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Insulation resistance with loads connectedWho unplugs the client's equipment?

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Insulation resistance

An insulation resistance tester, reading in megohms — millions of ohms. The default test voltage is 500 V DC.

TestVoltage
Live conductors (line and neutral linked) to earth500 V DC
Between live conductors500 V DC
Where sensitive equipment cannot be removed — live conductors linked, to earth250 V DC
✋The client removes the loads, not you. Move their equipment and break it and you are liable for it. Removing loads is part of the extent and limitations agreement — agreed before you start.

What counts as sensitive

Anything with electronics in it. 500 V DC through it will not do it any good.

SPDsRCDs and RCBOs
AFDDsUSB socket outlets
Neons in FCUs and cooker switchesDimmer switches
Voltage-operated earth leakage circuit breakers — obsolete, but still found on old installations
SituationBest approach
New installation, not yet terminatedTest on the cable itself at the full 500 V, before anything is connected
Device at the boardPull the conductors out of the device and test on the cable
Something sensitive downstream that cannot come outDrop to 250 V, or drop the faceplate and link the conductors in a connector block to bypass the electronics
AFDDs are increasingly combined units — AFDD, RCD and overcurrent protection in one module. There is nothing to unplug, so pulling the conductors and testing the cable is the only option.
Test circuit by circuit as you install. Continuity then insulation resistance on each circuit before moving to the next, rather than wiring the whole board and then pulling every conductor back out.

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