Lighting circuit tripping RCD

[Litttle Shonet]

Just carried out CU change in a property, and put downstairs lights on one side and upstairs lights on other.

Upstairs lights tripped all the time, so put it on same RCD as downstairs. Now ok.

Is there a crossover of neutrals somewhere in the circuit, and if so whats the best plan of attack

Cheers

LS

 

[M107]

Two way switch between downstairs & upstairs.........will be the landing light.

Rewire the light so it is fed from one circuit.......

 

[Litttle Shonet]

Thanks for that. Will have a look when I go back.

Cheers

 

[SPECIAL LOCATION]

Just carried out CU change in a property, and put downstairs lights on one side and upstairs lights on other. Upstairs lights tripped all the time, so put it on same RCD as downstairs. Now ok.

Is there a crossover of neutrals somewhere in the circuit, and if so whats the best plan of attack

Cheers

LS

It is not a cross-over of neutrals..

It is one (or more) light fittings bridging two circuits..

i.e. Live from circuit 'A' through a light fitting then onto neutral of circuit 'B'

As M107 says 99% chance this will either be landing or hall light fitting dependent upon which way the original sparks joined his two-way switch..

Most often it IS the downstairs live via Hall & Landing switches to landing light then the upstairs neutral..

BUT..

double check before you go diving in..

I have on occasions had the upstairs live coming to the downstairs neutral.

You are going to need to get either an additional live or neutral wire between the floors, lights or switches or bit a both..

depending upon what wires are already there.

Really this sort of problem should be metered out and tested BEFORE starting the CU change!

:Salute

 

[davetheglitz]

Really this sort of problem should be metered out and tested BEFORE starting the CU change!

Out of curiosity how many people check out this before a CU change?

Assume an old Wylex board - neutrals all over the shop. Can't see where the wires come in, and you're looking for a live going through a load (possibly a fluorescent) to the wrong neutral. Sounds a bit of a mission for very little gain. If you do find it - how much does it help?

Ideally you would want the upstairs and downstairs lights on separate circuits - but even if they end up on the same you have improved the situation. If the customer will pay for the extra work done to get the lights on separate circuits - fine - otherwise I'd leave as is.

 

[SPECIAL LOCATION]

Out of curiosity how many people check out this before a CU change? Assume an old Wylex board - neutrals all over the shop. Can't see where the wires come in, and you're looking for a live going through a load (possibly a fluorescent) to the wrong neutral. Sounds a bit of a mission for very little gain. If you do find it - how much does it help?

Ideally you would want the upstairs and downstairs lights on separate circuits - but even if they end up on the same you have improved the situation. If the customer will pay for the extra work done to get the lights on separate circuits - fine - otherwise I'd leave as is.

Even if there are no crosses or joins between circuits.. You have still got

to pair up your live and neutrals to change the CU anyway???

So that aspect has got to be done..

Once you have paired up your Lives & neutrals it is not hard to check if any power is coming back down a wrong neutral..

can be done with continuity testing on dead circuits with all lights switched on...

Bit more tricky if its across florries as you say..

And compounded again with low energy lamps stuck everywhere..

But as we know 90%+ of the cross-overs are on landing and/or hall light bayonet fittings so can concentrate investigation to prove or disprove these specific lamps?.

TBH it is easiest done with a bit of judicious live testing, checking for voltages on disconnected neutrals with respect to the main neutral bar rather than metering out dead continuity through lamps.

And in reality MOST domestics installations even if singles and wylex boards tend to only have TWO or Three lighting circuits at most and maybe 5 or six pairs of cables coming in even on a larger job!

 

[sparkytim]

For a quick check for borrowed N just drop off double gang light switch at bottom of stairs. If only one live feed strapped across both switches, 1 for downstairs hall and other the landing light, then check in landing rose, if single switched live with upstairs L and N looped thru likely thats the problem.

As others have said often easiest to bring N up from ground floor circuit to landing light and remove existing L and N connection into Jb.

 

[steptoe]

and remember if you do have a borrowed neutral and are simple putting both lighting circuits on one RCD, that is NOT good enough,

they must be on one MCB/protective device.

 

[mart1711]

and remember if you do have a borrowed neutral and are simple putting both lighting circuits on one RCD, that is NOT good enough,they must be on one MCB/protective device.

Hi everyone, first post here!!! Good forum by the way..... Been reading through the threads with great interest.. Although we would like the circuits split into upstairs and downstairs i dont actually believe it can be interpreted anywhere in the regs that they must have seperate MCB's(?) If the circuit was labelled just as "lights" and on the relevant breaker and the usual current carrying capacities etc were observed i see no problem. The fact there would be perhaps 2 cables in the top of the mcb is really no different from picking up a different parallel supply from a circuit such as a JB etc.

 

[Sidewinder]

mart1711,

There is a reg that says you must minimise inconvenience in the event of a fault, too much on now to find it, one of the other guys will come up with the number, or I'm sure it will come up on a forum search.

 

[steptoe]

Hi everyone, first post here!!! Good forum by the way..... Been reading through the threads with great interest.. Although we would like the circuits split into upstairs and downstairs i dont actually believe it can be interpreted anywhere in the regs that they must have seperate MCB's(?) If the circuit was labelled just as "lights" and on the relevant breaker and the usual current carrying capacities etc were observed i see no problem. The fact there would be perhaps 2 cables in the top of the mcb is really no different from picking up a different parallel supply from a circuit such as a JB etc.

but you dont have 2 seperate circuits in the case of a borrowed neutral,

you could turn off the MCB for the downstairs lights and the landing light will appear to be isolated,

then you disconnect the neutral and you now have a live cable present.

 

[Zeespark]

130.1 if I am not mistaken, aint got Me BRB near Me.

Andy

 

[davetheglitz]

Once again - good advice on the forum!

Even if there are no crosses or joins between circuits.. You have still gotto pair up your live and neutrals to change the CU anyway???

Thanks Specs - but my point is valid in that you have found the situation after taking off the

old board. As you say you have to pair up the neutrals and lives anyway - however as Steps says

and remember if you do have a borrowed neutral and are simple putting both lighting circuits on one RCD, that is NOT good enough,they must be on one MCB/protective device

. Completely agree.

Thanks for getting me thinking. I tend to do mainly domestic - generally an upstairs and downstairs circuits - so not too much of an issue. However - will try the judicious live testing theory at the next board change!

 

[SPECIAL LOCATION]

Once again - good advice on the forum!

It's ALWAYS good on here?

Guinness

cuz there's people like you! :Salute :xGuinness

However - will try the judicious live testing theory at the next board change!

Its these Modern energy saving lamps and electronic transformer fittings etc...

messing up the old simpletons continuity methods..

You do have to start working around the perimeter of the box to get your job done these days without ripping out every blinkin light fitting to test whats going where!

:Salute

 

[batty]

Suprising how long poor wiring practices have gone on did a lot of work on a house built in the eighties a while back this had the borrowed neutral or was it live can't remember but goes to show it was not only in the sixties so be careful when quoting for cu changes you can get caught out.

 

[steptoe]

was a standard method in the 15th , landing light off DS circuit, N from US,

well for me anyway, :Blushing

even right through to 16th for a lot of newbuilds,

we never had all this new fangled 3c+E so it was usually loads easier to pick the L from the 2gang, run a twin red upstairs and pick the N up there.

 

[Litttle Shonet]

Sorry for the delay in getting back to you all, but this was a job for a friend (Weekends).

Anyway, The Line on the downstairs light switch was powering outside lights, porch light and landing light. Removed line to landing light and fitted new one to that switch. now all ok.

Thanks to all of you that contributed to this thread. Something new learnt again. Thanks again.

LS

 

[msb2003]

Reg 314.2 is the one you want. Not got it here but something along the lines of, "The operation of one protective device should not effect another cicuit and due account of its operation taken into account" Strictly speaking, one RCD and 4 MCB's for example fed through it does not comply to this, and only RCBO's would, but the get out everyone uses is splitting upstairs and downstairs across two RCD's

 

[Robin Spark]

I had a strange one recently where a 1.5mm T&E was connected an old wylex fusebox but the Line conductor was cut back with only N&E connected at the relevant bars.

I found out that it was for one of the hall way lights where a single live was taken from another pendant, but I cant really understand why whoever done this would then run a new cable back to the CU for just N&E, bit strange and a lot more work!

 

[chrishaworth]

Going back to speciallocations post, "Really this sort of problem should be metered out and tested BEFORE starting the CU change!", on a lot of the older boards, this is simply not possible. On most you can't match the neutral to the live/earth until the board is removed because you have a mass of spaghetti, on some of the older ones, you cannot even access the neutral screws before the fuse carriers are removed. Ring mains can be checked out from a socket, but as for the rest, remove, identify, cross your fingers and test.

Cheers. Chris