Techmagician
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Here?s the question:
What is the minimum size THHN copper conductor required for a feeder supplying a continuous load of 85A and a non-continuous load of 105A while in an ambient temperature of 34C and with a total of 4 current-carrying conductors in the same raceway?
NEC 215.2 The minimum feeder-circuit conductor size conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the non-continuous load plus 125 percent of the continuous load.
Therefore calculated load is
Continuous load 85A x 125% = 106.25A
Plus Non-Continuous load +105A
211.25A
Because there is no specification for temperature rating of the terminal and the load is over 100A the 75C column of NEC Table 310.16 is used in accordance with NEC 110.14(1)(b)(2).
4/0 AWG rated at 230A is sufficient to carry the 211.25A calculated load.
This question requires two deratings, one for ambient temperature and one for multiple conductors in a raceway.
For deration the ampacity for 4/0 THHN Copper is in the 90C column of NEC 310.16 is 260A
Correction factor for 31-35C on NEC Table 310.16 is .96
Therefore 260A x .96 = 249.6A
Adjustment factor for 4-6 wires in the same raceway on NEC Table 310.15(b)(2)(a) is .80
Therefore 249.6A x .80 is 199.68A
This is where I am confused.
Is the derated ampacity required to carry the actual load of 190A or the calculated load for continuous of 211.25A? My interpretation is the actual load of 190A because of NEC 215.2 but I am not sure.
What is the minimum size THHN copper conductor required for a feeder supplying a continuous load of 85A and a non-continuous load of 105A while in an ambient temperature of 34C and with a total of 4 current-carrying conductors in the same raceway?
NEC 215.2 The minimum feeder-circuit conductor size conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the non-continuous load plus 125 percent of the continuous load.
Therefore calculated load is
Continuous load 85A x 125% = 106.25A
Plus Non-Continuous load +105A
211.25A
Because there is no specification for temperature rating of the terminal and the load is over 100A the 75C column of NEC Table 310.16 is used in accordance with NEC 110.14(1)(b)(2).
4/0 AWG rated at 230A is sufficient to carry the 211.25A calculated load.
This question requires two deratings, one for ambient temperature and one for multiple conductors in a raceway.
For deration the ampacity for 4/0 THHN Copper is in the 90C column of NEC 310.16 is 260A
Correction factor for 31-35C on NEC Table 310.16 is .96
Therefore 260A x .96 = 249.6A
Adjustment factor for 4-6 wires in the same raceway on NEC Table 310.15(b)(2)(a) is .80
Therefore 249.6A x .80 is 199.68A
This is where I am confused.
Is the derated ampacity required to carry the actual load of 190A or the calculated load for continuous of 211.25A? My interpretation is the actual load of 190A because of NEC 215.2 but I am not sure.