Insulation Resistance . Please help I never get good reading

[JohnW2]

Well, we hope he disconnected the L & N busbars from the incoming supply by opening the main switch.

Quite - my very point ... and, as I said, assuming that was done, the fact that N&E are connected upstream of the CU (at cutout, generator or wherever), as mentioned by TTC, is not, in itself, relevant to IR testing.

On another point in relation to testing with MCBs connected, can we be sure that no modern MCBs contain any 'electronics' which could affect IR measurements (or even make them susceptible to damage from IR testing)?

Kind Regards, John.

 

[studentspark]

Here's my thinking of it.

If all the neutrals are together, it is in effect one cable.

If I test that cable to live, but only through one MCB then the installation resistance between live and the other neutrals will be high as they are not the same circuit and not even the same cable.

But... I guess the IR could be pulled down as the "length of the neutral has effectively increased by a large amount

 

[riveralt]

Earlier you asked why you are always getting a poor IR reading.. you appear to have started jumping to conclusions without conducting the test properly...

The correct procedure is to remove the L&N wires from the protective device and neutral bar, and test between L&N, L&E, N&E.
Repeat for each and every circuit.

Have you done that and what was the result?
If you still get the same result - then your meter could be faulty, the way you are testing could be faulty or you have a problem on the circuit.
If its the latter issue, break the circuit down and test for IR along individual legs.

 

[RF Lighting]

On another point in relation to testing with MCBs connected, can we be sure that no modern MCBs contain any 'electronics' which could affect IR measurements (or even make them susceptible to damage from IR testing)?

Yes we can.