edycallison
Member
- Location
- Loma Linda, California USA
Local AHJ using John Wiles recommendations are requiring using the SUM of both the subpanel breakers and the feeder breaker when sizing the conductor.
The system is two strings of (17) Micro Inverters landing in a subpanel with two 20amp breakers, the feeder circuit in the main is a 40amp, using John Wiles guide the plan reviewer id taking the sum of (20+20+40)x 1.20 = 88 amps requiring #4 wire between the Main and Sub. This is before voltage drop, number of conductors, and temp corrections are calculated.
This is all based on NEC 2011, CEC 2013 705.12(D)(2)
705.12(D)(2) Buss or Conductor Rating: The Sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120 percent of the rating of the busbar or conductor.
In practice we use this code to determine the allowable PV backfed, Bus rating x 1.20 ? MBR. ( 225 Bus x 1.20 with 175 amp main break would be 95 amps backfed allowed. (125x1.20= 270 ? 175 = 95)
I don?t see how this would require using #4 wire for a 40amp circuit.
The system is two strings of (17) Micro Inverters landing in a subpanel with two 20amp breakers, the feeder circuit in the main is a 40amp, using John Wiles guide the plan reviewer id taking the sum of (20+20+40)x 1.20 = 88 amps requiring #4 wire between the Main and Sub. This is before voltage drop, number of conductors, and temp corrections are calculated.
This is all based on NEC 2011, CEC 2013 705.12(D)(2)
705.12(D)(2) Buss or Conductor Rating: The Sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120 percent of the rating of the busbar or conductor.
In practice we use this code to determine the allowable PV backfed, Bus rating x 1.20 ? MBR. ( 225 Bus x 1.20 with 175 amp main break would be 95 amps backfed allowed. (125x1.20= 270 ? 175 = 95)
I don?t see how this would require using #4 wire for a 40amp circuit.