lighting circuit problems

[glasgospark]

upgraded board to dual rcd
everything ok
that night lighting circuit breaker trips rcd stays on
i go back try putting breaker back on trips after a couple minutes , every light in house working when breaker on
tried disconnecting all outside lights etc, also still tripped with every light switch in off position ,
after numerous attempts trying different things the rcd then tripped along with the mcb , now rcd wont stay on when lighting mcb is on everything else in house is ok , i have tried a different mcb for lighting and still happens , it also stayed on for 4 hours yesterday untill ittripped that night ,

no timers on circuit or anything

any thoughts

 

[telectrix]

get your tester out.

 

[glasgospark]

get your tester out.

Done a ir test joined live and neutral and tested to earth , got 0.02

 

[telectrix]

so, do the same on continuity, get an idea of the resisiance. then start opening fittings and switches. could be a trapped cable or a screw into a cable.

 

[Dizzy_Maskell]

Get the IR meter on the case check no issues, are all neutrals in the correct order?
I had a similar issue once turned out to be a damaged cable below a floor board IR was >5 meg but when someone stood on the floor board it caught the nail below lucky find in the end,
I would love to meet the plumber who caused it

 

[glasgospark]

so, do the same on continuity, get an idea of the resisiance. then start opening fittings and switches. could be a trapped cable or a screw into a cable.

You suggest r1r2 every point , not done that yet , firstly it was McB only and would trip after minutes now rcd and it won't stay on atall

 

[telectrix]

check the nail. if it's been put in with the nail head at the top, can't have been a plumber. probably a wood butcher.

 

[Guitarist]

When you upgraded the board, did you not carry out a full spread of tests on every circuit?

 

[glasgospark]

Get the IR meter on the case check no issues, are all neutrals in the correct order?
I had a similar issue once turned out to be a damaged cable below a floor board IR was >5 meg but when someone stood on the floor board it caught the nail below lucky find in the end,
I would love to meet the plumber who caused it

Funny you should mention that , when it was just the McB tripping 2 times in a row at a squeaky floorboard when stood on it tripped straight away but after that nothing now it's rcd , which made me think its worked its way through the neutral cable now causing Imbalance on circuit and not a dead short ,

 

[Richard Burns]

If the MCB trips after a few minutes it is either carrying about twice the rated current or something is heating up and then causing a fault. Clamp test the circuit of it can stay on and check the load.

Once this fault has occurred several times the expanding damage has now involved the cpc and caused the RCD to trip.

Split the circuit and IR test the sections until you can narrow down the location.

 

[glasgospark]

If the MCB trips after a few minutes it is either carrying about twice the rated current or something is heating up and then causing a fault. Clamp test the circuit of it can stay on and check the load.

Once this fault has occurred several times the expanding damage has now involved the cpc and caused the RCD to trip.

Split the circuit and IR test the sections until you can narrow down the location.

It's only pulling 2.8amp full load , I took earth out the circuit also and it stayed on for 4 hours then tripped , of course not a solution but I was testing the waters

 

[telectrix]

you really need to split the circuit down and IR test in sections. only way.

 

[Guitarist]

It's only pulling 2.8amp full load , I took earth out the circuit also and it stayed on for 4 hours then tripped , of course not a solution but I was testing the waters

Was that a safe thing to do?

 

[glasgospark]

Was that a safe thing to do?

Of course not but full house is class two fittings and switches etc , and was only for temporary testing

 

[oldtimer]

If the MCB tripped and the RCD stayed on then initially you had a L-N fault so as advised check the whole circuit because I think you have agrivated the situation when you were switching the MCB on.

Also what was the point of this did you hope the fault would go away ?

 

[KAS1]

You'd be just as quick to of disconnected all lights(there can't be many if this is domestic we are talking here) on the circuit and from the DB and has been said even if it means testing from point to point you will find the fault it may be at a termination or cable damaged it's not rocket science, you may even have to replace a length of cable God forbid, but find it you must you'll get there in the ,just break the circuit down.

 

[Dizzy_Maskell]

^^^^^Long road but only way solve it properly as said above

 

[Guitarist]

You'd be just as quick to of disconnected all lights(there can't be many if this is domestic we are talking here) on the circuit and from the DB and has been said even if it means testing from point to point you will find the fault it may be at a termination or cable damaged it's not rocket science, you may even have to replace a length of cable God forbid, but find it you must you'll get there in the ,just break the circuit down.

Had the same thing a while back, builder had put a screw through a cable when fixing a batten up for a new ceiling. Disconnected the whole circuit at the first rose, then added and IR tested as I went until the faulty leg of cable showed up. Fairly straightforward to find after that.

 

[Guitarist]

You suggest r1r2 every point , not done that yet , firstly it was McB only and would trip after minutes now rcd and it won't stay on atall

I always R1+R2 at every point when carrying out a CU change. Amazing how many times I've found breaks in the cpc which must have been there for years.

 

[davethsparky]

Whats with this test each bit individually malarky? Split the circuit in half find the faulty half, split the faulty half and find the faulty half of that etc etc until you isolate the fault.