MIC
4 wires 310.15(B)2 derating check if this applys on your 4 wire. If it does then # 500 x 430 x 80% = 344 .
240.4(b) as Greg states you can go to next highest size . 240.6 next higest size is 350.
If 310.15(B)2 applys to your run the 350 amp breaker is what 500's are good for in this case.
As far as the raceway with 3 500's in it no derateing so 500's are good togo in that case.
If the derateing on the 4 wire applys in your case then # 600 = 475 x 80% = 380 .
240.6 next highest size breaker 400 amps.
Yoopersup
