DIY Doctor

What to do With old Earth Wires?

Postby Browne » Fri Aug 30, 2019 1:21 pm

Hello,

Two questions - both about earthing wires.

I'm renovating my mid-70s house, and see old earthing wires connected to bloody everything - taps, radiators, an extra one to light fittings. I'm told that these are no longer necessary, and the house only needs to be earthed in one place nowadays (mine is where my stop cock and water meter are).

1, As I replace a sink and taps, for example, is it safe/legal to tape up exposed wire and just leave them in walls etc? I'm guessing the 2 ends of the wire will be connected elsewhere.

2, I've seen an additional earth on the bathroom light wiring. So that's a live, neutral, and 2 earths. I'm going from one light to 4 down lights, so can I tape and leave the extra earth, connect it to the first light in the circuit, or do I need to follow it to each of the 4 lights?

Grateful of any help.
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Postby Mr White » Fri Aug 30, 2019 6:27 pm

If you have had a new consumers unit installed with Duel RCD's then some earth wires are considered "redundant" but if you still have your original consumers unit, they have to stay.
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Postby ericmark » Sat Aug 31, 2019 12:43 am

The 17th Edition of the wiring regulations relaxed the requirements on earth wires, as long as every thing else complied with 17th Edition, so near enough every thing RCD protected.

The idea is the RCD will trip with an earth fault, with just 30 mA flowing and if you have earth wires the current which flows could do you more harm, so when assessing the risks, it was decided there was less risk without them than with them.

Not sure I fully agree, but you don't need to bond things in the same way as before, at one point even metal doors and windows were bonded, however before 1966 often there was no earth to lights, today an earth wire must go to lights, even if the light its self is class II and does not need an earth.

The testing today is far more important than it use to be, with a fuse it was designed to blow from memory in 0.1 of a second with a short circuit, with a MCB it will disconnect in 0.01 of a second, however if enough current can't flow with a fuse that time may increase to 0.2 of a second, but with a MCB if not enough current flows instead of the magnetic part working the thermal works instead, so disconnection time can easy jump from 0.01 second to 5 seconds. So testing the loop impedance becomes very important.

Many things have happened over the years, including water mains being replaced with plastic, which with some houses has resulted in there being no earth.

So it is recommended (except Scotland where there are stricter laws) that a house is tested every 10 years or change of occupier. If wired pre 1966 it should tell you.
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