Hi everyone. This is my first time posting here. I'm sure this question has been aske

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kennneth1

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Hi Everyone out there in "Mike Holt" country! My question has probably been asked before but,here goes. I have two 115 v motors for an exhaust hood on a roof top in LA. The motors pull 12.6 amps each and are a continuous load. Do I use the 75 degree table or the 90 degree table as my starting point for derating? 4-6 ccc in the conduit,4" off the roof. Any help is greatly appreciated.
Thanks everyone.

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You would use the rating corresponding to the insulation of the conductor you are installing such as 90° for THWN-2, 75° for RHW, etc.
 
Less than 100A. Unless you fit conditions below, you must size based on 60C due to terminations. You may then use the derate of that size conductor based on the particular insulation, as augie47 suggested.

110.14(C)(1)(a)
(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7).
(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60°C (140°F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.
 
FWIW, what publicgood mentioned is a direct application of 210.19(A)(1)(a)...
(a) Where a branch circuit supplies continuous loads
or any combination of continuous and noncontinuous loads,
the minimum branch-circuit conductor size shall have an
allowable ampacity not less than the noncontinuous load
plus 125 percent of the continuous load.
Click to expand...

...and what augie47 mentioned is a direct application of 210.19(A)(1)(b)...
(b) The minimum branch-circuit conductor size shall
have an allowable ampacity not less than the maximum
load to be served after the application of any adjustment or
correction factors.
Click to expand...

Each may have a different result, so you must use the larger of the two. Also, though we are talking about motors load(s), 210.19(A)(1) still applies to conductor ampacity... except a motor is never considered a continuous load under this section. All compensation for continuous operation of a motor is handled in Article 430. BTW, you must use the full-load current values in Table 430.28 in most cases... and 12.6A is not listed.
 
Also keep in mind most items you will run into these days will have 75C termination ratings on them, so most times you do use that mentioned 100 amps or less needing to use 60C conductor ampacity is when older equipment is involved.
 
kwired said:
Also keep in mind most items you will run into these days will have 75C termination ratings on them, so most times you do use that mentioned 100 amps or less needing to use 60C conductor ampacity is when older equipment is involved.
Click to expand...

The other time you must use 60C for termination rating purposes is with NM cable, but if it is NM-B (it will be if new cable) you still can use 90C values as starting point for ampacity adjustments. I think sometimes SE cable can require use of 60C, but exactly when/where depends on which edition of NEC as there has been some changes in that section.
 
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