110.14(C)(1)

[Isaiah]

Does anyone know when can 90 Deg C rating be used for determining conductor ampacity for 600V cable, for example XHHW-2 90Deg C wet/dry?
NEC 110.14(C)(1) limits 90 Deg C rated cable to either 60 or 75 Deg C as determined by the CB lugs. I dont see anything that alleviates that requirement.

 

[roger]

There are some items that are actually listed for 90 Deg, some examples are machined splice products, these can be used at 90 Deg ratings.

Roger

 

[Isaiah]

There are some items that are actually listed for 90 Deg, some examples are machined splice products, these can be used at 90 Deg ratings.

Roger

Thanks Roger - thats one I havent heard of.

 

[Isaiah]

If the room temperature where the cable terminates is regulated would that have any effect on utilizing the cable ampacity at the lugs?

 

[Isaiah]

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[Isaiah]

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[Carultch]

There are some items that are actually listed for 90 Deg, some examples are machined splice products, these can be used at 90 Deg ratings.

Roger

You would only be able to take credit for terminations being rated for 90C, if all the products in the same enclosure are rated for 90C. So if you install it in a panelboard or disconnect, that is likely rated for 75C, you'd have to use 75C sizing of the wire in the termination product. If you wanted to use the 90C rating, you'd have to put your splice in a separate enclosure.

One reason you might do this, is 75C sized wire just barely exceeds the capacity of the conduit you have. Maybe you are salvaging a mistake, maybe the scope expanded from what you planned on building when the rough-in was built. So you pull 90C sized wire the majority of the length, and then locally upsize it in separate enclosures to 75C sizing to connect to equipment. It also could be a value-engineering decision, although I'm skeptical of whether that would have an advantage.

The primary reason why there is value to the 90C rating of wire, is to use it for derate calculations (ampacity adjustment for bundling and temperature correction factors). The terminations would still have to meet the 75C rating (without correction/adjustment factors), but the derate calculations get to be done from the elevated wire temperature rating.

 

[Carultch]

If the room temperature where the cable terminates is regulated would that have any effect on utilizing the cable ampacity at the lugs?

As non-intuitive as it may be, ambient temperature is not a factor in the ampacity of terminations. A 200A circuit would need a #3/0 Cu wire for 75C terminations, regardless of if the ambient temperature is 20C or 40C. It's the adjustment of the wire's (usually 90C) ampacity that depends on ambient temperature.

Also, use caution when taking credit for controlled room temperature. Consider the possibility that the air conditioner/refrigeration system either fails or is shut off for maintenance, yet the circuit in question is still running at full capacity. Unless the circuit in question only would run at full capacity when the room is kept cool, I'd recommend sizing it assuming the outdoor ambient high temperature, instead of the artificially controlled temperature. Certainly for rooms that are unnaturally hotter than outdoor ambient, like boiler rooms, you'd want to anticipate an elevated ambient temperature because of heating systems within the room.