Another borrowed neutral question

Help Support Talk Electrician Forum:

norv

Senior Member
Joined
Feb 16, 2008
Messages
126
Reaction score
0
Going back to a job on Thurs.

Changed the CU & the RCD trips when the socket CB is turned on. I've got my trusty fault finding list ready, but just to confirm if there was a borrowed neutral from a lighting circuit to sockets or vice versa then wouldnt the RCD trip only when one of the lights were switched on or something was plugged in? I'm 99% sure everything was unplugged & all lights off when I did the CU change

 

steptoe

of course Im wrong, ask my wife™
Joined
Feb 13, 2008
Messages
24,422
Reaction score
160
Location
Gtr Manchester
have you done an IR test?

that would prove a lot of yes/no/maybes.

do it across the whole board first, then if its dodgy start taking one cable out at a time, use either all P or N or E depending on the fault. dont mix them.

if you think its a borrowed N from wrong side of board then turn RCD off and switch something on other side of board on, should give you 230v potential on your RCD Neutral bar.

 

The Godfather

Retired
Joined
Mar 24, 2008
Messages
1,302
Reaction score
0
Going back to a job on Thurs.Changed the CU & the RCD trips when the socket CB is turned on. I've got my trusty fault finding list ready, but just to confirm if there was a borrowed neutral from a lighting circuit to sockets or vice versa then wouldnt the RCD trip only when one of the lights were switched on or something was plugged in? I'm 99% sure everything was unplugged & all lights off when I did the CU change
Isolate all sockets (unplug everything), does the RCD test perform OK?

If not (trips, regardless), then check the Neutral bars/wiring in the newly fitted CU.

And check you haven't crossed a neutral.

If no joy, then disconnect (isolate completely) circuits one by one until fault disappears.

Hope this helps.

Don

 

norv

Senior Member
Joined
Feb 16, 2008
Messages
126
Reaction score
0
Ok thanks. I know I should have done more tests before ripping out the old CU but that day was not my day. X(

Had a fault like this before & it was a neutral touching a back box.

Unfortunatley the customer isnt too helpful & doesnt want me there until 10.00 so need to get there with a clear head & some good fault finding tactics

 

SPECIAL LOCATION

Trailer Boy - Electrician.
Joined
Mar 28, 2008
Messages
13,633
Reaction score
317
Ditto steptoes point need to verify IR test reading on suspect circuit..

before assuming borrowed neutral...

When all basics have been proved then start checking for the more obscure.

Is it a downstairs or upstairs socket circuit??

Borrowed neutral on sockets is a far more rare bird than on lighting circuits..

But I have had the occasional one such as..

Downstairs light circuit joined to Upstairs sockets... when DIY bob can't find a neutral on the light circuit and he is adding a new light somewhere, so he joins it onto the nearest socket j/box under the floor.

More common things to RCD trip socket circuits may be...

duff appliance plugged in somewhere..

fridges/freezers with dodgey pump motors..

electric kettles with the cordless plug-in base arrangement, and the base has damp in it!

unsheathed earth wire touching a neutral in a socket/spur/Jbox...

table lamp with wires crossed in the 13a plug top.

Keep your investigations simple to start off with:)

?:| ? :|

 

steptoe

of course Im wrong, ask my wife™
Joined
Feb 13, 2008
Messages
24,422
Reaction score
160
Location
Gtr Manchester
oh, just a thought, (on reading SL's post)

have you moved a washing machine or similar?

had this once, kept tripping out for about a day...

turned out (after Id been talking to a few people) that sometimes water can splash up round the workings and cause damp where it shouldnt be, tripping out everything in sight.!!!

next day everything was fine. damp just evaporated, or something.! :|

oh yea, and the table lamp thing, have seen that loadsa times, N wired to the Earth pin, god alone knows why..... :eek:

 

SPECIAL LOCATION

Trailer Boy - Electrician.
Joined
Mar 28, 2008
Messages
13,633
Reaction score
317
oh yea, and the table lamp thing, have seen that loadsa times, N wired to the Earth pin, god alone knows why..... :eek:
there is that phone call just after dusk...

on the day you have swapped out the CU...

Customer: "hello that you board you fitted is faulty"

Electrician: "whats the problem?"

Customer: "all the powers gone off"

Electrician: "what ALL of the power? lights as well"

Customer: "er no.... just the sockets"

Electrician: "what did you do last.. have you plugged somthing in?"

Customer: "no... no... nothing at all"

Electrician: "so what were you doing when the power went?"

Customer: "nothing I just sat down to read the newspaper, and put on my reading lamp by the chair!"

Electrician: "Go and turn your reading lamp OFF, then reset the switch on the fuse board check that the power stays on..."

Customer: "Yes powers back on now!"

Electrician: "OK try switching your lamp back on again... if the power goes off again then your lamp is faulty so don't use it till its repaired..."

2mins silence...

Customer: "well I just dont understand that..... It worked alright on the old board????"

Electrician: "Doh!!!!X(X(X("

:^O :^O:^O:^O

 

norv

Senior Member
Joined
Feb 16, 2008
Messages
126
Reaction score
0
Thanks for the pointers:)

This is a 6 bed house (basically a 4 bed detached with a 2 bed annexe built on the side) The annexe side of it is working ok. The rest of the house has 1 ring but when I turn off the ring the kitchen lights go out so the fault maybe pointing me in this direction.

I was only adding a cooker circuit to start off with & then they decided they wanted a new CU.

Customer: "well I just dont understand that..... It worked alright on the old board????"
I've almost given up trying to explain. Some handouts might be a good idea to give to customers so they can read them at bedtime

Well.... You know I said the customer isnt very helpful, I had a call today to cancel Thurs & they will ring me when they want me to come back. I explained that there was a problem that need sorting but because the power is on they dont seem bothered.

 

SPECIAL LOCATION

Trailer Boy - Electrician.
Joined
Mar 28, 2008
Messages
13,633
Reaction score
317
Well.... You know I said the customer isnt very helpful, I had a call today to cancel Thurs & they will ring me when they want me to come back. I explained that there was a problem that need sorting but because the power is on they dont seem bothered.
Ah the age old problem...

The customer is always right.... :(

even when they are wrong!! :_| :_|

 
Top