As far as I can see the earth is simply a cable bonded to the incoming cold
water pipe - just before the main stop tap. There is a copper conductor that
runs from this bonding to a block near the CU. All the earths from ring mains
etc meet there. I can't find any other incoming earth with the supply cable(s)
ie from the elec. suppliers. The house was build in the 50's and has not been
rewired! Is this a TT system?
Most probably the water pipe is the earth! That's how it was done in
the olden days. If it was my house I think it would be time for a
complete rewire. I'm sure there would be plenty more problems you
could find that would certainly condemn it.
Sounds like a non-compliant TT system (it may have been compliant when
installed, I don't know). To fix it, you need to add an earth rod and an
unbroken cable between it and the earth block. Then add a 100mA time delay
RCD to the entire system and ensure that socket circuits and other high risk
circuits are on RCBOs, or the RCD side of a split load consumer unit with
I would also check your main equipotential bonding. It you've got gas or
other metal services, these need to be bonded too. Do any new main
equipotential bonding in the sizes specified for TN-C-S, so that it is an
easy upgrade if it becomes available. Skimping on cable and then doing it
again in five years because the cable is now too small is not a good idea.
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