Help please with understanding a borrowed neutral

[baza]

Hello everyone
Could someone explain why the following happens with a borrowed neutral?
Did a cu change today and installed a dual rcd board, Previously the up and downstairs lights were on the same mcb. I was half expecting the rcd/s to trip when I separated them, which they did. I dont need help in how to remedy this, but my question is when disconnecting the link at the back of the switch feeding the strappers linked to the other switch, I would have thought that I had removed the inbalance and the rcd would remain on.
Thanks in advance

 

[hasel5]

You a 5www?

 

[telectrix]

in this situation, it's not what i call a borrowed neutral more like a borrowed live, where the L for the landing light comes off the downstairs. by removing the L link, you will lose the landing light, but it should sort the RCDs out, as they only trip when you switch the landing light on. time to do some testing. bet you have a neutral in the wrong bar somewhere.

 

[onions1066]

You a 5www?

Not really helpful reply

 

[derek]

Try drawing a circuit diagram of the scenario you are looking at, it might help to explain it.

 

[Scornio]

Hi Baza,

try putting the two lighting circuits back on same rcd... If it holds in them seems you still have a borrowed neutral.

 

[baza]

Hi Scornio
yes they do hold when I do that. My misunderstanding is by disconnecting the link from down to upstairs I would have thought the imbalance would have been removed or am I thinking wrong

 

[ste77]

Hi Scornio
yes they do hold when I do that. My misunderstanding is by disconnecting the link from down to upstairs I would have thought the imbalance would have been removed or am I thinking wrong

see post 3

 

[Scornio]

Hi Baza,

Your not thinking wrong, I'm just implying that you still have a fault and seems likely to be a borrowed neutral. I would look again closer.

 

[telectrix]

if you have dissed the L from downstairs and it still trips, then, as you say if the lights are on the same RCD and it doesn't, that suggests the problem is still with the lights. could be a DIY job for an outside light where, unable to get a N at a switch, some numpty has borrowed it from the other lighting circuit.

 

[guest119]

Are you actually taking money from people for electrical work?
Not a ribbing by the way, a serious question.
Boydy

 

[baza]

Thanks Telectrix, spot on, I rewired the borrowed live and put a neutral in the right bar, I feel daft missing that one.

 

[Silly Sausage]

Try drawing a circuit diagram of the scenario you are looking at, it might help to explain it.

Sound advice!

Amazing how it clarifies a problem sometimes.

 

[lofty84]

Im not a Electrical Trainee but dont really understand this borrowed neautral business. Its not a good look but can anyone explain to me what is occuring in this instance and maybee give me an example of it, and maybee even how you would put it right.

fingers crossed I dont take to much of a kicking for asking ...

 

[trev]

In a nutshell it's where someone joins the neutral from one circuit onto the neutral of another, often because of laziness or not having a bloody clue