Wire sizing with table B.310.15(B)(2)(1)

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Fred B

Fred B

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Upstate, NY
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Electrician
What size wire would you use to get 100A from a USE-2 using table reference B.310.15(B)(2)(1).
1. If for 1 or 2 family 100% of load,
2. If for feeder wire to a sub panel.
My understanding is for #1 above I can size to 83% of the 100A that would give me a 2AWG in Al and 4AWG in Cu. But if it is a feeder for a sub panel as in #2 above I'd have to use a 1AWG in Al or 3AWG in Cu.
Is my understanding correct?
 
Your basic understanding is correct.
(See 310.15(B)(7) for details & limitations)
(USE, unless dual rated insulation, is for exterior use only)
 
Fred B said:
What size wire would you use to get 100A from a USE-2 using table reference B.310.15(B)(2)(1).
1. If for 1 or 2 family 100% of load,
2. If for feeder wire to a sub panel.
My understanding is for #1 above I can size to 83% of the 100A that would give me a 2AWG in Al and 4AWG in Cu. But if it is a feeder for a sub panel as in #2 above I'd have to use a 1AWG in Al or 3AWG in Cu.
Is my understanding correct?
Click to expand...
It would be #2 Al or #3 Cu.

Is USE permitted to be installed in a raceway?
 
david luchini said:
It would be #2 Al or #3 Cu.

Is USE permitted to be installed in a raceway?
Click to expand...
The last paragraph of the xxx.22 sections of the raceway articles says that cables are permitted to be installed in raceways unless prohibited by the cable article. I don't see anything in 338 that prohibits USE from being in a raceway.
 
The - 2 means it has 90C insulation not that its dual rated. The wire would also need to be marked RHW for interior wiring.
 
Fred B said:
My understanding is USE-2 is dual rated or am I wrong?
Click to expand...

The "-2" suffix, means it is rated for both 75C and 90C, in wet and dry locations. So in a way, it does mean dual-rated, but that is referring to the insulation temperature rating.

What you need to look for to determine if it can be used in a building, is if it also carries a rating in the family of RHH/RHW/RHW-2 (any of the above, and follow the details of that designation), which is the case for most USE-2 I've ever seen. Straight USE and USE-2 is restricted to its use as underground service entrance wiring as its name designates, and has restrictions against using it in other contexts, such as inside buildings. The RHH/RHW/RHW-2 designations that commonly come as a package deal with USE-2, are what you need to look for in order to get around this prohibition. The reason why wires can carry so many ratings, is to indicate backwards compatibility with previous generations of similar wire insulation technology.

The breakdown of the RHH/RHW/RHW-2 terminology is as follows:
R =rubber-like insulation, usually cross-linked polyethylene (XLPE).
Single H = heat, meaning 75C instead of 60C rating
Double H = high heat, meaning 90C
W = wet location
"-2" = dual rated for 75C and 90C in both wet and dry locations.

RHH would be restricted to dry locations.
RHW would be limited to 75C
RHH/RHW would get to use 90C in dry locations, but require 75C in wet locations
RHW-2 is the full shibang, inclusive of all of the above, letting you use the 90C rating regardless of location
 
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