for the protection of the person which hopefully will disconnect at around 30ms in the case of an earth fault.
The problem arise when properties have had installations done over the years, different levels of safety have been introduced at different times and this leads to confusion on what the requirements actually are.
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