I'm re-using existing feeders, remove from the old load at the disconnect switch, extend it to feed a boiler (480V) with new feeders. The feeder is (2) set of #350 MCM, 3 phase with ground wire. The upstream breaker is set to 620A, and meter is installed at the boiler to monitor the power usage. The load result came back never go above 600A, but the feeders runs extremely hot. The temperature goes about 190'F at the disconnect switch. Is there any reason it happens?