Nitrogen Purging of Conductors

[iwire]

OK, I guess I wasnt much help there,

Neither was I.

How confident are you in the capabilities of the company or person that did the testing?

I know the Foreman on the job is no rookie, but I have no idea who did the testing. I do know that many of the jobs this Foreman runs requires mega testing and reports generated so the process is certainly not new to him.

 

[Pierre C Belarge]

I know this is not your fault, and what I am about to write is not normal procedures.

It would have been interesting to see the results of a megger test on the conductors before pulling them in, and then after pulling them in. This would let one know if the process of installing the conductors created the issue or if the conductors themselves are the issue from the manufacturer.

 

[don_resqcapt19]

It would have been interesting to see the results of a megger test on the conductors before pulling them in, and then after pulling them in. This would let one know if the process of installing the conductors created the issue or if the conductors themselves are the issue from the manufacturer.

If this is single conductor cable, the test on the spool will not show bad with a megger even if it has bare spots. There has to be a conductive path. Where would that be with the conductor on the spool?

 

[zog]

If this is single conductor cable, the test on the spool will not show bad with a megger even if it has bare spots. There has to be a conductive path. Where would that be with the conductor on the spool?

Unless it is MV cable, that always is tested on the spool and after installation before being energized.

 

[drbond24]

The problem with water inside the cable is that it allows a conductive path around the insulation. The insulation is rated to keep water out of the cable. If there is already water in the cable it must be removed or all bets are off.

When a UL insulation test is performed, the entire length of cable to be tested is submerged in water so that the OUTSIDE of the cable is completely under. There is still no water INSIDE the cable at this point.

There is only one place in the entire manufacturing process where water can enter the conductor and the extruder operator would have to be asleep for that to happen. It is possible, but unlikely.

Now that I have given my opinion, I must be honest. I work for Service Wire Company and the person telling you to Nitrogen purge the cable is my boss. :grin: :grin: We do replace cable if we messed it up; we sent a free reel of 1000 feet of 400 MCM to Alaska earlier this week because the first one had a poor guide job. In this case however I can tell you that there is no way to prove when the water entered the cable other than what I've already said. It is highly unlikely that it was during manufacturing. Most likely is that it occured in transit or the reel(s) were improperly stored at the supply house before you received them. All cable that leaves our facility is tested first so bad insulation can't get anywhere near the door without setting off an alarm.

My advice would be to file this in the 'stuff happens' catergory and use the nitrogen purge, but then again I am obviously biased. :smile:

 

[LarryFine]

Figuring that the problem is with the length of conductor inside the conduit, and not at the terminations:

The insulation is a plastic tube. It shouldn't matter if the tube is filled with water or copper. The only way current (not reactive) can pass through the tube wall is through pores in the plastic.

Poor insulation performance requires a conductive pathway between the inside and the outside of the tube, doesn't it? Water inside the insulation shouldn't matter as long as it has no physical effect on the material.

What if the insulation contained water inside it, and it was passing through a metallic medium on the outside? Wouldn't the same things matter? No pathway, no current?

 

[drbond24]

Figuring that the problem is with the length of conductor inside the conduit, and not at the terminations:

The insulation is a plastic tube. It shouldn't matter if the tube is filled with water or copper. The only way current (not reactive) can pass through the tube wall is through pores in the plastic.

Poor insulation performance requires a conductive pathway between the inside and the outside of the tube, doesn't it? Water inside the insulation shouldn't matter as long as it has no physical effect on the material.

What if the insulation contained water inside it, and it was passing through a metallic medium on the outside? Wouldn't the same things matter? No pathway, no current?

What I'm saying is that with water inside the insulation, there is a path for the current that shouldn't be there. It doesn't have to go through the insulation anymore, it can go around. When you connect the leads of the meggar to the conductor and the insulation, the water is a short between them. You aren't testing the insulation at all, you're measuring the insulation resistance of the water which is going to be waaaaaaaaaaaay lower than the insulation. There is water in the copper and there is water on the inside wall of the insulation and it is the same water. You can connect your leads to the copper and the insulation but all you're getting is the water.

 

[HighWirey]

Has anyone done it or know about it?
I was asked to find out about it.
Apparently a new conductor Meged out poorly. The conductor manufacturer has suggested the conductor is wet and has recommended that the conductor have a 15 to 20 PSI supply of Nitrogen or Dry air applied at one end then let run 8 hours after all signs of moisture are gone.
Thanks in advance, Bob

Bob,

Some remedial repairs may work, some may not. Three things are sure, all of those remediation schemes are costly and may be temporary, you will be responsible until your warranty is satisfied, and your customer will always wonder about your competenance as a contractor.

Remove and replace that bad run now. Never thought I would ever proffer this advice, but you only have to experience a bad pull one time. How much does it cost to replace that run today versus a week prior to warranty expiration? Priceless . . .

I realize I did not address your OP, but you get my drift, sir.

Best Wishes Everyone

 

[iwire]

When you connect the leads of the meggar to the conductor and the insulation, the water is a short between them.

But that s not what we are doing, and I don't see how that would work.

I believe the tests where copper to copper and copper to ground.

But, I really appreciate your responses. :smile:

 

[drbond24]

I realize that this has strayed completely away from your OP, but would you mind providing the length of the run, the type of meter that was used and the resistance readings that were taken? That way, I can be the dork I was born to be and do some math.

 

[iwire]

would you mind providing the length of the run, the type of meter that was used and the resistance readings that were taken?

I would not mind at all :smile: , but I was not involved and can not answer those questions.

Since my original post I have talked to someone that was there and they told me some of the readings......I think we will be replacing the conductors.

 

[drbond24]

I would not mind at all :smile: , but I was not involved and can not answer those questions.

Since my original post I have talked to someone that was there and they told me some of the readings......I think we will be replacing the conductors.

:grin: Oh well, I tried. :grin:

 

[iwire]

:grin: Oh well, I tried. :grin:

Thank you.

And thank you to all that have chimed in, if anyone has more info please feel free to jump in. :smile:

 

[rcwilson]

Water in Cable

Water in Cable

Several posts have stated that there is no way for water to get in the cable except through the insualtion. I have seen cut ends of cable get dropped into water-filled manholes allowing water to enter the end of the cable. On another project, the temporary cable end seal got damaged. When the 4 feet of snow melted, water flooded the area where the cable was temporarily fastened. In both cases water entered the ends of the cable under the jacket, not through the jacket or through the insualtion.

Could the cable have been left in the weather with a bare end allowing water to get inside?

 

[drbond24]

I believe the tests where copper to copper and copper to ground.

Ok, I am an engineer sitting at my desk and not a technician actually performing these tests, but don't you need to connect the leads to the copper and insulation of only one cable to be testing the insulation? I have attached a document that shows how to test insulation among other things.

Type this into Google: extech model 380375 manual

and look at the bottom of page #6 on the first hit you'll get from the search.

 

[iwire]

Several posts have stated that there is no way for water to get in the cable except through the insulation.

I don't think that is what they are saying.

I believe the consensus is that if the cable was full of water and the insulation was intact that it would still test fine. :smile:

The only way it is testing bad is because the insulation is compromised somehow.

There is no question water can wick into the cable from an open end but it takes a hole in the insulation to make a bad test.

 

[drbond24]

The consensus is that global warming is a threat to planet earth, but that is a load of crap too.

Seriously though, and with all due respect, you are wrong. I am not saying that there is no possibility that the insulation is damaged. It has happened before. However, water in the cable ruins the insulation test, period. How can a bunch of electricians all of a sudden have no problem with water being all over the electrical equipment? Isn't that something that you would usually avoid?

 

[iwire]

Seriously though, and with all due respect, you are wrong.

Cool. :grin:

I am not saying that is not possible, but I don't think so on this thread. :smile:

How can a bunch of electricians all of a sudden have no problem with water being all over the electrical equipment?

Because if the insulation is intact then all the water is doing is becoming part of the copper conductor. Like Don and Larry have explained.

Picture the wire in the metal raceway, one lead of the mega is connected to that metal raceway, the other lead is connected to the copper conductor, the only path for that circuit is out through the insulation.

See figures 13 and 14 for representation of how we are testing.

For cables 600 volts and under I don't think there is every a time where we would measure with one lead on the insulation and one lead on the copper.

 

[drbond24]

I'm going to take this theory and run with it. Before long we'll be selling XHHW tubes full of water instead of copper. It'll be way cheaper and lighter and you all apparently think it will work the same. We just need to figure out how to terminate it. :grin: :grin:

 

[iwire]

I'm going to take this theory and run with it. Before long we'll be selling XHHW tubes full of water instead of copper. It'll be way cheaper and lighter and you all apparently think it will work the same. We just need to figure out how to terminate it. :grin: :grin:

Kidding aside did you bother to take a look at the link I posted?

In the testing method I pointed out can you explain how water inside the insulltion change the result?