OT: thieving scum (fancy a holiday nige?)

Sounds like an occupational health issue then.

Steve

Do you reckon he should go and see an accident claims lawyer?

This is true but the "wholes house" RCD should be 100mA time delayed device as fault protection if the earth loop impedance is too high to allow large enough fault currents that will trip protection devices in the required times.

The rings should still be protected with 30mA non-delayed RCDs for shock protection. You have the two different types of RCD to provide discrimination, the 30mA non-delayed RCD should trip before whole house one does, thus *not* turning the lights out.

Doesn´t it all depend on the earth loop impedance ?

Steve

I wasn't intending to go into such detail but yes, this is correct for a TT installation. Except that there's no 'if' about it, the impedance of a domestic earth electrode is always too high and you have to allow for it to increase with dry weather, corrosion etc so the RCD is always needed. If memory serves the regs make it compulsory but I haven't got them to hand.

That's true, and in the case of a TT installation all rings must be on a 30mA RCD not just the down stairs one. Greg

It's all _because_ the earth loop impedance is too high with an earth electrode, but there are no choices, you have to fit the RCDs. Greg

It's all _because_ the earth loop impedance is too high with an earth electrode, but there are no choices, you have to fit the RCDs. Greg

This bit seems to cover it:

I note their use of the word 'may' rather than perhaps 'must.' Maybe I'm not fully understanding it.

Julian.

As I daid I don't have the books here so can't check if it's actually mandated. But the reality is that a domestic earth electrode is at best a few tens of ohms and that's not low enough to provide protection against indirect contact with an MCB. Such protection is mandated, so an RCD is always required on a TT installation, i.e. one where the supply does not provide an earth at all. Greg

The question that the above answers is: "Can an RCD be used as a main switch for an electrical installation?" This is asking if an RCD can be used as the main isolation switch instead of a normal main switch.

This is not really related to any requirement to fit a whole installation RCD when the earth loop impedance is too high. What it is saying is that a suitably rated (regards breaking capacity, time delays, trip level etc) can be used as the main switch, provided it is housed in an all insulated enclosure.

AIUI you should measure the loop impedance and make a decision based on that.

A properly constructed local ground system can be superior to a TN scheme, and thats not a single 10mm rod bedded 2 feet down either.

Steve