RCD tripping at half current

[elementps]

Hi all,

Wondering if anyone could throw a few suggestions my way.

Was testing a few circuits last week in preparation for additions (extension of house). All going fine until i tested the RCD that the customer currently has installed, it tripped on half current test?

I am planning to go back for some further investigation.
I tested at socket outlet, so my first idea is test direct at consumer unit, possibly dissconect the load??

The board is MK with MCB's but slightly older, the new MCB's will need a busbar conversion to fit. It's a split load with the RCD covering sockets, one think that threw me was the RCD is 4 module, is this just how they were made? All i can see from MK catalogue in 4 module, is 3 phase equipment???

Customer didnt really want to change board, but I think its heading that way as changin mcbs to rcbos, converting busbar, possibly replacing rcd is all adding up. May as well fit a new board.

Any ideas/advice on reasons for the RCD trip appreciated.

 

[Amp David]

I'd would test again with all loads disconnected like you say, then see what you get.

All loads should be removed anyway, all mcbs from that RCD off. If it still trips then its probably faulty

 

[malcolmsanford]

If you tested at a socket you may have had loads plugged in that would affect the result, though normally that would just give you inaccurate times on the X5 test.

I would be going towards a either a dodgy RCD, or if you had loads plugged in that had Protective Conductor currents on them.

As you know a 1/2 test puts a 15mA fault on the RCD so if it dodgy then it could trip at this, so do a ramp test and see what it is tripping at.

If you left loads on it, that did have protective conductor currents, then the 15mA may have been enough to trip it. So test it at the CU.

 

[elementps]

Sorry forgot to mention, did a ramp test, at socket, 17mA.

So as planned I will first discon everything and test at board.

Now if this is still bad readings obviously faulty RCD, however what should be my next plan of attack if its not?

 

[malcolmsanford]

17mA is quite low and I would be looking at replacing that. Just to make sure that there is nothing affecting the RCD do a ramp test at the board.

Just open all the MCB's and with the RCD left closed test on the supply side of the RCD.

 

[Octopus]

Me thinks that a CU change would be an ideal recommendation in this instance.