RCBO only latches under load?

[lilman]

Replaced a distribution board today - including 4 fluorescent lighting circuits on RCBOs (30mA/6A/type C). For some reason one of the RCBOs will only latch with the lights on; it then operates fine - tests OK (did try another also just to be certain). Also noticed that when the test button on a neighbouring RCBO was pressed it occasionally trips this one. What's occurring - any ideas?

 

[a1spark]

Lilman did you carry out IR testing of the circuits

 

[lilman]

Yes I did - all OK

 

[a1spark]

If you replaced it with another rcbo and it still trips it sounds like an insulation fault to be honest lilman.

 

[binky]

Is it my imagination, or do RCBOs behave a bit different to RCDs????

 

[sparkytim]

The O in RCBO means it has Over current protection as well as earth leakage

i.e. its a RCD + MCB in one, so yes it can trip not only as an RCD but also for Overload or short circuit faults that an RCD would not trip for.

 

[Chr!s]

Sounds like a neutral to earth fault, Check non of the lights are switched in the neutral.

regards chris