RCD trip help

[sirocco]

Just been called out investigate RCD tripping on downstairs ring at my parents it just went in the early hours with no history. Have unplugged all appliances from the 10 sockets on this ring and switched all sockets off. There are no other appliances fed from this ring other than those plugged in via sockets. There are 3 other circuits protected by the same RCD in the CU ie Shower, Cooker and upstairs ring, these are all functioning normally and don't trip the RCD. I have substituted the downstairs ring MCB but the circuit still trips the RCD immediately when the MCB is switched on with nothing plugged into the sockets. My next step is to disconnect the ring, split the dead ring at the midpoint and test each half, but before doing this I removed the 2 CPCs for the ring at the CU from the earth bar and the circuit now stays on and doesn't trip. Before I plough on , disconnect the phase and neutrals and do dead circuit testing is there anyway that I can identify why the disconnection of the CPCs allows the ring to operate? Graham

 

[KAS1]

He's lost me, it looks like a step by step guide to nowhere IMO lol

 

[dave1064]

Sounds like a line to earth fault. Insulation resistance test should find this out.

 

[babylonsBurning]

Hey Dave
Im guessing u are new to this thread, most of us said exactly this.
Then something weird happened, if you want a laugh read all the previous posts and you will be as confused as the rest of us!!!!!!!

 

[Outspoken]

Just been called out investigate RCD tripping on downstairs ring at my parents it just went in the early hours with no history. Have unplugged all appliances from the 10 sockets on this ring and switched all sockets off. There are no other appliances fed from this ring other than those plugged in via sockets. There are 3 other circuits protected by the same RCD in the CU ie Shower, Cooker and upstairs ring, these are all functioning normally and don't trip the RCD. I have substituted the downstairs ring MCB but the circuit still trips the RCD immediately when the MCB is switched on with nothing plugged into the sockets. My next step is to disconnect the ring, split the dead ring at the midpoint and test each half, but before doing this I removed the 2 CPCs for the ring at the CU from the earth bar and the circuit now stays on and doesn't trip. Before I plough on , disconnect the phase and neutrals and do dead circuit testing is there anyway that I can identify why the disconnection of the CPCs allows the ring to operate? Graham

Could call out an experienced Electrician I suppose...this should be a doddle to locate the fault. As others have said it is clearly an L-E fault so finding it should be straight forward, if a pain in the rear, so I do not get the coming here asking help to solve something that should be solvable by a decently trained 3rd year apprentice...

 

[sirocco]

Sorry got to be quick, but if you removed cpc,s from met, tested IR, then how would you know if there was a fault from a live conductor to any extraneous metal in that installation?
Therefore by keeping the cpc's in the met and putting your test lead on that and your other lead on the circuits L or N, then you will be verifying that all earth parallel paths are isolated from live conductors.

Very Good point esp if carrying out an Ir on a full installation. If you've narrowed the problem down to one ring and need to check Ir on wiring between sockets , would it still be best to leave the cpcs connected I the sockets and just remove the conductors between the suspect sockets to Ir check LE and LN leakages?

 

[guest119]

Power Ranger, it has already been confirmed that there are no parallel paths at the start of this saga as the rcd tripped no more when the naughty boy took the cpcs out of the met.
The lesson in this thread is that you can take a horse (aka Electrical Trainee) to water but you cannot make it drink.
Oops, no, I dont have a horse parked outside customers houses, said it before Biff.

Boydy

 

[dave1064]

Ah lesson learned today: read all posts in a thread before posting myself.

Just an IR test between line and earth was the most logical thing to do. .. I dont understand why this was not carried out.

First thing to do should have been an IR test...

 

[power ranger]

Power Ranger, it has already been confirmed that there are no parallel paths at the start of this saga as the rcd tripped no more when the naughty boy took the cpcs out of the met.
The lesson in this thread is that you can take a horse (aka Electrical Trainee) to water but you cannot make it drink.
Oops, no, I dont have a horse parked outside customers houses, said it before Biff.

Boydy

Boydy, Yes of course, your right on that count in that its obviuosly a L-CPC fault on this circuit. So apologies if I caused a bit of confusion on the thread as Sirocco would still have found the fault doing IR tests with the CPCs disconnected at the MET.

However, if he had removed a few sockets including the one with the fault on it before doing any IR tests then he would have probably cleared the fault on this occassion and so would have not found anything wrong. Therefore, I probably now guess that as the RCD is holding on that the fault would now be only found on close visible inspection of the Line conductor insulation at each outlet.

But what I was originally getting at, is that quite a few electricians do their IR tests with the CPC's isolated from the MET and I just got the impression that Sirocco always did this as part of his normal testing procedure.

 

[JB30]

rcd help!

When i rcd test with my fluke meter it works on some circuits and on the rest it reads 310.0 Ms an wont trip!! Wots up?? Please help!

 

[Deleted member 9648]

Re: rcd help!

When i rcd test with my fluke meter it works on some circuits and on the rest it reads 310.0 Ms an wont trip!! Wots up?? Please help!

How are you testing? more info needed.
Not familiar with the fluke but it's probably going over-range at 310ms. Make sure all loads are disconnected before testing,as these can cause longer trip times,particularly loads with a capacitor.

 

[lewlec]

Hi
Have this with my fluke occasionally, only when I test at rcbo/ rcd but if test at end of circuit it works ok. Hope this is of use.
Regards
Gary

 

[Engineer54]

Hi
Have this with my fluke occasionally, only when I test at rcbo/ rcd but if test at end of circuit it works ok. Hope this is of use.
Regards
Gary

Which goes against virtually all of the RCD/RCBO manufacturers testing procedure recommendations!!....