Storage heater testing

[Spark123]

Yep, ignore doing L-N insulation readings for now as the load will cause it to read closed circuit.
An earth leak caused by a L-E fault is more likely to be the cause and will trip an RCD.
With the switches all closed (except the main switch on the CU), the thermostats turned up so they are closed, what are the L-E insulation resistance readings?

 

[ricicle]

I IR'd them from the fuseboard, firstly with the switch off and they were all clear as a whistle, then switches on but thermostats on low, if I turned them up readings were 0000mohms,

It sounds as if you are a little confused with the testing. If you are testing them at the CU with the themostats low then there is a possibility you are not testing the elements, just the installation wiring.
If the IR is showing a dead short when the stats are turned up then you are probably testing through the element back to the N and then E. Are you disconnecting any Neutrals. I hope you are switching off the main switch on the storage heater CU even if the off-peak is not energised!

 

[burntwire]

Yep, im turning off the main switch as im never trusting things out of my control, I probably am a bit confused as Ive never tested heaters before, I didnt disconnect any neutrals, but by turning the thermostats to low Im surely testing the wiring up to the thermostat ?

There is a dead short when the thermostat is turned to high.

If I understand that a closed switch means on ( ive never heard this before) then Im sure they were the same as above altough I didnt write them down,

 

[Spark123]

You'll end up with an overall L-E resistance (including N-E) if you do a L-E with the switches and thermostats closed as the voltage from the test will feed through the elements back to the neutral bar in the CU back via other elements to the other lives. The element resistances are relatively low compared to the required insulation resistance hence only effect the result very slightly.
This reading should be up into Mega Ohms.
Worth checking MCB output in turn.