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Difference between THWN and THWN-2?

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  • Difference between THWN and THWN-2?

    Hi all, I am curious what the difference between THWN and THWN-2 are? My googling skills seems to be failing me as I cant find an answer to this question.

    Home Depot sells THHN that says THWN-2 on the jacket, Lowes sells the same brand same looking THHN that says THWN on the jacket. Both are rated to withstand oils/gasoline and are rated up to 90 degrees C.

    I know that -2 means its dual rated for wet and hot locations. But based on the jacket and the name "W" means wet, and temperature rating is the same between the two at 90C. So whats the difference then?

  • #2
    Originally posted by Duxa View Post
    Hi all, I am curious what the difference between THWN and THWN-2 are? My googling skills seems to be failing me as I cant find an answer to this question.

    Home Depot sells THHN that says THWN-2 on the jacket, Lowes sells the same brand same looking THHN that says THWN on the jacket. Both are rated to withstand oils/gasoline and are rated up to 90 degrees C.

    I know that -2 means its dual rated for wet and hot locations. But based on the jacket and the name "W" means wet, and temperature rating is the same between the two at 90C. So whats the difference then?
    The "-2" rating withstands degridation from UV light and can be exposed to the sun. The THWN or THHN need to be in a raceway (conduit or pipe). The "W" allows for installations in wet areas or outside.

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    • #3
      Originally posted by SunEagle View Post

      The "-2" rating withstands degridation from UV light and can be exposed to the sun. The THWN or THHN need to be in a raceway (conduit or pipe). The "W" allows for installations in wet areas or outside.
      Thanks. So I should be fine running THWN in EMT on the roof? Dont have to get THWN-2 ? Because I kind of already ran it before realizing that the Lowes version was different from Home Depot version. Or is the inspector not gonna like seeing THWN in EMT on the roof? The entirety of it is inside EMT and Jboxes.

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      • #4
        Originally posted by Duxa View Post

        Thanks. So I should be fine running THWN in EMT on the roof? Dont have to get THWN-2 ? Because I kind of already ran it before realizing that the Lowes version was different from Home Depot version. Or is the inspector not gonna like seeing THWN in EMT on the roof? The entirety of it is inside EMT and Jboxes.
        While I can't say exactly what the inspector will agree with, I can say that THWN in conduit (rigid, EMT, pvc) should be acceptable. If you want to run the wire exposed it will need to be "-2" rated. I believe most panels have "-2" rated wire which terminate to an MC4 connector.

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        • #5
          yeah, the Enphase trunk wires are THWN-2 rated, those will go into a Jbox, then inside of that Jbox I will transition to THWN and down EMT. From NEC perspective I should be fine? UV isnt getting into EMT/Jboxes right?

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          • #6
            Originally posted by Duxa View Post
            yeah, the Enphase trunk wires are THWN-2 rated, those will go into a Jbox, then inside of that Jbox I will transition to THWN and down EMT. From NEC perspective I should be fine? UV isnt getting into EMT/Jboxes right?
            If UV gets into a box or EMT then we all have a really big problem because the sun has heated up and sent us a very powerful CME.

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            • #7
              Originally posted by SunEagle View Post
              The "-2" rating withstands degridation from UV light and can be exposed to the sun.
              I have never seen that.
              Everything I have seen is THWN = 75'C rated in wet env. while THWN-2 is 90'C rated in wet env.

              THWN/THHN is 75/90 degree C rated. While THWN-2/THHN is 90 degree C rated for both.


              I think there's a good chance that the temperature rating doesn't really matter for the OP's use.
              Mainly it would allow multiple 10AWG circuits in a conduit and still be OK to handle 30A.
              There's a whole "derating for multiple conductors in conduit" and higher temps than 30C (86F) that should be done for the wires in the conduit.

              If you want to run the wire exposed it will need to be "-2" rated. I believe most panels have "-2" rated wire which terminate to an MC4 connector.
              I have only seen MC4 connectors on PV-wire (which has UV exposure rating)
              I would not expect to see an MC4 on a THWN/THHN wire. And I would not expect to see any THHN/THWN outside of a raceway - not unless it's rated under an additional code beyond THHN/THWN. (I don't know of any that is - but I don't claim to know every product, so feel free to prove me wrong)

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              • #8
                Originally posted by Duxa View Post
                yeah, the Enphase trunk wires are THWN-2 rated, those will go into a Jbox, then inside of that Jbox I will transition to THWN and down EMT. From NEC perspective I should be fine?
                You should do check for amp capacity of your wire after taking into account the temperature of the conduit's environment, and the bundling of conductors, and the amp capacity of the wire (using the 90C or 75C rating for that temp derating calculation.
                most likely after all the calculations for derating it'll be that your 10AWG is capable of >30A under those rules. And you'll be limited to the 30A for 10AWG because of the 60C rating at the connectors.
                But without knowing the temperature you're dealing with - or the number of current carrying wires in the conduit (nor even what size wire you're using) I can't say for sure that the ampacity after derating is unimportant.

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                • #9
                  Originally posted by foo1bar View Post

                  You should do check for amp capacity of your wire after taking into account the temperature of the conduit's environment, and the bundling of conductors, and the amp capacity of the wire (using the 90C or 75C rating for that temp derating calculation.
                  most likely after all the calculations for derating it'll be that your 10AWG is capable of >30A under those rules. And you'll be limited to the 30A for 10AWG because of the 60C rating at the connectors.
                  But without knowing the temperature you're dealing with - or the number of current carrying wires in the conduit (nor even what size wire you're using) I can't say for sure that the ampacity after derating is unimportant.
                  I am running 4 conductors plus ground in EMT on asphalt shingle roof in Southern California. All 5 wires are 10 Awg. EMT is 3/4 and about 1 inch off the roof on conduit supports. The run is about 15 feet. It’s carrying AC current from Enphase microinverters, from 2 branches, around 10 to 12 amps each.

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                  • #10
                    Originally posted by foo1bar View Post

                    I have never seen that.
                    Everything I have seen is THWN = 75'C rated in wet env. while THWN-2 is 90'C rated in wet env.

                    THWN/THHN is 75/90 degree C rated. While THWN-2/THHN is 90 degree C rated for both.


                    I think there's a good chance that the temperature rating doesn't really matter for the OP's use.
                    Mainly it would allow multiple 10AWG circuits in a conduit and still be OK to handle 30A.
                    There's a whole "derating for multiple conductors in conduit" and higher temps than 30C (86F) that should be done for the wires in the conduit.


                    I have only seen MC4 connectors on PV-wire (which has UV exposure rating)
                    I would not expect to see an MC4 on a THWN/THHN wire. And I would not expect to see any THHN/THWN outside of a raceway - not unless it's rated under an additional code beyond THHN/THWN. (I don't know of any that is - but I don't claim to know every product, so feel free to prove me wrong)
                    If you check most wire insulation ratings; THWN, THHN, XHHW, etc. that have a "-2" on the end are considered PV wiring. The temperature or environment rating is listed based on the first part of the insulation rating. PV wire also has a UL 4703 listing.

                    You can purchase PV wire that can be run exposed on a roof that already includes the MC4 connector. You would then run that wire into a junction box where you can continue with standard wire insulation leaving the junction box in a conduit as long as it is rated for the environment (wet or dry).

                    You are correct in that the AWG rating is in respect to the amount of amps the wire can carry. That wire is de-rated based on the number of wires that run in the same conduit as well as the temperature it will be exposed to.

                    Although I have been out of the business for a while and could be wrong with my statements.
                    Last edited by SunEagle; 01-22-2020, 10:59 AM.

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                    • #11
                      Thanks for the insightful discussion ya'll.

                      I looked at the Jacket, its Southwire E51583.

                      Here is the picture of the jacket, sorry for crap photo as it was hard to take it while holding phone in one hand - https://imgur.com/a/t0VKTwT

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                      • #12
                        Originally posted by SunEagle View Post
                        If you check most wire insulation ratings; THWN, THHN, XHHW, etc. that have a "-2" on the end are considered PV wiring.
                        I do not believe that most THHN/THWN-2 is also listed as type PV. I'm not aware of any THHN/THWN-2 that's also type PV.
                        I do see that at least one product their 10 AWG type PV is also listed as RHH/RHW-2 and USE-2

                        Bottom line - the THHN wire at HD and Lowes is not listed as type PV (or another type that's rated for UV exposure). It's not listed for use outside of a conduit/raceway.
                        So it shouldn't be used that way.

                        You can purchase PV wire that can be run exposed on a roof that already includes the MC4 connector. You would then run that wire into a junction box where you can continue with standard wire insulation leaving the junction box in a conduit as long as it is rated for the environment (wet or dry).
                        Yes - and that PV wire will be wire that can handle the UV exposure.


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                        • #13
                          In your use, the wire isn't exposed to UV, so you're fine.

                          A common problem is that people will use cable ties to secure wire outdoors, and forget that the cable ties must be UV rated as well as everything else. Most often, black cable ties are UV safe and white ones are not.

                          By the way, it appears that E51583 is a factory identifier, not a product identifier and not of any use unless you have a warranty problem. You need to go by the THWN and THHN markings.

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                          • #14
                            Originally posted by bob-n View Post
                            In your use, the wire isn't exposed to UV, so you're fine.

                            A common problem is that people will use cable ties to secure wire outdoors, and forget that the cable ties must be UV rated as well as everything else. Most often, black cable ties are UV safe and white ones are not.

                            By the way, it appears that E51583 is a factory identifier, not a product identifier and not of any use unless you have a warranty problem. You need to go by the THWN and THHN markings.
                            Ah ok, does the jacket picture give any more info?

                            JK2aCIN.png

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                            • #15
                              The only other clue is that it is also MTW rated. Again, that doesn't give any sort of UV rating. It's good wire, but not for use directly in the sun.

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