Joining two earths?

[george [dicegeorge]]

I have 2 earth spikes about a yard from each other, one connected to the ancient house wiring, one connected to a new Consumer Unit which runs three sockets in corners of the house, I had it installed when I moved in 3 years ago to power electric heaters etc as I didnt trust the old wiring.

Can I join the earths from the 2 spikes together?

I had thought that the electrician did it like that so as not to trip his RCDs, or something like that, but lately I'm coming to believe that he did it for legal reasons, so that he wouldnt be held responsible for the ancient wiring.

I believe there would be less resistance in paths to earth if I join the two earth circuits together, so that is a good idea.

Am I right? Or is there more to it?

[g]

[Bob Minchin]

The point about linked wiring causing RCD tripping can/will occur when the neutrals are linked between different circuits. I cannot see a situation where bonding two earths together will cause an RCD trip. Like you, I think it can only lead to a lower impedance earth but not necessarily a significant improvement. Your spark may have made a measurement of the earth impedance on the old wiring and found that it did not meet current regs and therefore he could not use it. Provided that your old earth met regs when it was installed, it still meets regulatory needs. Bob

[Tabby]

Do you have an ELCB, RCD or no more earth leakage protection than fuses on the old wiring?

NT

[dave]

It would be impossible afaik to -increase- the Z(E) by joining two (or more earth electrodes directly. According to Mr Ohm anyway. Unless of course one of them was generating a potential :-)

[Chris Hogg]

When I had a new consumer unit installed, the electrician found just what you describe. He put an additional spike in, some distance from the first, which brought the impedance down to acceptable levels, so we now have two earth spikes both coming from the one CU.

[george [dicegeorge]]

The old fuseboxes hae one RCD inserted before them, the new consumer unit alsohas an RCD.

So I think it would improve things to connect the two earths .

[g]

[Tabby]

A modern RCD on each at least means that connecting them wont export TT related dangers from the old circuit to the new.

Its only going to improve things if your earth impedance is too high for some reason.

NT