2 way light connected to 2 different circuits

[charlie34]

Hi

I have just carried out a CU change and when I tried to replace the lamp in the fitting on the landing It keeps throwing the breaker. The fitting is 2 way and connected to both the upstairs and downstairs circuit. I haven't come across this method before, so it confused me a bit. How dies this method work and is that the reason for it throwing the trip, or does it sound like another problem.

thanks dan

 

[robd]

Sounds like it could be a borrowed neutral, i.e. switch live from downstairs switch and a neutral 'borrowed' from upstairs lights

 

[Des 56]

Search this forum for threads on borrowed neutral
http://www.electriciansforums.net/e...ripping-lighting-when-switch-2-way-light.html

 

[Brendan976]

Hi
Years ago some sparks would borrow the nuetral from the upstairs lighting circuit to save them running up another cable, its not something i ever did. The only time it really shows up is when you put in a consumer unit with RCD,s and then the imbalance shows up and hence it will trip out. Two ways around it run another neutral, or join both circuits on the same
mcb not ideal but it will work. then note it on the certificate ,I mark up the circuit diagram/schedule to that effect

regards

Ben

 

[robd]

You don't need to put both circuits in the same MCB, just on the same side of the board ie both fed from the same RCD. That is assuming of course that you are using a split load board and not RCBO's?

 

[Des 56]

If there is a borrowed neutral,either reconfigure the wiring or feed them from one mcb

If they are fed by seperate mcbs.there is possibility that
A live can appear via the 2 way at a disconnected neutral, when one of the lights in say the bedroom is being changed

 

[Octopus]

But remember its best to keep the lighting on seperate RCD's (where feasible) so your client doesn't loose their sockets and lights in the same part of the house if one RCD trips.

 

[robd]

Fair point Des...

 

[Knobhead]

I suppose it will all come down to will the customer pay or want the upheaval of the remedial work. A single MCB for all the lighting is probably the way you’ll have to go.

 

[charlie34]

Thanks for all the replies. Yeah it is a split load board and I have tried to keep sockets and lights seperate so, dont lose everything. I think it will be a case of using the same mcb.

Typical really as I'm using this job as one of niceic assesments.

cheers

 

[needasparks]

You don't need to put both circuits in the same MCB, just on the same side of the board ie both fed from the same RCD. That is assuming of course that you are using a split load board and not RCBO's?

Don't worry fella, don't think anyone noticed. when they do, put your head down.

 

[robd]

ha ha noticed what

 

[Knobhead]

Damn, missed that :biker:

 

[ample current]

I had something similar to this the other week, son in law changing the light switches, didnt note how it was wired, and couldint wire the 2 two way lights for the landing and hallway, took me some head scratching also, the live for the landing light was taken from the dining room light switch (which was directly on the other side of the wall in the hallway) and the live for the hallway was form the upstairs lights (only 1 lighting circuit throughout the house)