Insulation resistance query

[Welsh_sparky_21]

Was testing a 3 phase DB for storage heating. While testing I noticed I was getting continuity between 2 of the circuits, which were on separate phases. Each storage heater has its own 20A radial, and when doing an insulation resistance test between 2 of the circuits I get a reading of 0.00 ohms. I only get this reading between the 2 live cables, all other conductors are clear. Very strange reading to get, what are the chances of the 2 cables coming into contact and only the lives touching each other, or is there something I am missing?

 

[westward10]

Were the neutral conductors connected to the neutral bar.

 

[James]

i suspect that the heaters are switched on, you will continuity through the following links
heater 1 live to heater 1 N
heater 1 N to heater 2 N (common link)
heater 2 N to heater 2 live

therefore, continuity between heater 1 live and heater 2 live

 

[Welsh_sparky_21]

Were the neutral conductors connected to the neutral bar.

Yeah, I just disconnected both live conductors. The neutrals would have been still connected

 

[westward10]

So draw out your two circuits. Two resistive elements, a neutral from each to the neutral bar and the two live ends. You have a complete circuit.

 

[Welsh_sparky_21]

So draw out your two circuits. Two resistive elements, a neutral from each to the neutral bar and the two live ends. You have a complete circuit.

But why only those 2 circuits? Why is this not the case with the other circuits, these were the only 2 circuits I had continuity between the live conductors

 

[James]

But why only those 2 circuits? Why is this not the case with the other circuits, these were the only 2 circuits I had continuity between the live conductors

thermostats, switches, time clocks? any of them in circuit could prevent you from getting continuity through the circuit.
as westward suggests, draw out the circuit on a piece of paper and all will become apparent.

 

[Welsh_sparky_21]

thermostats, switches, time clocks? any of them in circuit could prevent you from getting continuity through the circuit.
as westward suggests, draw out the circuit on a piece of paper and all will become apparent.

I understand why you would get continuity if the neutrals are still connected, through the elements. Just confused me as to why it was just they 2 circuits and none of the other 5

 

[westward10]

As above were they on and in circuit.

 

[Welsh_sparky_21]

As above were they on and in circuit.

As above were they on and in circuit.

All heaters were switched on

 

[Welsh_sparky_21]

All heaters were switched on

Off sorry

 

[Welsh_sparky_21]

As above were they on and in circuit.

I’m going back tomorrow, I’ll disconnect both cables completely at both the mcb/neutral bar and the DP switch and re test and see what result I get

 

[westward10]

As I said draw it out put some switches in then you can see the scenario, it is the best way to make it clear.

 

[Welsh_sparky_21]

As I said draw it out put some switches in then you can see the scenario, it is the best way to make it clear.

Will do, thanks for the help!