I've got a working 7.5 HP idler running a true 5 HP (24 amp draw) 120 gallon air compressor plus my Bridgeport and a couple of other smaller motors. This motor runs on a 40 amp breaker out of a 200 amp main. I need to increase my service to accommodate a three phase welder. Is it possible to add another motor in the circuit rather than build a new larger system from scratch. My idea is to break the circuit between the existing 7.5 HP idler and the air compressor/ mill and drop each of the three legs down to a disconnect. Then from the disconnect wire the three legs into a larger motor which would feed the welder when needed but would be dropped from the circuit when not using the welder. The welder requires about 35 amps line input and outputs 250 amps at 100% duty cycle. Anyone with experience with this? I'm not sure this is feasible. I'm unsure of how big of a 'secondary idler' I'll need and unsure of how big of a motor the 7.5 HP 'primary idler' will start. What will this do to my feed from the main to the 7.5 HP motor? Will I need to increase the wire size and breaker size from the 7.5 HP motor to the 200 Amp main service, or should I wire the larger motor as the primary Idler straight from the 200 Amp Main and use the 7.5 to supply the additional power for the welder? All comments/suggestions welcome. Best regards
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