Help needed with an RCD question

[vickery1971]

Hello again, as usual I need some advice from the learned amongst us. I went to a job today with the customer saying he was reading a book and the RCD tripped. When I got there he had sussed that it was the RFC in his flat and had turned that circuit off. I unplugged all appliances and it was still tripping. I then began to check the circuit out to check for a faulty socket or water ingress. To cut a long story short I ended up sussing that the RCD stays on until it is under load, it seems that the oven circuit (on its own circuit and working fine with the oven) but if you plug any appliance into the cooker switch it trips as soon as there is a load. I then thought it may be the RCD. When I tested the RCD I got >51ma on a ramp test and 1x >40 and 5x >400. I then changed the RCD for a new one and got the same readings. I have tested with all loads disconnected and still the same.


Answers on a postcard

 

[Deleted member 72666]

Ze of 0.01!
Blimey you could have some massive PSSC. Probably nothing to do with your problem but that is an extremely low Ze. What's the breaking capacity of the mcbs etc?

You get low readings like that when you don't disconnect main earthing conductor for test.

 

[bartkusal]

Ze of 0.01!
Blimey you could have some massive PSSC. Probably nothing to do with your problem but that is an extremely low Ze. What's the breaking capacity of the mcbs etc?

Tell me about it, its like 24.1 kA, if to go by mesured 241V, your gear would not handle that, its like 4 times braking capacity of your standard 6 kA mcb, I think you ment Ze=0.10 ohm ....

 

[vickery1971]

Thanks for spotting the type o guys, 0.1 it was, going back for IR tests when he is out.

 

[Outspoken]

Reading through this thread I noticed there was an issue if the socket on the cooker plate was used under load....Have you considered checking the cooker switch, cooker connection and the actual cooker itself, these things are bad at causing RCD issues..