310.15 (B)(16)

[inspector141]

Yep, well you should know, I guess.

I always use XHHW-2 so this never came up. Interesting.

Digging into this calculation further, situation with all the following variables:

XHHW
continuous load
ambient temp correction
75C lugs

Larger of these two:
Ampacity of XHHW from 75C column x 1.25 then pick wire size from 75C
Temp correction / ampacity rating from 90C column then pick wire size from 90C

Choose the larger wire size for calculation.

This is how I would do this. Is this correct?

XHHW in a wet location has a maximum operating temperature of 75c according to the UL White Book, 310.15(B)(16) and 310.104. So, ampacity correction begins with the 75c ampacity due to the wet location. Unfortunately, the "HH" does not always mean 90c.

 

[Dennis Alwon]

XHHW in a wet location has a maximum operating temperature of 75c according to the UL White Book, 310.15(B)(16) and 310.104. So, ampacity correction begins with the 75c ampacity due to the wet location. Unfortunately, the "HH" does not always mean 90c.

This is true but as stated most Xhhw wire is usually rated xhhw-2 in which case it would be rated 90C in wet location.

 

[inspector141]

This is true but as stated most Xhhw wire is usually rated xhhw-2 in which case it would be rated 90C in wet location.

Right, but Captainwire mentioned in his statement that temperature correction can start at 90c. However, my point was that this is only 75c insulation(wet location) for ampacity correction.

 

[captainwireman]

This forum is intense. No where does a subject get more thoroughly examined and discussed. Although I do understand the specifics of types and conditions, I still did not pick up on what I just call X wire (XHHW-2) on rooftops in the '14 code during update classes. I wonder why they came up with this. Can X wire really withstand blistering Death Valley afternoon rooftop heat? How do you interpret this change?

 

[captainwireman]

It is common practice when stripping XHHW-2 in cold conditions or due to manufacturing process that tends to merge the insulation into the copper strands, to crush the XHHW-2 intended strip length with lineman's pliers, then strip. Would you consider this a problem as far as the workmanlike manner issue? It is recommended wire should be striped in the same way a pencil is sharpened. Comments?

 

[inspector141]

This forum is intense. No where does a subject get more thoroughly examined and discussed. Although I do understand the specifics of types and conditions, I still did not pick up on what I just call X wire (XHHW-2) on rooftops in the '14 code during update classes. I wonder why they came up with this. Can X wire really withstand blistering Death Valley afternoon rooftop heat? How do you interpret this change?

The 2014 code does not require ambient temperature ampacity correction for XHHW-2 in raceways or cables when exposed to sunlight on rooftops. 310.15(B)(3)(5)(C).

 

[inspector141]

I believe it is moot also as most wiring today will be -2 so it is not an issue. I guess it could be with existing installs????? I have never heard of anyone getting tagged for this but surely it must have happened somewhere

I received a call from a contractor asking for advice about an outdoor install in a raceway. He had to correct the ampacity due to bundling, but the conductors were dual rated THHN/THWN. There was no -2. Guess where the contractors purchased the wire? One of the big box stores. So, I strolled in one of the box stores and sure enough, most of the 500 ft spools were THHN/THWN. Some gauges were -2, but most were not. Insulation only rated for 75c.

 

[Dennis Alwon]

Right, but Captainwire mentioned in his statement that temperature correction can start at 90c. However, my point was that this is only 75c insulation(wet location) for ampacity correction.

I guess I am confused... If it is xhhw-2 then correction can start at 90C. If this is NOT xhhw-2 then I agree 75C is where you start. Phew-- we do need to cover all bases. I am assuming the wire is dual rated and good for 90C but it may not be.