Strange RCBO behaviour (MEM)

Adam_151 · Posted: Wed Sep 02, 2009 6:57 pm Post Subject: Strange RCBO behaviour (MEM)

I generally test RCBOS at the DB rather than at the end of the circuit, but came across something weird today RCBOs failed when I tested them at the board (even with the circuit connected), but worked fine when I tested them from a point on the circuit.

Completely threw me, it doesn't make sense to me, anyone?

ColJack · Posted: Wed Sep 02, 2009 7:04 pm Post Subject:

these the MEM ones with the "pod" on them?
the rcd works by a non contact CT round the live wire.. ( as I just explained in another thread ) , so testing at what is in effect the breaker screw will miss out the CT "tube"..

__________________
If you make everything idiot proof, evolution will just make a better idiot.

JohnD · Posted: Wed Sep 02, 2009 7:48 pm Post Subject:

what's "CT"?

ColJack · Posted: Wed Sep 02, 2009 7:53 pm Post Subject:

sorry, CT is Current Transformer.. ( I think.. )

coils that you put around a wire..
a voltage is induced in the coil relative to the current flowing through the wire..

__________________
If you make everything idiot proof, evolution will just make a better idiot.

Lectrician · Posted: Wed Sep 02, 2009 7:54 pm Post Subject:

Current transformer.

This is well known with the MEM RCBO's (even the MCH and ALB off the shelf range rather than field fit pods).

JohnD · Posted: Wed Sep 02, 2009 7:55 pm Post Subject:

gotcha, thanks