Difference between THWN and THWN-2?

[bob-n]

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

http://digitalmarketing.southwire.com/products/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"

[foo1bar]

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.

[Duxa]

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

[foo1bar]

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.

[Duxa]

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?

[foo1bar]

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)

[SunEagle]

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.

[Duxa]

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?

[bob-n]

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.

[Duxa]

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

[bob-n]

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.

[foo1bar]

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.

[Duxa]

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

[SunEagle]

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.

[Duxa]

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.