Insulation test

[CJW66]

Hi there!
Im on a job where we are installing a 2000 amp 600
/347v 3 ph 4w service. Ontario hydro is installing a Transformer on the grounds and we had to install 6 runs of 5" Pvc in a concrete duct bank, and then have to install 6 parallel runs of 4 #600 kcmil RWU 90(plus ground)about 255 ft long, from the xformer to the Switchgear. We are pulling them in this week. My question is about meggaring (insulation test)the wires before terminating them, after pulling them. We used to use the hand crank, but we just got a fluke 1507 insulation tester. I read the instructions and didnt find them very clear. Havent used a meggar for about 5 years and can barely remember how. Cant remember if you hook one wire of the tester to one #600 and one to ground, or do you put one lead on one #600 and the other lead on the other #600 before hitting test? Or both? I have a few guys on my job and feel kind of embarrassed that i cant remember how to even use the crank if i had it..lol. I remember using the crank and having to discharge the wire to ground when we were done. I know i should use the 1000v scale. I tried googling the meter and such but could really only find info on meggaring appliances and motors. Not just a basic feeder test. Any help would be appreciated. Also, the conduits have water in them. Will that have any effect? Should be ok i think as ive heard of companies submersing whole rolls of wire in water before doing an insulation test...Thanks


Great forum btw. Ive been here many times, but just registered today...

 

[George Stolz]

Always think about what you're trying to test. What are you wanting to know? Is the insulation intact.

Air is an insulator. PVC is an insulator. If the wire is damaged in contact with these there's no way of knowing, and no immediate fault will take place. The water will actually help you in that regard (finding problems). It's unlikely to burn through two insulated conductors rubbing through each other's insulation during a pull, you're worried as to whether the conductors rubbed through and are in contact with the raceway. Test all conductors to a connected EGC and also the earth to verify the insulation is intact. You can test among phases if you like, but it's unlikely to reveal anything.

Good choice on the 1507, IMO.

 

[Smart $]

You test conductor to conductor AND conductor to ground.

Note time, temperature, and humidity on your test report. Also note conductors are submerged in the water in the conduits.

 

[CJW66]

Always think about what you're trying to test. What are you wanting to know? Is the insulation intact.

Air is an insulator. PVC is an insulator. If the wire is damaged in contact with these there's no way of knowing, and no immediate fault will take place. The water will actually help you in that regard (finding problems). It's unlikely to burn through two insulated conductors rubbing through each other's insulation during a pull, you're worried as to whether the conductors rubbed through and are in contact with the raceway. Test all conductors to a connected EGC and also the earth to verify the insulation is intact. You can test among phases if you like, but it's unlikely to reveal anything.

Good choice on the 1507, IMO.

Thanks for your input. The specs on the Job say we have to do this....

 

[CJW66]

You test conductor to conductor AND conductor to ground.

Note time, temperature, and humidity on your test report. Also note conductors are submerged in the water in the conduits.

Perfect. Thanks

 

[big john]

Ground each conductor not under test, that way all possible fault paths are present during the test. It prevents you from having to do a whole bunch of extra tests between each conductor, and also makes sure that capacitive errors are kept to a minimum.

 

[Smart $]

A bit dated but still a good reference...

http://www.biddlemegger.com/biddle/Stitch-new.pdf

 

[CJW66]

Hi there!
Im on a job where we are installing a 2000 amp 600
/347v 3 ph 4w service. Ontario hydro is installing a Transformer on the grounds and we had to install 6 runs of 5" Pvc in a concrete duct bank, and then have to install 6 parallel runs of 4 #600 kcmil RWU 90(plus ground)about 255 ft long, from the xformer to the Switchgear. We are pulling them in this week. My question is about meggaring (insulation test)the wires before terminating them, after pulling them. We used to use the hand crank, but we just got a fluke 1507 insulation tester. I read the instructions and didnt find them very clear. Havent used a meggar for about 5 years and can barely remember how. Cant remember if you hook one wire of the tester to one #600 and one to ground, or do you put one lead on one #600 and the other lead on the other #600 before hitting test? Or both? I have a few guys on my job and feel kind of embarrassed that i cant remember how to even use the crank if i had it..lol. I remember using the crank and having to discharge the wire to ground when we were done. I know i should use the 1000v scale. I tried googling the meter and such but could really only find info on meggaring appliances and motors. Not just a basic feeder test. Any help would be appreciated. Also, the conduits have water in them. Will that have any effect? Should be ok i think as ive heard of companies submersing whole rolls of wire in water before doing an insulation test...Thanks


Great forum btw. Ive been here many times, but just registered today...

So we tested all the wires and 2 have failed in the same conduit. All others passed. We used the fluke and did cable to cable and cable to ground. The 2 that are failing fail cable to cable,and cable to ground(both). After reading another thread in here we tried nipping off a few inches on each end and heating them up with a heat gun. To dry them out. (Never heated up the end that didn't get pulled through the water. Still fail. Brought in our old hand crank meggar and they still fail. Any ideas? Buddy suggested we get someone in to do a highpot test on them? I think we are going to put 120v to them this afternoon and see what happens. Any input would be great! Thanks

 

[RichB]

So we tested all the wires and 2 have failed in the same conduit. All others passed. We used the fluke and did cable to cable and cable to ground. The 2 that are failing fail cable to cable,and cable to ground(both). After reading another thread in here we tried nipping off a few inches on each end and heating them up with a heat gun. To dry them out. (Never heated up the end that didn't get pulled through the water. Still fail. Brought in our old hand crank meggar and they still fail. Any ideas? Buddy suggested we get someone in to do a highpot test on them? I think we are going to put 120v to them this afternoon and see what happens. Any input would be great! Thanks

Pull 2 new cables in
If they failed the megger then they are definitely going to fail a hipot

 

[CJW66]

Pull 2 new cables in
If they failed the megger then they are definitely going to fail a hipot

We inspected the reels of wire before pulling them. They looked fine.
We had to pull a run of 750 kcm aluminum out one time, 400' long because of a failed meggar test. The wire didn't have a mark on it after we pulled it out.
We just put 120v to the wires. 120 v to one wire and neutral to the other. No load of course but it didn't trip the breaker. I'm thinking the wires are wet... I want to cover all bases before it costs us probably 10 grand to replace them. Not easy to pull them out and pull 4 back in. And I don't think it's a good idea to just pull 2 out and pull 2 back in. Could damage the other 2 cables..
Ive had other questionable runs clear themselves after a few days of drying out. Only problem with that is they are sitting in water now.... Be hard to dry them out in an underground conduit.

 

[Tony S]

What is the 120V going to achieve?

I can’t see you have any other option other than replacement. If as you say the specification requires IR testing you’re not going to be popular when it goes bang.

 

[Smart $]

... If as you say the specification requires IR testing you’re not going to be popular when it goes bang.

If part of the specification, the pass/fail criteria should be set in stone so to speak. Unless it can be shown the cable was mishandled and the cause of failure, the cost to replace should be on either the supplier or client.

 

[CJW66]

If part of the specification, the pass/fail criteria should be set in stone so to speak. Unless it can be shown the cable was mishandled and the cause of failure, the cost to replace should be on either the supplier or client.

Yea, I guess we are going to have to pull it out.
That 750 kcmil that I mentioned earlier? 400' long? Like I said, we pulled it out and there wasn't a mark on it. The electrical wholesaler that sold it to us wouldn't replace the wire. They were our #1 supplier that we had dealt with for years and gave them roughly $500,000 per year in sales. We stopped dealing with them, and never went back. They didn't care about losing those sales. And the funny thing is, is that this wholesale supplier(who we just started dealing with), uses the same manufacturer of the wire as the 750. It's going to be a battle.
Also, we are thinking about just pulling one out and using the other one for the neutral. Everything that comes out of the main switchboard now(I neglected to say that we are replacing the service and installing a new electrical room) is all just 3 phase. They have no 347v lighting or anything. ...

Oh, and wouldn't you think the 120v to those two wires that show a dead short trip the breaker?

 

[George Stolz]

Using it as a neutral will mask the problem until it opens and the L-N loads they have added since the original installation start letting out their smoke.

Testing with 120V is probably the least effective test. Due to Ohms Law, it won't even pass an equivalent amount of current as it would when used in the 600V system. The 1507 pointed out the problem, drying out the conductors and whatnot is just deception. Going that route you might as well just make up a number and move on and not waste the time.

Repull the run and inspect what you remove to reuse.

 

[CJW66]

Using it as a neutral will mask the problem until it opens and the L-N loads they have added since the original installation start letting out their smoke.

Testing with 120V is probably the least effective test. Due to Ohms Law, it won't even pass an equivalent amount of current as it would when used in the 600V system. The 1507 pointed out the problem, drying out the conductors and whatnot is just deception. Going that route you might as well just make up a number and move on and not waste the time.

Repull the run and inspect what you remove to reuse.

Thanks for your input. There are 6 #600 neutrals. For the existing service the existing neutrals are only carrying an unbalanced load of 5 amps. They really aren't even using the neutrals. It will be fine I'm sure. The backup generator for the buildings essential service doesn't even have a neutral going to it!! Lol. Nor to the 800 amp emergency panel from the normal power panel. That blew me away right there!

 

[Smart $]

...
Oh, and wouldn't you think the 120v to those two wires that show a dead short trip the breaker?

You didn't say to what degree the conductors failed the test. Are you now saying these two conductors tested at ~0 ohms?

 

[growler]

Oh, and wouldn't you think the 120v to those two wires that show a dead short trip the breaker?

You didn't say to what degree the conductors failed the test. Are you now saying these two conductors tested at ~0 ohms?

I had one like this years ago. They tested good when first installed but then it started to rain for days and the conduits got water in them. Pulled the cable and not a sign of anything bad (short cable and easy to inspect).

If you have a short even a pin hole in the cable you have a problem.

 

[gadfly56]

I had one like this years ago. They tested good when first installed but then it started to rain for days and the conduits got water in them. Pulled the cable and not a sign of anything bad (short cable and easy to inspect).

If you have a short even a pin hole in the cable you have a problem.

I think right there you have suggested the situation. Only thing to do after you pull out the bad actors is to halve them until you find the bad section and hope you eventually have a use for the off-cuts. Or I suppose you could do a corona test if that's economical.

 

[Saturn_Europa]

You didn't say to what degree the conductors failed the test. Are you now saying these two conductors tested at ~0 ohms?

That's a darn good question. Reading a megger can be a little tricky. Especially when it's a new meter.

What was your voltage setting on the 1507? Did the ohms reading start out low then climb up or stay steady?

 

[big john]

Honest question: If you're green at testing, how much would it be worth to you to pay a testing outfit to look at it?

Because were I in your shoes I definitely wouldn't want the thousands of dollars worth of rework to rest on "Well, I guess I'm probably doing this right...."