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We are re-routing the supply line to our pump house, where there is an extension panel with 30A 220V (pump controller) and 15A & 20A 110V breakers. It's about a 60' run from the 200A main service in the house, being placed in conduit 2' underground. The wire in place is newer 10 gauge solid copper. Is this sufficient, or what should we use?
Thanks.
Assuming the max allowed load of 24 amps for a 30 Amp circuit with #10 wire , 60 feet, there will be a 3.5 volts dropped from 240 volts, leaving 236.5 volts at the end of the circuit.
Recommended max voltage drop is 5% at the end of a branch circuit, or no more than 12 Vd, or 228 volts minimum volts supplied.
There is an issue with the starting current of the motor on long runs. A motor draws 6 to ten times the running current when starting, inversely proportional to time, which means as the motor starts and current rises to peak quickly, the current then
drops down to normal as time passes.
As the motor starts and current rises, this will increase the voltage drop, which may exceed the 5% allowed. Unless this is a very small motor, I believe you can have problems with Vd, which , over time, will affect the life of the motor.
I would recommend using #8 or maybe #6 wire to eliminate the any possibility of voltage drop effects to the motor. This does not even consider the load on the 120 volt circuits, which I assume are for minor general purpose loads, such as drill, drop light, etc.
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