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Difference between THWN and THWN-2?

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  • #16
    Originally posted by bob-n View Post
    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.
    Well, the entire run will be inside of EMT, my only concern is the inspector raising questions about it not being THWN-2. If NEC says its ok to have the wire that I have up on a roof inside EMT, then I think Im good?

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    • #17
      Originally posted by Duxa View Post
      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
      That wire probably needs to be in a conduit or EMT.

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      • #18
        Originally posted by Duxa View Post
        Well, the entire run will be inside of EMT, my only concern is the inspector raising questions about it not being THWN-2.
        If the derating calculations are such that the 10 AWG THWN is OK for the amperage you're putting through it, then you're OK.
        (IMO it's doubtful the inspector will do the calculations to check on you - but I think you should still do them anyway)


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        • #19
          Originally posted by foo1bar View Post
          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.


          Yes - and that PV wire will be wire that can handle the UV exposure.

          So if neither THWN nor THWN-2 are UV rated, then what is the difference between the two?

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          • #20
            Originally posted by Duxa View Post
            So if neither THWN nor THWN-2 are UV rated, then what is the difference between the two?
            The difference is their temperature rating. And therefore what amperage you use when you're derating them for heat/bundling.

            THWN would be 75'C column, THWN-2 would be 90'C column.
            So 35A vs. 40A as your starting point when you do the derating calculation. (I'm assuming 10AWG copper)

            Since the conduit is outside, it's considered a "wet" location - so you have to do the calculation with the wire as THWN, not as THHN if you're using THHN/THWN wire.

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            • #21
              Originally posted by foo1bar View Post

              The difference is their temperature rating. And therefore what amperage you use when you're derating them for heat/bundling.

              THWN would be 75'C column, THWN-2 would be 90'C column.
              So 35A vs. 40A as your starting point when you do the derating calculation. (I'm assuming 10AWG copper)

              Since the conduit is outside, it's considered a "wet" location - so you have to do the calculation with the wire as THWN, not as THHN if you're using THHN/THWN wire.
              So as I posted on the wire pictures above, it says 90C on the jacket. Why is the wire 75C?

              90C.png

              Also, this whole de-rating thing is new to me (as I am learning as I go with my install here). Could you help me figure out, or point me where I can learn how to calculate if I am well within spec?

              Info about my system:

              10awg THWN wire in EMT for 5 wires total, 2x Hot, 2x Neutral 1x Ground
              Hot and Neutrals are coming from 2 branches of Enphase microinverters IQ7X, one branch has 7x 330w panels, other branch has 8x 330w panels. Panel amperage is 1.31A so 8 panels produce 1.31*8*1.25 = 13AMPS.

              Location is Southern California, summers can get to ~100F. EMT is on QMCC-A-12 mounts https://www.quickmountpv.com/downloa...onduit-web.pdf which brings it up about 0.8 of an inch off the roof, which is asphalt composite shingle.

              These are the panels (Microinverters are built in) - https://es-media-prod.s3.amazonaws.c...icACmodule.pdf
              Last edited by Duxa; 01-23-2020, 04:19 PM.

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              • #22
                THHN is 90C. Unless you can find something that says it's rated for 90C when used as THWN, I would assume that 90C marking is for when used as THHN. Because if it were rated for THWN with 90C I would expect them to mark it as THWN-2. Check with the manufacturer to see. Maybe it is rated for 90C in a wet condition but there is some other part of THWN-2 that they don't meet so can't label it as -2. The manufacturer should have that info readily available. Probably a PDF on their website.

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                • #23
                  I found the manufacturer's website and data sheet with a simple google search:

                  http://digitalmarketing.southwire.co.../specs/173.pdf

                  "SIMpull THHN(TM) THWN"

                  "Allowable temperatures are as follows:
                  •THHN or T90 Nylon- Dry locations not to exceed 90° C
                  •THWN-2- Wet or dry locations not to exceed 90° C or locations not to exceed 75° C when exposed to oil
                  •TWN75- Wet locations not to exceed 75° C
                  •MTW- Wet locations or when exposed to oil at temperatures not to exceed 60° C or dry locations not to exceed 90° C (with ampacity limited to that for 75° C conductor temperature per NFPA 79)
                  •AWM- Dry locations not to exceed 105° C when rated and used as appliance wiring material"
                  7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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