THHN exposed to the weather..

Status
Not open for further replies.

wire monk

Member
We installed a 400 amp service and used Thhn wire in a 3" Rigid Pipe riser.. The inspector said you can't use Thhn wire exposed because it is not sunlight resistant..You have to use XHHW. is that correct..
 

iwire

Moderator
Staff member
Location
Massachusetts
First off it had better be THWN to be in a wet location.

Beyond that if it is sunlight resistant it will be marked sunlight resistant.
 

hmspe

Senior Member
Location
Temple, TX
Occupation
PE
We installed a 400 amp service and used Thhn wire in a 3" Rigid Pipe riser.. The inspector said you can't use Thhn wire exposed because it is not sunlight resistant..You have to use XHHW. is that correct..

How exactly is wire in conduit exposed to sunlight? Inside a conduit is not exposed.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
Because there are exposed conductors to tie into the Service Drop, and these are usually your drip loop too.

I used THWN for my 400A service. The conductors were marked Sunlight Rssistant.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The "T" stands for Thermoplastic (PVC) but is not automatically "sunlight resistant" unless specifically marked as such. Many, but not all, THWN will be so marked. You will have to double check to be sure. I take it your cable was not marked THHN/THWN then? Might be worth double checking, and look for the "sunlight resistant" label while your at it.

By the way, XHHW would not be suitable either unless it too specifically says "sunlight resistant", although I think that most are marked that way.

But THHN was a no-no outside of the conduit. Read 310.8(D)
 
Last edited:

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
The inspector said you can't use Thhn wire exposed because it is not sunlight resistant..You have to use XHHW. is that correct..
Had a strong hail storm in the area three days ago. I put a 240/120 V 200 A residential service riser back on the side of a house (tree limb came down on the drop).

From the manufacturer's date stamped in the meter socket, the mast had only been up for six years.

The THHN / THWN-2 conductors were clearly stamped "Sunlight Resistant" along with all the other information.

Here's the thing that I noted: The nylon slip cover, where exposed to open air on the North face (no direct sunlight) of the building, had seperated from the insulation like a molting snake skin. The stamped label remained, as it was stamped below the nylon.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Had a strong hail storm in the area three days ago. I put a 240/120 V 200 A residential service riser back on the side of a house (tree limb came down on the drop).

From the manufacturer's date stamped in the meter socket, the mast had only been up for six years.

The THHN / THWN-2 conductors were clearly stamped "Sunlight Resistant" along with all the other information.

Here's the thing that I noted: The nylon slip cover, where exposed to open air on the North face (no direct sunlight) of the building, had seperated from the insulation like a molting snake skin. The stamped label remained, as it was stamped below the nylon.
The nylon case is there to resist abrasion while pulling, once installed it really serves no further purpose. It's not the nylon that needs to be sunlight resistant, it's the PVC (or XLP).
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Cannot be THHN inside or outside of the conduit.

Must be clearly labeled Sunlight Resistant

Bad choice for a service anyway

Huh?

Most THHN I have used here out west was labled THHN/THWN I have never seen THHN only.
So what is the problem using THHN/THWN in a riser to a service head to a drip loop as long as it says " sunlight resistive"
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Most THHN I have used here out west was labled THHN/THWN I have never seen THHN only.
So what is the problem using THHN/THWN in a riser to a service head to a drip loop as long as it says " sunlight resistive"
My point, exactly.

I think some don't understand that the period of time that the conductors look raggedy as the nylon molts off has nothing to do with the rating of the conductor.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
I don't have a 300.9. :confused:
It's new in the '08.
300.9 Raceways in Wet Locations Above Grade.

Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.8(C).

(And this is the Handbook commentary) Section 300.9, new for the 2008 Code and similar to 300.5(B), draws attention to the inside of all raceways and enclosures installed in an abovegrade wet location. The inside of these raceways and enclosures now definitively requires conductors and cables suitable for use in wet locations in accordance with to 310.8.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
It's new in the '08.
I don't have a 310.8(C) either.

I know about exterior conduit being a wet location. I thought the comment was about sunlight resistance even inside the conduit, not the lack of a W in the insulation rating.

Looking at it again, I see my error.
 
Status
Not open for further replies.
Top