SR wrote:

Hi everbody. I've a couple of issuesregarding my home electrics. The
mains supply is via overhead cable, and so is presumably a TT system.
There is a 63A, 100ma RCCD covering the whole installation, but the
consumer unit is a fuse wire type. There is a additional 30ma RCD
protected circuit which supplies an outside shed/workshop via a 6mm
overhead T&E cable.

First issue is the earthing - as far as I can see the only local
earthing is via a spike connected to the earth by the shed. Since this
is via the T&E cable earth wire, which I measure as about 1mm2, this
looks a little inadequate - my understanding that the earth in a TT
system should be 16mm?

Your earth rod will have far higher resistance than the 1mm wire. You
have an RCD to deal with this limitation of TT systems. 1mm is small,
but wiring a high impedance earth with 16mm would be pretty pointless.
On a new install it would not be done the way yours is, but in the
grand scheme of real life problems I'm not sure it really features in
the top 1000.


I'm very happy to install a new earth
cable/spikes if necessary myself, but presumably this is not really
possible under the new regs?

Secondly, I need to arrange an additional external supply for sewage
treatment plant. About 80W. The simplest way to do this would be via an
RCD protected spur off the downstairs ring. Is this OK,

would work fine.


NT