pre consumer unit change

[Guitarist]

guitarist, what is the rational behind the IR @ 250v ? i thought, apart from SELV, it was used before a 500v test as a way to check if you've missed removing one of the loads.

also, when would the L and N to E insulation test be used? is the pass for this test still 1MΩ, check if below 2MΩ? i got told that L and N to E should be done when there are loads or sensitive equipment that cannot be removed. If this acceptable, do people not bother with removing the loads for the full IR test (L-N, L-E, N-E) and just do this instead?

Exactly what you say. 250v test just a quicky to see if there is anything obvious before agreeing to change the CU, without the risk of damaging anything.