RCBO not tripping on RCD test

[willelec]

Hello

I’ve been carrying out an EICR today and have come across a problem. The property is a small upstairs flat.

I’ve carried out dead tests which all came back good.. no problem on IR. There is some ‘green goo’ present in some switches but it all meggers fine.

The lighting is on a 6A 61009 rcbo 30ma serving 9 points.. including 12v fan.
It is a TNCS system and I have a ZE of 0.21.

When I tried to carry out ZS at a pendant the rcbo trips within about 2 seconds of the test starting. I then try to do an auto rcd test which won’t trip at 1 times. I’ve replaced the rcbo for a new one and still no joy. I’ve tried doing each test seperatly at 1x and 5x but it’s not tripping at all. The functional test on the rcbo works as it should.

I can’t seem to see what the problem could be? Has anyone come across anything like this before? Any help would be great as I am returning tomorrow to finish.

 

[Andy78]

Does the RCD behave correctly when tested with loads disconnected like you're supposed to ?

 

[Deleted member 9648]

As above, test with loads disconnected.

 

[Pete999]

As above, test with loads disconnected.

As above twice

 

[telectrix]

and thrice.

 

[Octopus]

Have you tested for IR ?

I would suggest you have a fault to find

 

[Dave OCD]

A neutral to earth low IR fault will cause this.

 

[Acmacm]

Might be worth doing a pscc and pefc at origin 1st. then pfc at distro board before checking further up the circuit

 

[Baker1988]

Are you doing the test at the rcbo its self or at a point in the circuit?

 

[buzzlightyear]

are you testing with the three wire from the tester or two wire ?

 

[Midwest]

That's rather strange, OP posted and then went off-line? Perhaps he seen what happened on that other thread! Hope he's sorted now.