New Workshop CU - Instant Trip with Main Switch On"

[TheAverageJoe]

I'm having an issue with a new consumer unit (CU) in my workshop. The feed comes in via a 32A RCBO, and continuity tests between L-L and N-N are good. I even get a voltage reading at the workshop's main switch.

However, the 32A RCBO trips instantly the moment I switch on the new workshop main switch, a BG Electrical 100A DP Main Switch (CUSW100). This happens even with absolutely no loads connected to the output side of the main switch – the DIN rail and neutral are completely disconnected.

Could this be a dead on arrival double-pole main switch? Any insights or similar experiences would be greatly appreciated!

 

[pete01]

Sounds like a shorted main switch...but if it was it would go with a bang.

 

[Murdochcat]

Who fitted it?

 

[JohnD]

Show us some photos

 

[TheAverageJoe]

Thanks for the replies, maybe the DP switch is DOA and has the short since it instantly trips the house 32A RCBO. A new CUSW100 is not too expensive to test I guess. Will look at getting some pictures to help

 

[Harry Bloomfield]

However, the 32A RCBO trips instantly the moment I switch on the new workshop main switch, a BG Electrical 100A DP Main Switch (CUSW100). This happens even with absolutely no loads connected to the output side of the main switch – the DIN rail and neutral are completely disconnected.

Assuming the RCBO is in the house, and the main switch in the workshop CU, and further assuming you can switch on the RCBO, but as soon as you switch the main switch on, then the issue must be in the CU. Either a faulty main switch, or a fault within the wiring in the CU. Have you checked with a meter of some sort?

 

[Murdochcat]

Damaged cable from the main CU

 

[pete01]

Damaged cable from the main CU

The rcbo wouldn't switch on then would it?

 

[ericmark]

continuity tests between L-L and N-N are good.

What about insulation between them and earth, I would be looking at a neutral - earth fault.

I remember looking at a friend's compressor, had multi-meter to hand, no fault found, but when I used insulation tester at 500 volts, showed near short circuit.

 

[pete01]

What about insulation between them and earth, I would be looking at a neutral - earth fault.

How? A main switch doesn't have an earth connection.

 

[securespark]

Pictures of the supply end and the garage C U could well help.

 

[ericmark]

How? A main switch doesn't have an earth connection.

I have worked on an IT system once, a Robin TBM, other of course to bathroom shaver sockets, but most electrical systems are either TN or TT and do have a connection to earth somewhere.

And believe me, IT systems are not nice, walking around with a tester so you even need to test a handrail before touching it is not nice.

 

[pete01]

I have worked on an IT system once, a Robin TBM, other of course to bathroom shaver sockets, but most electrical systems are either TN or TT and do have a connection to earth somewhere.

And believe me, IT systems are not nice, walking around with a tester so you even need to test a handrail before touching it is not nice.

I'll have to take your word for it, never worked on an IT system.

 

[Ragnar_AT]

If the load side terminals of the main switch are disconnected I can‘t see how there could be a N-E fault. Now if the link to the neutral bar was connected, a low-impedance N-E fault combined with enough voltage drop on the neutral from loads at the house could be enough to make a 30 mA RCBO trip.

 

[securespark]

Pictures of the supply end and the garage C U could well help.

This....