Mike Dolt Enterprises
Mike Dolt Enterprises
User: fisherelectric, Location: Northern Va
Asked on: Wednesday, March 23, 2011 at 9:48 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:11 am EDT
Question: Customer has a 40 KW generator that's been wired for 120/240 volt operation with a 180 amp breaker. His house has 2 200 amp service disconnects in the garage with 4/0 SER feeders running to load centers in the basement. He wants to install 2 manual 200 amp transfer switches between the disconnects and the load centers. He wants to run 4/0 SER from the generator to a trough beside the transfer switches and then run 4/0 into each transfer switch. Is that compliant?He has gas heat and cooking and water heater. Five small AC units the largest of which has MCA 22 amps.
Yes, that is compliant.
Generator and Transfer Switch Calculations
Generator capacity: 40 kW Breaker ampacity: 180 A Generator output voltage: 120/240 V Generator output wiring: 4/0 SER
Load Center Calculations
Service disconnects: 2 x 200 A Load center feeder wiring: 4/0 SER
Transfer Switch Requirements
Transfer switches: 2 x 200 A manual Transfer switch wiring: 4/0 SER
Load Calculations
Largest AC unit MCA: 22 A Total AC unit MCA: 5 x 22 A = 110 A Other loads (gas, cooking, water heater): Assumed to be minimal (< 50 A)
Total Load Estimation
Total MCA: 110 A (AC) + 50 A (other) = 160 A
Compliance Check
Generator output capacity
40 kW is sufficient for the estimated load of 160 A.
Generator breaker ampacity
180 A is greater than the estimated load of 160 A.
Transfer switch ampacity
2 x 200 A is greater than the estimated load of 160 A.
Transfer switch wiring: 4/0 SER is rated for 230 A, which is greater than the estimated load of 160 A.Therefore, the proposed installation is compliant with the applicable electrical codes. Flag for review