RCD mystery

[crystal ball]

Did a CU swap this week, dual RCD BG 16 way, I tested the second RCD, it would not reset, switched power off still no reset, disconnected it and it reset, fitted back in the CU it tripped with power off, still not resetting

I took the same type RCD out of my garage unit and fitted it in the CU all good, fitted the tripping RCD in my garage all good ????

 

[Adam_151]

The fact that it would not reset with the power off means this is a mechnical problem rather than electrical. I would suggest that perhaps the mechncials were a bit marginal on the original RCD and when fitted in the DB the strain on the terminals pulls it a little out of line, but release it and it works fine out of the board. Perhaps things are a little less strained in the garage board.

I've certainly seen similar on a 4 pole RCD in a plastic enclosure on a farm, tails cable through 4x m20 stuffing glands (plastic enclosure), the spacing of cable entried was wider than the poles on the RCD, but because both were centered about the middle of the enclosure, no terminal was too far out that a tail could not be entered through the gland, guided slightly over to its terminal and suggestfully tightened down. The RCD would not reset, even with no power. But take it out and its fine. Once the tails were re-dressed with a small set so they were in the RCD witghout applying sideways loading, the problem was no more

 

[crystal ball]

My thoughts too, never seen it before though

 

[ericmark]

I have in the past had it where bus bar or stiff cables have warped the plastic casing causing RCD problems.

 

[delmel]

Sure you have not got a neutral connection to the wrong terminal bar. If its Dual and you have added something, make sure neutrals are in the right one or it will trip all day every day

 

[Taylortwocities]

Did the RCDs pass the RCD testing at ½, 1 and 5 times Δn ?

 

[crystal ball]

Never got chance to test it in situ, the existing one was ok and the one in my garage has been fine

 

[Taylortwocities]

So, you changed a CU and did not carry out the required tests - which includes full tests of the RCDs?

I have no sympathy.

 

[crystal ball]

If you read my initial post properly, instead of jumping in with both feet you will realise what happened

 

[crystal ball]

So, you changed a CU and did not carry out the required tests - which includes full tests of the RCDs?

I have no sympathy.

Perhaps TTC can inform me how to test an RCD that will not reset?

 

[Harry Bloomfield]

I would suspect the neutral as being the cause.

 

[crystal ball]

Did a CU swap this week, dual RCD BG 16 way, I tested the second RCD, it would not reset, switched power off still no reset, disconnected it and it reset, fitted back in the CU it tripped with power off, still not resetting

I took the same type RCD out of my garage unit and fitted it in the CU all good, fitted the tripping RCD in my garage all good ????

 

[oldbutnotdead]

I had a similar issue with a recent 16 way board (not BG, brand was 3 letters). Excess lateral strain on the RCD terminals would explain the way that one went as well (circuits all fine, RCD fine on the bench and fine after refitting with more care taken setting the tails in & out of the RCD)

 

[crystal ball]

Yes can only be that, all been fine AFAIK not been back since, and the RCD in my garage is holding, still wondering how to test an RCD that will not reset though

 

[bernardgreen]

still wondering how to test an RCD that will not reset though

If it cannot be reset then surely it has failed the functionality test.