Table 310.16

[kwired]

So why is it that THWN-2 is built with the nylon jacket, but its common alternative of XHHW-2 is a uniform single plastic? Does the polyethlene in XLPE have better friction and wear properties for wire pulling than its PVC counterpart in THWN-2?

Nylon jacketed conductors usually pull easier. XLPE usually can take more physical abuse though.

 

[Buppy.Wahm]

Buppy do you use XHWN wire for anything? Have you ever seen it?
I dont see it in UL-44 so there is no reason it needs to be in the NEC.
I believe this was added to the code in error by CMP6 when UL-44 was 'harmonized' with Canadian and Mexican standards.
I believe the Canadian Electrical Code (CEC) calls this wire T90.
EDIT: Nevermind T90 is THHN, there is no such wire as XHWN in Canada.
Perhaps this wire exists in the Mexican standards.

Tortuga,
No, I have never used that conductor. I'm studying for my masters license in MA so I am buried in the 2020 code right now. It is a good exercise, if nothing else, in getting reacquainted with the code. That is how I found that discrepancy between the two tables. Apparently no one uses that conductor; that is probably why the error was overlooked for the entire code cycle.

 

[Dennis Alwon]

@Buppy.Wahm I sent a letter to nfpa and here is there response. It sounds like that xhwn was not supposed to be there in the first place

Thank you for contacting National Fire Protection Association (NFPA).

We have spoken to the liaison for the NEC and he states the following:

“This insulation type (XHWN) was incorrectly added by the technical committee during the 2020 revision cycle and is being corrected for the 2023 edition.”

Thank you so much for contacting NFPA.

Have a safe day.

Sincerely,
NFPA Customer Support

 

[Buppy.Wahm]

@Buppy.Wahm I sent a letter to nfpa and here is there response. It sounds like that xhwn was not supposed to be there in the first place

Thanks Dennis. I appreciate your efforts and the responses of everyone on this thread. Very professional.
Joseph Savastano

 

[tortuga]

Nice work Dennis!