More about main equipotential bonding
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Dadwood
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More about main equipotential bonding

by Dadwood » Sun Apr 12, 2009 9:58 pm

The recent topic about eqipotential bonding got me tracing the wiring in my own home and raises a question. My MEB cables are two in number; each being 4 mm CSA. One connects the MET to the incoming steel gas pipe at a point alongside the meter. The other connects the MET to the incoming water pipe immediately next to the stopcock. It's properly clipped to the 15mm copper pipe, but the actual incoming pipe before the stopcock is heavy black plastic, so there's no chance of earthing by that route. I would rest easy if someone could just confirm that such an arrangement is in order.

kbrownie
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by kbrownie » Mon Apr 13, 2009 11:48 am

Dadwood,
In a lot of cases the supply services such as gas and water main feed to properties are plastic.
So this is not uncommon.
Your system should be earthed via your incoming electric supply(TN) or an earth rod/electrode(TT).
The MEB raises the potential under fault condition to as close to zero as possible within the equipotential zone which is your house not outside it, and will find a path via the MET Connection and Earth Bonding to earth.
So nothing to worry about but you MEB cables should be at least 6mm if TT arrangement or 10mm if TN arrangement.
Hope this answers your question.
KB

Dadwood
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by Dadwood » Mon Apr 13, 2009 3:25 pm

Hi kbrownie,
Many thanks for your reply. My system is indeed earthed via the incoming supply. I made an error; the two MEB cables are both 10mm CSA.

Dadwood
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by Dadwood » Tue Apr 14, 2009 8:22 pm

Hi again kbrownie,
After reading your recent helpful reply, I got to thinking a bit more about the earthing of my water pipework that I mentioned earlier. The pipe is earthed alongside the stopcock, and takes a supply to the kitchen cold tap. It also runs up to supply the storage tank in the loft. But that tank is plastic, so as far as I can see the copper pipes coming OUT of the tank are not earthed. Ought I put an earth wire between the incoming copper pipe and those leading away from the tank?

kbrownie
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by kbrownie » Wed Apr 15, 2009 12:35 pm

you can do that

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