Strange fault

[RF Lighting]

Yep I agree it's very unlikely, but not impossible.

 

[JohnW2]

Yep I agree it's very unlikely, but not impossible.

Indeed. That would be the 'extraordinarily unlikely scenario' to which I was referring

Kind Regards, John.

 

[securespark]

RF: It's just tripped again. Looks like there's another fault....

 

[333rocky333]

Turns out the outside light was also a red herring as the RCD has again tripped a few times since I gummed it up.

I think I've cracked it this time
Found this in the loft connected to the circuit which showed low IR

Rf im a bit stumped here , why would that trip the rcd,

 

[RF Lighting]

Because the vermin gets a shock when it comes into contact with the live part it has exposed and the RCD operates to prevent electrocution as it is designed to do.

 

[JohnW2]

Because the vermin gets a shock when it comes into contact with the live part it has exposed and the RCD operates to prevent electrocution as it is designed to do.

Is there a CPC somewhere in there, then?

Kind Regards, John.

 

[RF Lighting]

No.

Have you ever touched a live wire? What happened?

 

[JohnW2]

No. Have you ever touched a live wire? What happened?

Nothing much - certainly not 30 mA's worth of anything! I imagine that, in the average house, and with average footware, one would be lucky to even feel anything unlpleasant by touching just L.

Kind Regards, John.

 

[RF Lighting]

And if there's already leakage on the circuit?

None of the circuit has a CPC anywhere, and very extensive testing, tracing and rewiring has now been carried out and this is the only thing that we have found that could have caused the problem.

Since it's removal there has been no more tripping.

I have worked on completely different job with an RCBO intermittently tripping. After investigation much of the cable in the sub floor void had been chewed by rabbits. The IR testing showed the circuit was not especially down to earth, except presumably whilst being chomped upon which caused the RCD to trip.

 

[JohnW2]

And if there's already leakage on the circuit?

Well, yes, I suppose that's possible. You could easily test that theory with a few resistors and a path to earth. In fact, a standard RCD test would probably do the same, wouldn't it? Mind you, you'd need to have as many as possible of the 'suspect leaky loads' on-line when you did it.

None of the circuit has a CPC anywhere, and very extensive testing, tracing and rewiring has now been carried out and this is the only thing that we have found that could have caused the problem. Since it's removal there has been no more tripping.

I guess that all adds support to your theory, but maybe you should not count your chickens yet, since it sounds pretty unlikley to me?!

I have worked on completely different job with an RCBO intermittently tripping. After investigation much of the cable in the sub floor void had been chewed by rabbits. The IR testing showed the circuit was not especially down to earth, except presumably whilst being chomped upon which caused the RCD to trip.

Fair enough, but (a) if it were a ground floor sub-floor void, that would be rather different matter, since (even with small rabbitt feet), paths to earth would be much more likely, and (b) more to the point, are you sure that none of those chewed cables had CPCs?

Kind Regards, John.

 

[RF Lighting]

I'll let you know if it trips again, but there was no other visible damage to any of the remaining wiring that we have found.

On the rabbit job the cables did have CPCs. Maybe they were shorting L>CPC rather than L>the ground. Either way it still zapped one of em

 

[JohnW2]

I'll let you know if it trips again, but there was no other visible damage to any of the remaining wiring that we have found.

Thanks. I certainly won't be surprised if it does trip again, but obviously am in no position to suggest what the cause might be if it does. I suppose there's no question that the RCD itself may be getting 'trigger happy'?

I'll On the rabbit job the cables did have CPCs. Maybe they were shorting L>CPC rather than L>the ground.

Quite - that was obviously my initial point.

Kind Regards, John.

 

[RF Lighting]

I'll let you know if it trips again, but there was no other visible damage to any of the remaining wiring that we have found.

Thanks. I certainly won't be surprised if it does trip again, but obviously am in no position to suggest what the cause might be if it does. I suppose there's no question that the RCD itself may be getting 'trigger happy'?

Nope. We transfered each circuit one at a time to a 1 way CU henleyed into the tails until the fault moved RCDs.

 

[pompeygit]

RF did you take home the rabbit and make a nice stew?

 

[RF Lighting]

NO! It had been there a while by time I found it. The smell made me gag and it was full of maggots