N-e fault on non RCD side of db tripping RCD???

[bigbaddave]

As above... Possible?

 

[telectrix]

yes... next question?

 

[bigbaddave]

No further question needed. That clears that up. Ta

 

[UKMeterman]

Hi,
I am curious, could someone please explain how a N-E fault confined to the non RCD side of a board could trip the RCD, given that N-E is joined at the TX, or cutout...

 

[telectrix]

N-E faults can cause some weird effects. i had one where a N-E fault on 1 side of a new dual RCD CU stopped both RCDs from tripping, even with the test buttons, but when a load was applied to either side, both RCDs tripped.

 

[HappyHippyDad]

Richard Burns drew a good diagram once that 'I think' showed how this would be possible but I cant find it. I cant understand how it can happen though (from a N-E fault) as the only connection between the non RCD side and RCD side is from the supply L and N in the top of the RCD, so even if there is a current imbalance on the non-RCD side how can this impact on the RCD as none of the current has been flowing through the RCD?

 

[TJ Anderson]

Hi,
I am curious, could someone please explain how a N-E fault confined to the non RCD side of a board could trip the RCD, given that N-E is joined at the TX, or cutout...

I was thinking exactly the same thing to be honest.

 

[TJ Anderson]

N-E faults can cause some weird effects. i had one where a N-E fault on 1 side of a new dual RCD CU stopped both RCDs from tripping, even with the test buttons, but when a load was applied to either side, both RCDs tripped.

Out of interest, did you have a short N-E or low insulation resistance N-E when you had this?

 

[telectrix]

TBH, i forget. think it was close to a dead short.

 

[Deleted member 26818]

No, not possible, unless there is also a fault on the RCD side.
Current will flow along any and all available paths.
RCDs operate by detecting imbalances between Line and Neutral.
A N-E fault on the RCD side, will cause some of the current which would flow along the Neutral conductor, to flow along the Earth conductor. bypassing the RCD.
As such the RCD will detect that there is more current flowing along the Line conductor, than along the Neutral conductor, and operate.
An N-E fault anywhere else cannot affect the amount of current flowing along the Line and Neutral conductors attached to the RCD.

 

[rich.250]

Unless you have a borrowed neutral....
Shared between the rcd & non rcd side.

 

[PEG]

Yep,the "connection" between differing sides of such a board,may be due to other,"off-board" reasons. The tripping being just the start of that illuminating journey :icon12: