Mike Dolt Enterprises
Mike Dolt Enterprises
User: cubfanbudman1, Location: Chapel Hill, NC
Asked on: Thursday, April 21, 2011 at 5:03 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:29 am EDT
Question: Have a 225 amp main breaker panel,2 can, 60 space total, single phase, using a 320 amp continuous load/400 amp non continuous load disconnect. Print calls for 3 4/0 in 2 1/2" c. Do I size my wire going to the disconnect off the continuous load or non continuous first off? Then use 4/0 from the disconnect to the panel. Max load is 221 amps on the panel. More details the better, Just looking for a little direction, thanks?
Sizing the Wire from the Main Breaker Panel to the Disconnect Continuous Load
Use the maximum continuous load value, which is 320 amps.
Non-Continuous Load
This load does not apply to this situation as the non-continuous load value (400 amps) is greater than the maximum continuous load (320 amps).Therefore, you should size the wire from the main breaker panel to the disconnect based on the continuous load of 320 amps.
Conductor Selection
According to the National Electrical Code (NEC), the minimum conductor size for a 320-amp continuous load on a single-phase system is 4/0.
Conduit Sizing
Based on the 4/0 conductor size and the use of 2 1/2" conduit, you will need to use a 3-conductor, 4/0 AW
G cable for the run from the main breaker panel to the disconnect.
Wire Sizing from the Disconnect to the Panel
Since the maximum load on the panel is 221 amps, which is less than the 320-amp continuous load, you can use 4/0 conductors for the run from the disconnect to the panel.
Conclusion Size the wire from the main breaker panel to the disconnect based on the continuous load of 320 amps. Use a 3-conductor, 4/0 AWG cable for this run.* Use 4/0 conductors for the run from the disconnect to the panel. Flag for review