Tripping rcd

[NeonSparks]

just moved an mcb to rcd side of board and now a lighting radial on NON rcd side trips rcd...any ideas? I'lm sure i have moved correct wires.

 

[olly w]

Sounds like a borrowed neutral.
What circuit was on the mcb that you moved?

 

[Sintra]

Have you moved the neutrals onto the correct bars in the cu or else it could be a borrowed neutral between the circuit you moved and the lighting circuit.

 

[NeonSparks]

it was the upstaire lights(fitted downlights to bathroom) .....the downstairs lights trips

 

[Sintra]

Borrowed neutral between the 2 lighting circuits.

 

[NeonSparks]

so a neutral from downstairs joins with N from upstairs you think?

 

[NeonSparks]

so the only way to sort it is to find link and (cut it)?

 

[olly w]

I would guess that the neutral as been borrowed for the two way switching for the landing.

 

[Sintra]

Absolutely the landing light is probably on the downstairs lighting circuit due to the 2 way switching but the neutral will be taken from the upstairs circuit.

 

[bugsy]

Yes, line from ground floor 2 way feeding landing light and return on 1st floor lighting circuit

 

[NeonSparks]

ah ok. that gives me something to go on......thanks for all the quick replys!

 

[NeonSparks]

would that make it trip on its own or could there be an earth fault on that radial?

 

[bugsy]

If its a borrowed neutral thats the problem and if as you have said it only started after you repositioned the mcb seems crystal!

 

[shirlock]

Can't you put both lighting circuits on rcd side and note on cu about borrowed neutral if customer doesn't want to pay for fault finding?

 

[NeonSparks]

lol ok cool...thanks for replys

 

[bugsy]

out of curiosity why did you move the mcb

 

[NeonSparks]

because a bathroom radial has to be on an rcd?

 

[Hawk81]

Can't you put both lighting circuits on rcd side and note on cu about borrowed neutral if customer doesn't want to pay for fault finding?

surely you cant leave a borrowed neutral. either find the borrowed neutral and fix or put both lighting circuits onto the 1 mcb.

 

[Marvo]

If two circuits are sharing a neutral you can move both the circuits to the RCD side of the board along with their neutral(s) and peace and harmony should be restored.

 

[Hawk81]

If two circuits are sharing a neutral you can move both the circuits to the RCD side of the board along with their neutral(s) and peace and harmony should be restored.

i would not say peace and harmony are restored by leaving a borrowed neutral as this is dangerous. surely not great advice!!

 

[Sintra]

Agree both would have to be on same mcb as you have stated.

 

[Ponty Massive]

Agree both would have to be on same mcb as you have stated.

Why's this? If both circuits share the same neutral, by putting both MCB's on the same neutral bar (and same RCD) then surely it's the same thing?

To have upstairs on 1 mcb and downstairs on a different MCB (albiet on the same RCD), would that not be better than powering 2 circuits through the same MCB?

 

[Sintra]

No because if one mcb is isolated to work on a fitting then the borrowed neutral will become live if the other circuit is not also disconnected.

 

[Hawk81]

Why's this? If both circuits share the same neutral, by putting both MCB's on the same neutral bar (and same RCD) then surely it's the same thing?

To have upstairs on 1 mcb and downstairs on a different MCB (albiet on the same RCD), would that not be better than powering 2 circuits through the same MCB?

As i have already stated in an early post the reason for puting the "2" circuits on the one mcb is because a borrowed neutral is dangerous. If there is a borrowed neutral then the are not truely 2 separate circuits.

 

[Ponty Massive]

No because if one mcb is isolated to work on a fitting then the borrowed neutral will become live if the other circuit is not also disconnected.

I know your right, but I can't get it straight in my head.

Lets say there was no borrowed neutral and both circuits wired correctly, both MCB's connected to the same RCD and same neutral bar, are the neutrals still not connected together, only this time at the board rather than at the light fitting?

 

[Sintra]

Yes connected together at the cu is not a problem and is in no way the same as a borrowed neutral.

 

[Hawk81]

I know your right, but I can't get it straight in my head.

Lets say there was no borrowed neutral and both circuits wired correctly, both MCB's connected to the same RCD and same neutral bar, are the neutrals still not connected together, only this time at the board rather than at the light fitting?

The difference there is that if you isolate one circuit to work on it and the other circuit is still on the circuit that is still on has a neutral connected to the board and therefore a return path for te current. In the case of a borrowed neutral when you split the circuit at the borrowed neutral you are breaking the return path to the board therefore that neutral will be live.

 

[Sintra]

Well said Hawk couldn't get it into words myself, the beer has taken over.

 

[Hawk81]

Well said Hawk couldn't get it into words myself, the beer has taken over.

Lucky you, no beer for me tonight up early for work in the morning! but i will make up for it tomorrow night lol

 

[Ponty Massive]

The difference there is that if you isolate one circuit to work on it and the other circuit is still on the circuit that is still on has a neutral connected to the board and therefore a return path for te current. In the case of a borrowed neutral when you split the circuit at the borrowed neutral you are breaking the return path to the board therefore that neutral will be live.

Thank you, that's a very good explanation. I do understand what your saying, but I'm struggling to picture it in my mind...must be getting tired

 

[Sintra]

Start at 8 in the morning too. Can't wait.

 

[Ponty Massive]

I'm in for 7, and need my beauty sleep........night all!!

 

[Sintra]

Good night mate..........

 

[Marvo]

i would not say peace and harmony are restored by leaving a borrowed neutral as this is dangerous. surely not great advice!!

Sorry it wasn't meant to be taken as good advice, hence the smile. I'll wrap it in [Sarcastic][/SARCASTIC]tags next time.

 

[telectrix]

think it could be put more simply. all are talking of a borrowed neutral, but i would rather call it a borrowed live. the landing light is upstairs, so is on the upstairs lighting, but only as as regards the neutral, but has " borrowed " the live from downstairs. therefore, if you isolate the upstairs, you still have a live from downstairs to the landing light.

 

[Ponty Massive]

think it could be put more simply. all are talking of a borrowed neutral, but i would rather call it a borrowed live. the landing light is upstairs, so is on the upstairs lighting, but only as as regards the neutral, but has " borrowed " the live from downstairs. therefore, if you isolate the upstairs, you still have a live from downstairs to the landing light.

That's a better way of looking at it!