Earth to Nuetral 2 ohm with Multimeter cable disconected form switch board.

[MarkBarrie]

Earth to Neutral 2 ohm with Multimeter on alighting cct. The cable disconnected from the switchboard.
I am new here and appreciate everyone looking at this post.
I come from an Industrial Electrical background and would like advice on fault finding.
My house has 1 lighting RCD. There seems to be 3 different TPS 1mm 3 core (A, N and E)
I removed each cable and Isolated it to one of the cables. I disconnected A,N,E of this cable from the switchboard. My Megger has an Ohms setting and measures A, N to E individually. It measures 2 ohms between N and Earth.
The following is what I believe is connected to this circuit.
1) Domestic exhaust fans in bathrooms.
2 Outside lights. These are either full insulated spotlights Earth with sensors (these have led ballast) earth not connected to fitting) or batton holders with LED or fluorescent globes plugged into them.
3) Ceiling fans with speed control light switches.
4) LED downlights. These are the type that takes 240V straight into the light. (Not external transformers.)

The cable is an older cable with the earth in the TPS not being insulated.

I have started disconnecting external floodlights and still have 2 ohms.

I would appreciate your feedback on this issue?
1) what is the most likely cause of the issue?
2) What is the best way to efficiently find the issue?
3) What would you disconnect before doing an insulation resistance test?

 

[Geoff1946]

I think you are saying that you have a neutral to earth fault and want advice on tracing it (?)
Separate the three cables you refer to. Hopefully the fault will then be on only one of them.
If you can physically trace the cable do so. If not determine what loads its feeding by continuity test with a flying lead.
Dismantle and inspect all connections testing each until you find fault.
It's more likely on something which uses the earth than a double insulated one. I would look first at the fan. If it's not one of the loads or connection points then its a cable fault. Have you done any work recently, putting in nails or screws?

 

[ProDave]

At 2 ohms you should be able to calculate roughly how far from the point of measurement the short is, which might help a bit.

This is a UK forum so our wiring practices and terminology will vary to what you are used to so there might be some confusion.

It is in most cases a case of completely disconnect the cable at each light fitting or light switch (depending if it is loop at light or loop at switch) until you find the fault. Best case you will find a fault at a junction, worst case you will find a length of cable with both ends disconnected that still has the short = nail or screw through cable.

 

[MarkBarrie]

I think you are saying that you have a neutral to earth fault and want advice on tracing it (?)
Separate the three cables you refer to. Hopefully the fault will then be on only one of them.
If you can physically trace the cable do so. If not determine what loads its feeding by continuity test with a flying lead.
Dismantle and inspect all connections testing each until you find fault.
It's more likely on something which uses the earth than a double insulated one. I would look first at the fan. If it's not one of the loads or connection points then its a cable fault. Have you done any work recently, putting in nails or screws?

Geoff,
Thank you for your reply. I have separated the cables in the switchboard. Remove the guilty cable for all connections in the switchboard. The test I did was a continuity test which came up as 2 ohms between N and E. No changes were made to the house for years.
I forgot to mention. I think some of the old light and fan switches, switch to Neutral. Unlike the way I was taught which was a 2 core switch wire to the light fitting and switch.