DIY Doctor

Unearthed lighting circuit and bathroom light

Postby mat_12345 » Thu Sep 03, 2020 3:48 pm

So...long story short..

1970s house. Twin and earth grey cabling. Moved in earlier in the year and replaced the original fuseboard with a modern consumer unit. Both electricians that quoted for the job seemed confident that a full rewire wouldn't be necessary.

After the job was done, something kept tripping the RCD. The eletrican thought it was due to an earth fault on one of the lighting circuits and so he had the earths on the upstairs and downstairs lighting disconnected at the board.

I was reasonably reassured this would be ok as all the switched are plastic and the light fittings are plastic pendants.

Now I'm looking at getting the bathroom re-done. Is it as simple as getting a class 2 light in there?

Is it daft to carry on without an earth? We are just trying to avoid rewire disruption if possible.
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Postby Mr White » Thu Sep 03, 2020 6:21 pm

Just because it works does not mean it is safe, the earth wire is there to provide protection for the cable as well as the fittings.

You need a different electrician, and yes, some if not all of it will probably need rewiring. A decent electrician would have tested everything before changing the consumers unit, that way they would have found any potential errors and could have taken care of it at the time.
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Postby ericmark » Thu Sep 03, 2020 7:43 pm

I would say bring back hung draw and quartering for electricians doing that. It was banned back in 1966.

However some thing similar with dads old house, what one should do before fitting a RCD is to check the leakage, for a 30 mA RCD with no faults the limit is 9 mA, there is always some leakage with any AC supply, induction and capacitive links means there is always a little leakage, even when the insulation resistance is infinity using a 500 volt tester, although we are not allowed to put down infinity, once using an AC current likely some leakage.

So before the electrician starts he should test each circuit, if he can combine 3 or 4 circuits onto one RCD without exceeding the limit then using one RCD for a number of circuits is allowed, however if due to premises size he can't get the readings required he may need to use RCBO's which is a MCB and RCD combined, so by having in my case 14 RCD's the leakage on each is reduced.

The daft twit who did my dad's house simply did not have any test gear, at that time RCD protection was not required, so he swapped it for an isolator, but basic problem was 1954 wiring, and once dad died I got the house rewired.

What he has done is extremely dangerous, with a know fault no way should the earth be disconnected, lights should be turned off at the consumer unit until the fault is found.
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