Leakage in underground branch circuit

[Mike Harkey]

In a 1200A 3P 120/208V switchboard, with (8) 100A 3P breakers feeding (8) different buildings, with the (8) 1/0 panel feeders underground in galvanized rigid steel conduit. Is there a code requirement, or good practice requirement, for a maximum leakage current in these panel feeder conductors, or a minimum impedance when measured with a 'megger'?

 

[infinity]

What would indicate that there is actually leakage?

 

[John A]

Are we talking Voltage Drop??

 

[Mike Harkey]

What would indicate that there is actually leakage?

There is no indication. What I am looking for is a code standard for what leakage would be acceptable, measured either in amps, or in a megger reading on the insulation.

Are we talking Voltage Drop??

No. voltage drop is not an issue. What I am looking for is a code standard for what leakage would be acceptable, measured either in amps, or in a megger reading on the insulation.

 

[ptonsparky]

There is no indication. What I am looking for is a code standard for what leakage would be acceptable, measured either in amps, or in a megger reading on the insulation.

No. voltage drop is not an issue. What I am looking for is a code standard for what leakage would be acceptable, measured either in amps, or in a megger reading on the insulation.

No such animal.
Read Art 90.1

 

[don_resqcapt19]

I would expect that NETA has some standards, but don't think there any codes that apply

 

[augie47]

When I worked industrial we following this guideline:
A general rule when measuring motor insulation resistance is as follows. 2 megohm or less (bad) 2 to 5 megohm (critical)5 to 10 megohm (suspect) 10 to 50 megohm (good) Above 50 megohm (excellent)

I found comparing readings on a annual basis to be the best guide.

 

[ptonsparky]

Comparing side by side readings is important. 23 checking at 3.5G ohm and one at 50 megohm would certainly be a warning flag for me.

 

[petersonra]

There is no amount of "leakage" that is acceptable, unless you are measuring it at a few milliamps. Keep in mind things like surge suppressors can introduce leakage current.

I would be looking at megohm readings but some conduits might be dry others full of water and that could affect the insulation test readings.

It would be a judgement call IMO. I don't think there is a number that you can use. Now, IF the wires in the same conduit are radically different, that might be meaningful.

 

[jim dungar]

A lot of leakage current comes from capacitance, insulation/resistance testing will not find this current.