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Posted By Topic: N-E continuity with MEN link pulled

OctaneOutlaw
Nov 25 2019 11:16

Sometimes whilst testing I find N-E continuity with the MEN pulled, a lot of the times I've found it stops once the incoming neutral is disconnected

Is there something I'm missing?

Is it something I have to remedy or as long as the circuits I've worked on with there N disconnected is fine do I just walk away because that's how it is?
   

AlecK
Nov 25 2019 12:17

It's all in the name of the system used in NZ for distribution: MEN meaning multiple earthed neutral.

The N of each HV / LV tx is earthed at origin, and at every installation, plus sometimes at intervals between these places. This keeps the distribution N at approximately zero v to mas of earth.

Its only natural that you'll get readings showing some sort of continuity between your installation system and mains N, because of all these connections-in parallel.


   

pluto
Nov 25 2019 12:18

The incoming supply is an TN-C-S supply (the equal of the AS/NZS 3000 MEN system) which is earthed at the supply transformer and at all electrical installations connected to the lines comapany distribution system neutral conductor.

The lines co. distribution system neutral conductor will be at approx 10 ohms to earth, or ought to be near this figure, so when the mains neutral is connected is provides a earth referanced connect in parellel with the main earth electrode and the HWC earth, if connected by metallic pipes and in contact with the mass of earth.
   

OctaneOutlaw
Nov 25 2019 12:28

Ah, of course, feel stupid for asking this one haha

Thank you

Is it common practice to pull the incoming neutral during such tests?
   

DougP
Nov 25 2019 13:19

Which test?

N-E IR test?

You should have the circuit N disconnected for that test (either removing the conductor, or opening the RCD if fitted). The main incoming N connected and the MEN link must be left in place for the test.


   

OctaneOutlaw
Nov 25 2019 15:54

Insulation resistance testing between P N (Joined together) and earth
   

OctaneOutlaw
Nov 25 2019 16:27

I would normally disconnect the circuit N under question and link it with the P of the subcircuit then test between this and E

Due to the board being messy rather than disconnecting the N, I removed the MEN thinking it would give the same effect of disconnecting the N from E
   

DougP
Nov 25 2019 19:38

Have you looked at 3017?
   

OctaneOutlaw
Nov 25 2019 22:08

Yeah, I have a copy, that's where I learnt to link A-N and test to earth