What are the implications of a failed Neutral - Earth insulation resistance test?

[markusjames]

It's not clear what the OP is testing. Is it the 3-phase supply cable from the distribution board to the dimmer rack? Is the rack still connected to the cable? Are the outgoing lighting circuits still connected to the dimmers?

Again, what make and model of rack is it?

Is it the 3-phase supply cable from the distribution board to the dimmer rack?
Yes!
Is the rack still connected to the cable?
Yes!
Are the outgoing lighting circuits still connected to the dimmers?
Yes!

Everything is still connected during Insulation testing in this particular dimmer rack. And only this rack failed the insulation test on 500v test with reading of 0.3Mohms.
I will start removing individual connection and run the test until I find the issue.

 

[Pete999]

I should start tracing from the Neutral insulation first? How about the Earth insulation? Thank you!

Are the loads disconnected? sorry already been asked.

 

[markusjames]

Are the loads disconnected?

loads not disconnected.

 

[Pete999]

loads not disconnected.

Disconnect and retest

 

[markusjames]

Disconnect and retest

Will do. Thank you so much!

 

[Lucien Nunes]

At the moment, when you test N-E you are testing the supply cable, all the electronics in the rack, all the outgoing circuits, all the lighting fixtures powered by those circuits, literally the whole system at once. This is not a helpful test (unless it passes!)

Also, the manufacturers may not permit testing just N-E at 500V as this can put the test voltage across the output semiconductors. You must test in accordance with the manufacturers' instructions or you might damage the dimmers.

I can't add any more until you tell the model of the dimmer rack.

 

[markusjames]

At the moment, when you test N-E you are testing the supply cable, all the electronics in the rack, all the outgoing circuits, all the lighting fixtures powered by those circuits, literally the whole system at once. This is not a helpful test (unless it passes!)

Also, the manufacturers may not permit testing just N-E at 500V as this can put the test voltage across the output semiconductors. You must test in accordance with the manufacturers' instructions or you might damage the dimmers.

I can't add any more until you tell the model of the dimmer rack.

We are using
C21 DIMMING SYSTEM
please refer to the photo.
This system supplied by 3 phase power.

 

[goasis]

Why are you testing it??

 

[markusjames]

We are using
C21 DIMMING SYSTEM
please refer to the photo.
This system supplied by 3 phase power.

Why are you testing it??

Annual inspection to check the integrity of the system. We're checking the electrical installation.

 

[dmxtothemax]

it may be that there is an internal neutral to earth jumper in one of the dimer racks ?