Rcbo paranoia

[sevuk]

Rcbos haven't caused me much concern before but I'm wiring a board of 44 and it's triggered my paranoia. I've also sent the below to schneider.

I normally just disconnect the line and neutral for testing between live conductors and then test lives to earth with the earth tail of the rcbo and earth conductor still connected to the earth bar at 500v

My question is this correct? Could the test still be carried out in an isolated board with the neutral still terminated in the rcbo but the line disconnected. (Basically to clip onto the neutral bar and test individually to each disconnected line.)

Also the reverse could insulation testing be done with the neutral disconnected from each rcbo to test the insulation between phases?

From a technical point of view are we just trying to avoid putting the meter between line and neutral while both are connected as it's the potential between these that could damage the unit? And does it matter in any circumstance that the earth is connected?

 

[Octopus]

If you IR test a RCD or a rcbo you will get very low results...

So best avoid multiple IR tests together.

 

[sevuk]

If you IR test a RCD or a rcbo you will get very low results...

So best avoid multiple IR tests together.

Quite sensible really. I talked to schneider, they want you to disconnect every rcbo entirelt to do insulation resistance tests. With a fully populated board you'd have to disconnect all of them to do an IR. This is madness right?

If you were to disconnect line and neutral why would it be adverse to then ir test live to earth it's still connected to the rcbo? There's no voltage across the core with the lives disconnected.

 

[Octopus]

With a fully populated board you'd have to disconnect all of them to do an IR. This is madness right?

Well, as a fan of RCBO's I don't see this as a problem ......... and if you are testing due to the RCBO testing, you need to do this on the circuit affected ..................... to get accurate results...

 

[sevuk]

Thinking about it you're right. It normally wouldn't be a big deal but there are 44, though still not the main issue. It's a board with all the earth terminals at the top and the guy before me glanded all the armoureds to the top instead of mounting a trunking on first making the earths a pain to disconnect and reconnect.

What I mean is if the live conductors are disconnected, there's no path to earth so I can't see why you'd get a reading to earth unless there was a fault or insulation degradation. You would get readings if you tested to the neutral bar though.

Anyway in the installation phase there would be ways to ir test the circuits first before connecting them to the rcbo, but during service if you had to disconnect even the earth doing any ir tests require full isolation of the board which wouldn't be practical.

 

[ipf]

Paranoia RCBO's.....who make them?
Innovative name...must be Chinese!