Table 310.16

[Buppy.Wahm]

In Table 310.16 there are duplicate entries in the 75 degree C column and the 90 degrees C column for 3 types of insulation. THHW, XHHW and XHWN. In Table 310.4(A) THHW and XHHW each have an application provision that limits the ampacity to the 75 degree C column when installed in a wet location. However XHWN is listed only for use at 75 degrees C dry or wet in Table 310.4(A). So, why is XHWN listed in the 90 degree C column in Table 310.16?

 

[infinity]

So, why is XHWN listed in the 90 degree C column in Table 310.16?

I don't see XHWN in T310.16.

90°C (194°F)
Types TBS, SA,
SIS, FEP,
FEPB, MI,
RHH, RHW-2,
THHN,
THHW,
THW-2,
THWN-2,
USE-2, XHH,
XHHW,
XHHW-2, ZW-2

 

[Dennis Alwon]

In Table 310.16 there are duplicate entries in the 75 degree C column and the 90 degrees C column for 3 types of insulation. THHW, XHHW and XHWN. In Table 310.4(A) THHW and XHHW each have an application provision that limits the ampacity to the 75 degree C column when installed in a wet location. However XHWN is listed only for use at 75 degrees C dry or wet in Table 310.4(A). So, why is XHWN listed in the 90 degree C column in Table 310.16?

The reason is that those insulations have 2 values. If it is installed in a wet location than it is rated 75C 90C for dry location

Look at Table 310.104(A) in the 2017 nec

 

[Buppy.Wahm]

I am using the 2020 code book. That is what we are governed by in Massachusetts. Older versions of the code, 2014 and 2017 have a different list of conductors in the 90 degrees C column and older versions of the code use table 310.15(B)(16). Those versions of the code do not list XHWN but the 2020 code does. See my original post and table 310.4 that I reference in the 2020 version of the code that lists the temperature limitations of the conductors.
Unless I am reading something incorrectly, there is a discrepancy between table 310.4 and table 310.16

 

[Buppy.Wahm]

Thanks Dennis, I saw your reply. I am aware of the difference for use in Wet and Dry locations. That is why I posted the question. The Table 310.104(A) in the 2017 Code that you reference lists XHWN for both wet and dry locations at 75 degrees C and XHWN-2 for both wet and dry locations at 90 degrees C. but neither of those conductors are listed in 310.15(B)(16) of the the 2017 code book.
I am looking for someone to answer my questions with respect to the NEC 2020 Code and respond to the discrepancy that I noted between table 310.4 and table 310.16.

 

[LarryFine]

I've never heard of XHWN, but the -2 suffix means the wet rating equals the dry rating for any insulation type.

 

[Buppy.Wahm]

Larry, You are correct about the -2 designation but my question is about the XHWN conductor.

 

[Carultch]

Larry, You are correct about the -2 designation but my question is about the XHWN conductor.

XHHN, XHWN, and XHWN-2 are new in the 2020 NEC.

They map directly onto the same columns as other columns with similar patterns to their designations.

X = cross-linked polyethylene, the material of the insulation
HH = high heat for 90C
H = heat for 75C
W = wet location
N = nylon jacket
-2 = dual rated for 75C/90C regardless of wet or dry location

XHHN = 90C in dry locations
XHWN = 75C in wet locations.
XHHN/XHWN without a -2 = 90C in dry locations, 75C in wet locations
XHWN-2 = 90C in both wet and dry locations

I'm skeptical that you would even find this wire without the "-2" designations, because the "-2" designation on similar families of wire types have been common for the last decade. On occasion, I've seen smaller wires in the THWN-2 family not carry the "-2" designation.

 

[Dennis Alwon]

I too doubt that you will find any of these wires without the -2 insulation. Older installations YES but not new conductors.

 

[david luchini]

Larry, You are correct about the -2 designation but my question is about the XHWN conductor.

The answer to your question is that it appears to be a mistake. XHWN shouldn't be in the 90 degree column.

 

[kwired]

Has anyone ever seen an XH*N (with nylon outer jacket)?

AFAIK main advantage of the nylon jacket on type T conductors has mostly been for gasoline and oil resistance.

 

[LarryFine]

AFAIK main advantage of the nylon jacket on type T conductors has mostly been for gasoline and oil resistance.

I've heard it's (also) for abrasion resistance.

 

[Carultch]

I've heard it's (also) for abrasion resistance.

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?

 

[Buppy.Wahm]

David Luchini, Thank you. That is my point. The code book has listed XHWN in the 90 degree C column in table 310.16 and it does not belong there according to Table 310.4. Table 310.4 is poorly designed and could be easily made more user friendly by adding separations in the Maximum Operating Temperature column and the Application Provisions column where dual applications are permitted based on operating temperatures.

 

[tom baker]

XLP is a cross linked insulation and is a much better insulation. It does pull harder than PVC insulation, and does not melt as PVC insulation does

 

[tortuga]

Has anyone ever seen an XH*N (with nylon outer jacket)?

AFAIK main advantage of the nylon jacket on type T conductors has mostly been for gasoline and oil resistance.

Were discussing a ghost wire here, I am almost 100% sure it does not exist.
I have been looking for it since 2018, I should offer a reward six pack if found:

XHHN - XHWN-2

Greetings all the 2017 Code was changed to add XHHN, XHWN, XHWN-2 T 310.104(A) I assume this is a XHH with an outer Nylon jacket? I am not familiar with this marking, does anyone use this stuff? Thanks in advance.

forums.mikeholt.com

 

[tom baker]

David Luchini, Thank you. That is my point. The code book has listed XHWN in the 90 degree C column in table 310.16 and it does not belong there according to Table 310.4. Table 310.4 is poorly designed and could be easily made more user friendly by adding separations in the Maximum Operating Temperature column and the Application Provisions column where dual applications are permitted based on operating temperatures.

That is an excellent observation. There have been many changes to the NEC to improve usability. We old times overlook those sections. I would like to recommend you make a PI for a change to the 2026 NEC. Changes will be accepted in the fall of 2023. We have a topic here on changes to the NEC and can help you with it.

 

[tortuga]

Ok I am officially offering a reward, to the first person that can get me a 2 foot piece of XHHN or XHWN-2 with the printing clearly on it, #8 or larger copper.
$20 starbucks gift card

 

[Buppy.Wahm]

That is an excellent observation. There have been many changes to the NEC to improve usability. We old times overlook those sections. I would like to recommend you make a PI for a change to the 2026 NEC. Changes will be accepted in the fall of 2023. We have a topic here on changes to the NEC and can help you with it.

Thanks Tom. I would appreciate the help in submitting the PI. It is unfortunate that I have to wait almost 2 years to do that.

 

[tortuga]

It is unfortunate that I have to wait almost 2 years to do that.

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.