Lightning damage Insulation resistance test

[eebbob]

For making a spot IR test (good/not good) on circuits in a residence, wouldn't it be OK for the general purpose circuits to disconnect the lighting fixtures and leave the wall outlets (with no load) and closed light switches in place? If this combination did not test above about 1 megohm, then the outlets and the switches would need to be pulled and each cable run tested separately. Thanks

 

[IRstuff]

I'm unclear as to what you're trying to do. Getting to a zero-load condition on each and every circuit in a house is non-trivial. I've got something like 20 circuits, and many of them have built-ins wired to them, and others have possibly unknown or unaccounted for loads.

TTFN

FAQ731-376

 

[eebbob]

Yes, I know getting to zero load on some circuits could be an issue. I want to make insulation resistance measurements using a megohmmeter on those circuits that I am confident in getting to zero load, which will be almost all of them. My question is, can I meg thru outlets and light switches or must I isolate them too.

 

[VEBill]

Obviously, disconnect from the power source. Beware illuminated switches with the built-in neon bulbs. Remove any dimmers or fancy programmable switches. Consider 3-way switches (test twice or more). If you're using a hi-pot type tester, keep the voltage reasonable (600 peak?). Note, I'm not familiar with the applicable regulations (if any). But it seems to make sense that entire circuits could be tested at once.

Years ago, we had a nearby lightning strike. It tripped the main 200A breaker. After the storm passed, I reapplied main power and found one 15A circuit breaker tripped. When I turned that back on, there was a flash and puff of smoke from the outlet box. Called the Fire Dept to make sure there wasn't any fire. Later found that the insulation was damaged where the cable entered the box.