THHN- NYLON JACKET

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mstrlucky74

Senior Member
Location
NJ
Was watching a MH video and he mentioned the that nylon jacket was not part of the insulation but he was not 100% but was awaiting confirmation. He talked about a story were guys in N. Dakatp were pulling wire and it was so cold the nylon jacket cracked and broke off but the wire was still good. It's just to make the wire pull easier. Is this tue? Thanks
 

kwired

Electron manager
Location
NE Nebraska
Inspectors here will reject "skinned" nylon jacket in areas subjected to gasoline or oil, supposedly the nylon jacket is the component that gives it a gasoline and oil resistant rating.
 

kwired

Electron manager
Location
NE Nebraska
It is the sealing component
If you have ever worked on small engines non metallic parts in carburetors are nylon and not PVC, as nylon is resistant to gasoline but petroleum based plastics are not. With THHN the nylon is over top of a petroleum based thermoplastic. Why not use an all nylon based insulation instead? I don't know. Perhaps the insulation quality of nylon is less superior, more expensive or maybe other properties come into play.
 

Gregg Harris

Senior Member
Location
Virginia
Occupation
Electrical,HVAC, Technical Trainer
If you have ever worked on small engines non metallic parts in carburetors are nylon and not PVC, as nylon is resistant to gasoline but petroleum based plastics are not. With THHN the nylon is over top of a petroleum based thermoplastic. Why not use an all nylon based insulation instead? I don't know. Perhaps the insulation quality of nylon is less superior, more expensive or maybe other properties come into play.


posssibly flexabillity and temperature
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Here is an excerpt from an old IAEI meeting, Dave is Dave Mercier of Southwire.

When Gil visited us previously, he made a splash by noting that the transparent nylon covering THHN/THWN, while arguably making them sexy compared to THW, is not required to maintain the conductor's dielectric properties. Therefore, if in the course of installation the nylon suffers the odd nick, or unsightly run, or even is scraped off, the conductor is fine so long as the insulation underneath remains intact. Learning this much, we had to have Dave over for more of the story.

Unless conductors are exposed to gasoline or oil, or submerged for an extended period we're talking many months--the nylon covering offers strictly a mechanical protection, Dave explained, with the underlying PVC supplying the dielectric properties as Gil had told us. The nylon actually is stripped away for the UL acceptance test. Therefore, if the nylon is scraped off, but the plastic underneath is intact, an appropriate response usually is "Good; it's done its job," and a green tag.

It's not just the nylon covering on THHN/THWN, we learned, but the sheaths on cable assemblies also often are optional. A cable installer nicked the sheath of a nonmetallic cable installed in a dry indoor location, and responded in a curious way: he turned the cable so the nick faced toward the wall. Not a bad response, Dave opined (while not wholeheartedly endorsing); this way, people glancing at it in passing wouldn't be unnecessarily concerned.
You may detect from this that Dave is quite an engaging speaker; moreover he's one with 19 years' product and Code experience under his belt to give plenty of clout to the information.

Damage is not necessarily limited solely to cable sheaths, of course. If a cable appears damaged, Dave recommends cutting a window in the sheath so you can examine the conductor insulation beneath. If that's good, you can "reinstall the window."

What should you do when you do want to, or need to, repair a cable sheath? Vinyl tape does just fine, Dave said, except in a wet location, and self-sealing mastic tape does even better. Best is a layer of self-fusing tape covered by a layer of vinyl. It even can be used outdoors on UF or SE cable, so long as it is not buried. For that, you need the sealing coverings that come with a Listed underground splice kit.
Art asked whether NM or SE cable repaired in this way still meets the UL standard. Dave commented that it is tough to say. There needs to be a dialogue between the manufacturer, AHJ, and installer. A qualified installer of repair materials should be able to make a repair acceptable to the AHJ, and Southwire's warranty will remain in effect. "Qualified?" Jim Wooten asked. "Someone who has received certified training in using the material, either in an apprenticeship class, or continuing education such as is offered by tape manufacturers." Even damaged Medium Voltage cable remains warrantied, so long as the shielded jacket, which is there for mechanical protection like that of MC, is fixed using a Listed repair kit installed by a qualified person.

We hope to co-sponsor such a class with 3M or Raychem or some such organization

Roger
 

mstrlucky74

Senior Member
Location
NJ
If you have ever worked on small engines non metallic parts in carburetors are nylon and not PVC, as nylon is resistant to gasoline but petroleum based plastics are not. With THHN the nylon is over top of a petroleum based thermoplastic. Why not use an all nylon based insulation instead? I don't know. Perhaps the insulation quality of nylon is less superior, more expensive or maybe other properties come into play.

So the "T"hermoplastic is the insulation?
 

renosteinke

Senior Member
Location
NE Arkansas
I don't think I've EVER had a roll of THHN where the clear nylon covering was not split, cracked, or otherwise damaged in some manner at multiple points in the roll. Were this component essential to the insulating properties, I would have expected to see many fauted wires in my pulls. Instead, I have seen none that can be linked with the nylon jacket.

Now, I hate to burst anyone's bubble, but there's no effort made by the manufacturers to supply us with the "best" wire. They're happy to supply us with 'good enough,' and quite often the solution is found in mixing materials. The only part of the wire that needs to be tough and slick is the outside face, and the only part that needs to insulate is the part touching the wire. There's no reason that these properties have to be provided by the same material.

We only think we "know" plastic. The fact is, the plastic industry is chock full of alloys, composites, laminates, and hybrid materials. Even a simple "PVC" part has many things in the mix besides only PVC. At some point we have to trust the label.
 

kwired

Electron manager
Location
NE Nebraska
I don't think I've EVER had a roll of THHN where the clear nylon covering was not split, cracked, or otherwise damaged in some manner at multiple points in the roll.

You must be purchasing your conductors at the wrong place then. I see problems sometimes but not on every reel.
 

Steviechia2

Senior Member
Location
Massachusetts
Does this nylon jacket have anything to do with the wet location rating for thhn/thwn?
I am just thinking about all the installs of 500 mcm copper that gets pulled in underground and the outside jacket gets scraped up and is sitting in water inside of the conduits installed outside?
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Does this nylon jacket have anything to do with the wet location rating for thhn/thwn?
No it does not. THW, XHHW, RHW, etc... do not have a nylon jackets either.

BTW, straight THHN is not rated for wet locations, it must be dual rated as THHN/THWN.


Roger
 
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kwired

Electron manager
Location
NE Nebraska
No it does not. THW, XHHW, RHW, etc... do not have a nylon jackets either.

BTW, straight THHN is not rated for wet locations, it must be dual rated as THHN/THWN.


Roger

Anything with a "W" is wet location rated.

T - is for thermoplastic

R - is for rubber

X - is for Cross-Linked Polyethylene

H - is for heat rating gives you a 75C conductor

2nd H - raises heat rating to 90C conductor

N - is for nylon outer coating

a -2 in something like THWN-2 raises temp rating. THWN is only 75C conductor, THWN-2 is 90C conductor. Apparently nobody likes the idea of calling it THHWN instead of THWN-2.
 

kwired

Electron manager
Location
NE Nebraska
Exactly, and the majority do not have Nylon Jackets.

Roger

Majority of what is commonly used or what types are mentioned in code?

I think the majority of what is used is either a multi rated THHN/THWN/THWN-2, multi rated USE/RHW/RHH, or XHHW for most general purpose applications.
 

kwired

Electron manager
Location
NE Nebraska
Depends on the job and yes, see posts number 9 and 10

Roger

Content in posts 9 and 10 would be "what is mentioned in the code". Majority of them do not have nylon jacket.

Majority of what I see installed for general use is either THHN/THWN/THWN-2, multi rated USE/RHW/RHH, or XHHW.

If copper conductor just about all I ever see is THHN/THWN, if I see RHW or XHHW they are usually aluminum conductors.
 
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