Why was the RCD not tripping with a N-E short?

[HappyHippyDad]

I went to a property to carry out an EICR.

Sockets and cooker were RCD protected all the other circuits were not.

I realise there is an order of doing the tests but I thought I would check the RCD test button. It didn't trip. I then did an RCD test and the RCD didn't trip.

Took the cover off the CU, started some dead tests on the ring. N-E 0MΩ.

Upon re-energising the ring the RCD kept tripping instantly as you would expect with a N-E short. However all the sockets had been working fine before I arrived!

After an hour of fault finding (as I couldn't leave him without sockets, even though it was just an EICR) I found a neutral touching a back box as the insulation was broken and there was no grommet. Fixed it and the IR results went to 50MΩ and the RCD then worked as it should. I.e the button tripped it and it tested as 11mS at 5x rated current.

My question is why was the RCD test button not working AND why did it not trip when tested? It only became a working RCD once the fault was found which kind of defeats the object!

 

[dinger809]

As with other replies, I’ve had this where I’ve done some work and tested the RCD on its own. Then constantly tripping due to a fault afterwards. I do think if they aren’t tested regularly they get seized and when you do something to send them off, they realise what they’re supposed to do and start working..... especially late on a Friday

 

[Strima]

I've also had it where the customer has kept resetting the RCD until it held. Test button etc had no effect until I isolated and cleared the fault then it would test as normal.

 

[Marti]

Not good enough! You need to find out quick smart and then let me know. I'm too busy making bread and am also about to have a cup of tea!

N-E faults are apiece of cake compared to baking the perfect wholemeal loaf. I think the trick is to knock back the dough mix for long enough; not sure if that fixes RCD issues!

 

[telectrix]

N-E faults are apiece of cake compared to baking the perfect wholemeal loaf. I think the trick is to knock back the dough mix for long enough; not sure if that fixes RCD issues!
View attachment 47845

you going to eat that or use it as a medieval siege weapon?

 

[Midwest]

I prefer Sourdough myself. Her indoors made a massive balls up, didn't get stuff for chilli as instructed; so tonight its shop bought fish & chips or home cooked tuna pasta bake

Perhaps I should of bought her a Valentino Xmas card, or whatever it is.

 

[Marti]

you going to eat that or use it as a medieval siege weapon?

LOAD THE TREBUCHET!

Err... would the OP like their original and useful thread back now

 

[plugsandsparks]

All i can say is if the button does not trip immediately, dont keep your finger on it, especially if working off a ladder... lol