Fault on Ring final circuit

[pc1966]

L+N -CPC 29.1

Bemused. Will break the circuit at a socket now.

It looks like the pump you just disconnected. Test it separately and see if low IR to E, most likely water in somewhere!

 

[pc1966]

While it is possible to get a L-N fault that does not involve the CPC, it is hard to do with T&E cable due to its physical layout (CPC in the middle) and at accessories it is usually a fault to the back-box (cable nipped by screw sort of thing, missing grommet allowing cable-box cut, etc)

Do a continuity test L-N and see if it is low enough to trip the MCB side (so under 5-ish ohms) or it is tens of ohms or more like a small-medium motor waiting to start.

 

[AJB Temple]

This is so confusing! You guys are so helpful.

Right, I have connected CPCs back to the earth bar in CU. Put both live and both neutral from the ring into a 5 way wago, with a new wire out from it to test. Put green lead from Megger on the CU earth bar and red onto the lead from the wago connecting ring together. Insulation resistance test on that gives 35.8 M Ohms.

 

[pc1966]

Right, I have connected CPCs back to the earth bar in CU. Put both live and both neutral from the ring into a 5 way wago, with a new wire out from it to test. Put green lead from Megger on the CU earth bar and red onto the lead from the wago connecting ring together. Insulation resistance test on that gives 35.8 M Ohms.

That is good.

As a general rule, you always do IR testing with the CPCs connected to the MET (earth bar) so a fault to external metal / true Earth (e.g. screw through cable) is seen even if it is not touching the CPC conductors.

 

[pc1966]

Now check the pump!

 

[AJB Temple]

Right. Checking the pump is not so easy as the inspection hatch is a two man lift, as it is an inspection cover filled in with stone. However, I have reconnected the ring main back into the CU temporarily using Wagos and it has not tripped so far.

 

[pc1966]

Right. Checking the pump is not so easy as the inspection hatch is a two man lift, as it is an inspection cover filled in with stone.

Can't you IR test at its plug?

However, I have reconnected the ring main back into the CU temporarily using Wagos and it has not tripped so far.

That is encouraging!

 

[timhoward]

Right. Checking the pump is not so easy as the inspection hatch is a two man lift, as it is an inspection cover filled in with stone.

Do a quick L-E and N-E test using the clips on plug pins.

 

[davesparks]

No need for line to neutral IR tests. As it stands those readings are above minimum limits.

They aren't, post 26 states line to neutral is 0.01Mohms

 

[pc1966]

They aren't, post 26 states line to neutral is 0.01Mohms

I think we all suspect that is not really the cable alone, and something is still connected. But the L/N to E are now good with the pump unplugged, so the culprit would now appear to be cornered awaiting the electron police...