I know the "N" stands for Nylon.
By reading articles and other code sections i assume if the nylon is broken or damaged then the THHN conductor can not be used in a submerged environment. Another words if you install a THHN/THWN under ground the nylon covering can't be damaged.

I searched the Southwire PDF file on THHN/THWN and the white book but could not find anyhting specific to the nylon jacket.

or the nylon covering is strictly for easy pulling?

Sometimes THHN does get scratched if you are not careful. I would not scrap the pull for this minor problem, unless it was bad. That rarely happens.
I guess the nylon thermoplastic covering serves both purposes.

The nylon is definitely for "scratch resistance". It has no impact on the "water resistance" although it may come into play for gasoline.

In the last year or so, in the IAEI magazine, UL stated that the nylon jacket is there as an aid to pulling the conductor in conduit. JBD is on the right track, damage to the jacket is of no consequence unless the conductor will be immersed in oil or gasoline.

Tom,
I will contact UL today and i will bring this issue at the IAEI meeting.

I will reply with what what i find.

I received the following from Jeff Posey an application engineer from Southwire:


"Damaged Nylon on THHN cable
The wrinkling and small tears in the nylon jacket should have no effect on the insulation values of the cable. The nylon serves three functions in the role of the cable, none having an effect on the electrical integrity of the cable:

The first function of the nylon jacket is to provide mechanical protection to the PVC insulation during installation. The nylon jacket protects the PVC insulation from the hazards and rigors associated with pulling cables in conduits and cable trays. Because it is such a thin layer, it is common for the nylon jacket to tear during pulling. Many consider it to be a sacrificial layer. Most importantly, however, since the nylon does not serve a purpose in the electrical performance of the cable, one should not expect to experience any electrical problems with the cable as long as the PVC insulation is not damaged during installation. If the PVC insulation is damaged and the cable is installed in a wet environment, then the chances of failure for the cable increase. Adherence of proper cable installation techniques and sufficient lubrication should minimize the potential for damage to the cable.

The second function of the nylon jacket is to provide gasoline and oil resistance for the PVC insulation. Operating the cable where it may be subject to these conditions could present problems. The end solution for these problems would be replacement of the cable. If these conditions are not present, again, there should not be any anticipated problems.

The third and final function of the nylon jacket is to provide protection to the cable from Ultraviolet Light Exposure. Special inhibitors are added to the nylon to permit the cable to be used in applications where exposed to sunlight. This feature, however, only applies to those Southwire constructions marked “Sunlight Resistant”. Small tears in the nylon should not jeopardize the integrity of the cable in such applications."

I thought Southwire was the "No-Lube" wire.

I got the same story from Southwire a few years ago, but they still didn't answer my question.
If the nylon is to protect the insulation, and it gets nicked during installation at the first bend where it enters the conduit, what protects the insulation during the rest of the pull?
All I got every time I asked that was the same parrot response that they gave the first time. I don't trust the stuff for just that reason. I spec a lot of XHHW-2 for underground work and the large feeders. I've had some very bad experiences with nylon stripping off as soon as the wire comes off the reel and into the end of the conduit run...even to the point where runs had to be pulled out and replaced because the underlying insulation was damaged further on down the conduit run.

This is comment from UL. principle engineer wire and cable.

1. The nylon is their for mechanical protection as well as oil and gasoline resistance.
2. If the nylon jacket has tears, the oil and gasoline performance of the wire is compromised.

When it comes to feeders all I've ever worked with is XHHW-2 with aluminum conductors or much more rarely - due to cost - THWN-2 and copper conductors.

In no circumstance did I ever experience meaningful damage to the nylon jacket.

It was the smaller branch conductors rated THHN/THWN-2/MTW that suffered. Poor pulling geometry from time to time scraped the jacket in a nasty manner.

Normally I stopped the pull the minute this happened. Typically the damaged wire was rejected and a fresh pull was started. We're talking #10 for home-runs, typically.

My logic was: no way can the company make money pulling warranty replacements AFTER the store is up and operational.

So it really gets down to how much your reputation means to you -- how much you can afford for warranty call-backs.

As for myself, I eliminate the problem by not scoring the conductors -- no matter how much effort that takes.

A few years ago, Southwire also told me the same thing, but still did not answer my question.What will protect the insulation during the remainder of the pull if the nylon is damaged during installation at the first bend where it enters the conduit? The parrots always gave me the same answer when I asked them that the first time. Those reasons alone make me distrust the stuff. The large feeders and underground work that I specify often require XHHW-2. In the past, I've encountered nylon separating right away as soon as the wire is unrolled and entered the conduit. Upon further inspection, the underlying insulation had been damaged further down the conduit run and had to be removed and replaced.

Who can tell what happens to any wire in the middle of a pull?

Don’t let your imagination get carried away. Use plenty of water based lube - them megger the run after the pull if you’re concerned. Test instruments don’t lie.

Reno....

A blast from the past. How are ya bud??