Suitable RCCB replacent

[telectrix]

a N-E fault on a circuit may inhibit the RCD from operating, both on testing with MFT and the test button. had it a couple of times. once was on an immersion heater cable with a nail in it. once i had dissed the cable from the board, the RCD worked perfectly. on testing the cable, it was a dead short N-E so there was no volts N-E either.

 

[gazdkw82]

a N-E fault on a circuit may inhibit the RCD from operating, both on testing with MFT and the test button. had it a couple of times. once was on an immersion heater cable with a nail in it. once i had dissed the cable from the board, the RCD worked perfectly. on testing the cable, it was a dead short N-E so there was no volts N-E either.

I'll be honest, I dont get that. Iv had rcds that wont hold in because there is a neutral to earth short.

What neutral to earth characteristics would denote an rcd tripping and an rcd not operating at all? Earthing arrangement? Extent of short circuit?

 

[MJPD29]

a N-E fault on a circuit may inhibit the RCD from operating, both on testing with MFT and the test button. had it a couple of times. once was on an immersion heater cable with a nail in it. once i had dissed the cable from the board, the RCD worked perfectly. on testing the cable, it was a dead short N-E so there was no volts N-E either.

Had that too. A bit of head scratching went on before I realised what it was. Disconnected circuit and RCD was fine.

 

[telectrix]

it's weird. i can't explain the science behind it, but it does sometimes occur.

 

[gazdkw82]

it's weird. i can't explain the science behind it, but it does sometimes occur.

How odd, taking into account the theory behind rcds, any neutral to earth should operate the device. I cant imagine any condition where the rcd would not see an imbalance when neutral and earth are shorted in some way....

I think by process of elimination I will still try what you have suggested and rule out neutral to earth fault

 

[suffolkspark]

It can occur if the N E fault is on a non rcd circuit in the same board, somebody once had a link to a diagram of how it occurs

 

[telectrix]

might be on a PME system, the N-E fault could case current to flow through E to MET and as this is strapped to N at the cut-out, backfeed through N to the RCD inhibit it from tripping. only a guess mind. as for above post. if i recall, it was a dual RCD board in one case and both RCD faied to trip.

 

[DefyG]

Dont expect something of that age to be cheap

Was quoted over £200 for a Sq D / Schneider replacement RCBO! .......It was cheaper to replace the board!