Didn't think was possible

[Richard Burns]

If you have a fault from line to earth then this will trip the RCD, it would not matter if the neutrals were in place or not.
You could also have a neutral to earth fault that is then tripping the RCD as the current through the load to the neutral to earth fault will still be enough to trip the RCD.
Since the RCD trips all the time then you need to eliminate anything plugged into the circuit and then test the circuit, there should be a clear and obvious low IR result somewhere.

 

[Pondy]

Ok, I swung by on way home and sure enough the ze at the origin is 3.5 ohms so all four flats are affected. Have emailed my office saying as a matter of urgency we need to contact the supplier.
I always thought that a rcd looked for an imbalance between neutral and earth,and a mcb took care of overcurrent and short circuit and earth fault, hence being stumped after removing all neutrals from the board and even removing the outgoing neutral from the rcd and the rcd still tripping

 

[davesparks]

An RCD does not look for an imbalance between neutral and earth, it doesn't have an earth connection, and you'd have serious issues if there was a balanced current across neutral and earth!

 

[Pondy]

Sorry, I wrote that very quickly and without reading before sending, I meant it measures the return via the neutral which should be equal to the line conductor, any leakage via the earth will trip the rcd.

 

[SirKit Breaker]

You say you havent done the IR testing yet. Instead of clutching at straws, start at the beginning. Do your continuity tests, IR and see what these highlight, it may put you straight to the answer. Generally, if you do things in the correct sequence it may appear to a be bit time consuming, but overall it will generally be quicker than starting in the middle and best guessing, not to mention forgetting what you have already tested. You may find a high resistance that might only be a loose connection, but enough to upset the RCD and trip it out.

Cheers................Howard

 

[guest119]

And don't assume there is always just one fault,there may be more or an accumulation.

Boydy

 

[PEG]

Ok, I swung by on way home and sure enough the ze at the origin is 3.5 ohms so all four flats are affected. Have emailed my office saying as a matter of urgency we need to contact the supplier.
I always thought that a rcd looked for an imbalance between neutral and earth,and a mcb took care of overcurrent and short circuit and earth fault, hence being stumped after removing all neutrals from the board and even removing the outgoing neutral from the rcd and the rcd still tripping

Hi Pondy,an RCD does monitor and operate due to an imbalance,but between line and neutral,this may be shootin' up THE earth,or AN earth,but it determines "some",maybe 30 ma's worth is awol,and operates accordingly. The advice concerning the order of tests is sound,and although on occasion skipping some can still bring a quick result,in general it negates back-tracking. Happy hunting.