External garage electricity wrongly connected to neighbours supply

[SUNRAY]

Maybe I'm being dim, but could you perhaps explain that statement?

Other than in TN-C-S installations, there is not uncommonly a significant N-E potential difference (due to VD in the supply neutral) - and, indeed, even with TN-C-S there is not uncommonly a significant PD between the CNE/PEN (hence N & E within the installation) and 'true earth' (for the same reason). However, in no case does that result in any 'potential for tripping' of an RCD.

Of course it does.

 

[JohnW2]

Of course it does.

You may regard it as a matter of "of course" but, as I wrote, even if it's because of my being dim, I'd be grateful if you could explain why you believe (if I understand you correctly) that a significant N-E potential difference may result in an increased possibility of RCD tripping. Thanks.

 

[Harry Bloomfield]

You may regard it as a matter of "of course" but, as I wrote, even if it's because of my being dim, I'd be grateful if you could explain why you believe (if I understand you correctly) that a significant N-E potential difference may result in an increased possibility of RCD tripping. Thanks.

My guess as to what is meant.... With a potential between N & E, even when the MCB is off, shorting N to E, can cause the RCD to trip.

 

[JohnW2]

My guess as to what is meant.... With a potential between N & E, even when the MCB is off, shorting N to E, can cause the RCD to trip.

If there are any active loads on any circuits in the installation, an N-E fault (on a final circuit, even if its SP MCB is 'off) will result in an RCD trip even if there is (or was, prior to the fault) no potential difference between N & E, won't it?

That being the case, I therefore can't really even "guess" what situation/mechanism Sunray was thinking of.

 

[ebee]

The developers might well have known, but responded 'so what'. How would the subsequent owners find out - the power would work, the light would work, why would they bother to investigate?

Well that is certainly not impossible with some firms.
I have known quite a few firms (Including some large well known firms too) doing things that are, in my humble opinion, at least slightly or sometimetimes very dishonest, aparently they seem to think that they have the upper hand in size and clout to be opposed by "the common man" , multiple examples of large supermarket firms running roughshod over their employees, tour operators over their customers, insurers over their customers, etc etc.
I will not mention the post office scandal and some recent events either.
It is only when David continues to battle Goliath thant some things come out eventually, even with court cases pending some of them takes it right down to the wire.
Even some small firms "extract the urine" as a way of habit.
We do not live in an ideal world, we do live in the real world.

So yes Harry I certainly agree that the developers might well have known.
But they might not.
They might not have cared one way or the other.

 

[Harry Bloomfield]

If there are any active loads on any circuits in the installation, an N-E fault (on a final circuit, even if its SP MCB is 'off) will result in an RCD trip even if there is (or was, prior to the fault) no potential difference between N & E, won't it?

Yes, except I had in mind - Sunray isolating at the MCB, in order to work on the circuit, accidentally shorting N to E, which would then trip everything on the RCD. Perhaps Sunray could comment about what he had in mind?

 

[ericmark]

I have considered one of the plus points of some (not all) RCBOs is they can switch off the neutral. We are told both neutral and line are considered as live wires, so need to turn off both to isolate, with some earthing systems we can get away switching line only, but we need to know earthing system before we can say if that is OK or not. All my outdoor supplies are either plugged in (mainly so I can use smart adaptors etc) or they come from a dedicated RCBO.

 

[SUNRAY]

Yes, except I had in mind - Sunray isolating at the MCB, in order to work on the circuit, accidentally shorting N to E, which would then trip everything on the RCD.

Exactly that. But with or without a load connected

Perhaps Sunray could comment about what he had in mind?

I certainly didn't expect to be explaining how a RCD works but I'll start here.
Let's put some figures in place and assume our L&N are 1Ω from the sub and somewhere along the line we have a solid 1V betwix N&E, something resembling this:

How much current will flow in the Ammeter?

EDIT: I suppose I'll have to pre-empt the pedancy and say we assume the RCD is set to the on position.

 

[SUNRAY]

How could they manage to test the new installation, without noticing the error? Which means they either didn't bother testing, or chose to ignore the error.

Oh I can imagine exactly how this can happen:
No power in properties, all the dead testing is done (if any).

 

[AndyPRK]

is it 1A? Do I get a lollie?
Until the rcd trips

 

[ericmark]

is it 1A? Do I get a lollie?
Until the rcd trips

So 1 amp for around 20 milliseconds, but would not be able to set the RCD on.