Tripping RCD since testing?

[HappyHippyDad]

I have literally just had a phone call from the customer I saw today after doing an EICR and he says one of the RCD's is now tripping every half hour or so.

There were 3 CU's in total so I am back tomorrow to finish off. I didn't have time to test each circuit on the third CU but I did find poor global IR readings (L/N - E) of 0.008MΩ.

Trip time for the RCD was 43mS.

Its a TT with a Ra of 43.4.

He is currently having the property replastered (ongoing) this could be the reason for the poor IR, but I cant understand why it is tripping now when it wasn't before. He seems like an honest chap so I believe him.

I always spend the last part of the day making sure connections are tight so I'm pretty sure thats not the problem.

I'll break the circuits down tomorrow and find the culprit, but it was more the fact thats its tripping now and (most likely) wasn't before that I can understand and could do with a few opinions?

 

[Tiny Spark]

One of them could be anything things I would think.

Few ideas could be a weak mech that now wont hold after you tested it?
If the house is currently being plastered wet plaster shorting out something?

Sure some of the others will give you some other/better ideas

 

[Desrebel]

Sounds like a neutral to earth , if it's holding when you flick the rcd back on then I imagine it's tripping when a load is connected and the heat builds up . I've had it before when all is reading clear and holding and then as soon as anything is connected it trips nightmare

 

[telectrix]

afraid that without being there it's just guesswork. sod's law says it's tripping since you were there. only thing is for you to go back and trace the fault. let us know what you find.

 

[telectrix]

and never, ever, believe a customer when he says that it was all right before you touched it.lol.

 

[Octopus]

I'd retest the IR on the "suspected" circuit, repeating the test quickly to see if the IR increases - if it does it would suggest damp. All you can do then is wait for it to dry.

Plastering does mean that A LOT of moisture is "tracking" across the surfaces so good luck finding it!

 

[HappyHippyDad]

I feel a bit of a --- adding this next bit and wasn't going to but you need all the information!

I was tired and tested at 500V by accident and got about 0.04MΩ, then tested at 250V and it went lower (0.008MΩ) which didn't make sense, unless it's the putting 500V through that did it?

I'm sure it was ok after that for an hour or so though (before leaving)! The very last thing I did was test the RCD, can actually testing the RCD produce problems?

 

[Octopus]

I feel a bit of a --- adding this next bit and wasn't going to but you need all the information!

I was tired and tested at 500V by accident and got about 0.04MΩ, then tested at 250V and it went lower (0.008MΩ) which didn't make sense, unless it's the putting 500V through that did it?

I'm sure it was ok after that for an hour or so though (before leaving)! The very last thing I did was test the RCD, can actually testing the RCD produce problems?

I would doubt it unless you shoved 500V up it.

I'd ramp test the RCD again.

Sometimes, when its late you go round and round in circles, so walking away and going back tomorrow, with a clear mind, is probably the best plan

 

[HappyHippyDad]

I'd retest the IR on the "suspected" circuit, repeating the test quickly to see if the IR increases - if it does it would suggest damp. All you can do then is wait for it to dry.

Plastering does mean that A LOT of moisture is "tracking" across the surfaces so good luck finding it!

Thanks Murdoch..

Could you explain this a little please?

 

[Tiny Spark]

Testing at 500v isnot a problem as long as all electronic equipment is shorted or removed. Otherwise it will just damage the item that is not. (Blown a neon or 2 on spurs doing this )

Not sure about RCD's but like I said before it could be a weak mech, We worked on a circuit once and when we put the MCB back on it just wouldnt hold despite everything being tested ok. Changed it for a new one and it held fine.

 

[Octopus]

Thanks Murdoch..

Could you explain this a little please?

If the 500V test is repeated and the IR value increases, it suggests that the 500V is actually "drying" the moisture - hope this makes sense

 

[Paul.M]

I'd take a new RCD with me in the morning as said above.

 

[HappyHippyDad]

I would doubt it unless you shoved 500V up it.

I'd ramp test the RCD again.

Sometimes, when its late you go round and round in circles, so walking away and going back tomorrow, with a clear mind, is probably the best plan

Very true Murdoch! I realise 9 hours probably isn't very long for some sparks.. but I was a bit on the tired side.. even after a quick fix of chocolate and coffee!

Testing at 500v isnot a problem as long as all electronic equipment is shorted or removed. Otherwise it will just damage the item that is not. (Blown a neon or 2 on spurs doing this )

Not sure about RCD's but like I said before it could be a weak mech, We worked on a circuit once and when we put the MCB back on it just wouldnt hold despite everything being tested ok. Changed it for a new one and it held fine.

Thanks Tiny.. If all else fails I'll change it, but I'll get to the bottom of the low IR readings first.

 

[GMES]

Agree with Murdoch I have done the same thing many times, think of it as an expensive hair dryer

 

[Tiny Spark]

Very true Murdoch! I realise 9 hours probably isn't very long for some sparks.. but I was a bit on the tired side.. even after a quick fix of chocolate and coffee!



Thanks Tiny.. If all else fails I'll change it, but I'll get to the bottom of the low IR readings first.

Good plan bat man