insulation resistance testing

[AKsparky1]

I am looking for insulation resistance testing standards for power conductors. At my job we build pre-manufactured wood frame motels and man camps here in Alaska and we mostly install MC cable THHN sometimes XHHW 600v rated and we test all runs of cable before conducting a power test. We use 2.2 G ohms as a standard but sometimes cannot get that high of a reading do to the cable being encased in spray foam. My question is what is the minimum standard for this wire? I believe it is much lower then the 2.2 G ohms but where can I find the formal standard? I checked IEEE 43-1974 but that is for windings for machinery I believe.

 

[GoldDigger]

I am looking for insulation resistance testing standards for power conductors. At my job we build pre-manufactured wood frame motels and man camps here in Alaska and we mostly install MC cable THHN sometimes XHHW 600v rated and we test all runs of cable before conducting a power test. We use 2.2 G ohms as a standard but sometimes cannot get that high of a reading do to the cable being encased in spray foam. My question is what is the minimum standard for this wire? I believe it is much lower then the 2.2 G ohms but where can I find the formal standard? I checked IEEE 43-1974 but that is for windings for machinery I believe.

Unless the chemicals in the spray foam are degrading the conductor insulation, just encasing the MC in spray foam should not change the measured insulation resistance. And if the foam is indeed incompatible with the wire insulation you have bigger problems that just setting your test standard value.
In theory, nothing which is done outside the grounded metal sheath of the MC should affect resistance measurements inside it. Or are you seeing moisture accumulating inside the MC? That should not affect the DC resistance, but might increase the capacitive current if you test with AC.

 

[cadpoint]

Look up " A Stitch in Time " is gives a good overview of manually testing wires.

 

[Sierrasparky]

Unless the chemicals in the spray foam are degrading the conductor insulation, just encasing the MC in spray foam should not change the measured insulation resistance. And if the foam is indeed incompatible with the wire insulation you have bigger problems that just setting your test standard value.
In theory, nothing which is done outside the grounded metal sheath of the MC should affect resistance measurements inside it. Or are you seeing moisture accumulating inside the MC? That should not affect the DC resistance, but might increase the capacitive current if you test with AC.

Good pioint I missed that.