Hipot testing low voltage cables

[X49]

I have two 600V cables in a facility that are the same size and length. They were hipot tested at 2150V and the results are as follows:

Cable 1: 5000 Megohm, 0.452uA
Cable 2: 100 Megohm, 21.5uA

Are there any rules of thumb for pass/fail? I've read that on Megger tests, the low limit is around 50-100 Megohm. Most of what I've read for hipot testing is for medium or high voltage applications.

I am planning on replacing Cable 2, but would like some data to back up my decision.

Thanks

 

[Zogzog]

ANSI/NETA spec for 600V cable is >100M so you are right there. But the length of the cable will be a factor.

Never heard of anyone hipotting LV cables, not something I would ever recommend (Or any spec I am aware of).

 

[rasevskii]

I do not think hipotting of LV cables is at all advisable, as said. By using 2000+ V, you may have in fact burned something in the terminations. Too late now...? The normal test for such cables would be with a 1000V Megger only. Each conductor to earth with the other two earthed. One minute per each test. If it was all new cable and clean terminations (lifted lugs off any terminal blocks) you might get 100M ohm, or more, but on old cables that were in service a long time, you have to compare with previous tests done before.

My opinion only...others comments welcomed.

rasevskii

 

[collies99]

Fire it up, leakage is negligible, impedance OK.

600V cable application, typicaly 1K insulation class.

Use 500V meggar next time.

 

[ausphil]

If you are planning to replace cable 2 based on the IR and leakage current readings you have shown, then you have more money than you need.

We recognise that older cables do have lower IR than brand new ones, and also the type of cable insulation (paper, XLPE, EPR etc) will determine whether you have a problem or not.

I would be happy to return this cable to service and not come back to it for many years. It is only a 600V cable anyhow.

We will return cables that have IR values as low as 100kOhm, knowing that it will more than likley hold for a reasonable period of time, to allow us to plan to replace them.

If you are looking to replace the cable based on other reasons, then that is fair enough, but if you are going to justify the replacement on an IR value, then it will probably be questioned by someone with even just a little knowledge.

ausphil

 

[X49]

Thanks for the advise guys. I've looked at the NETA MTS standard and it does recommend a minimum 100 megohm (though I realize this is a pretty stringent requirement)

The cable that is reading 100 megohm has been physically damaged, which is why we tested it (and the other identical cable for reference). It is only a year old. The cable jacket has been pretty badly damaged and since it's reading 50x lower than the other cable I'm assuming that the insulation has been somewhat comprimised.

I am still planning on recommending replacement since the replacement cost is not prohibitive.

 

[ausphil]

Is repair not an option?

ausphil