# Proper wire sizing?

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.

 tkrussell Posts: 9,673, Reputation: 3698 Senior Electrical & Lighting Expert #2 Jun 21, 2006, 01:48 PM

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.
 Walt3241 Posts: 1, Reputation: 10 Junior Member #3 Feb 2, 2012, 03:02 PM
You should be good to use the 10 Gauge, as you are in within and under the 100ft to have to start worrying about voltage drop on the circuit, being that it is a 240V motor, i would assume that it would be no more than 1.5-4HP moter, if that, and the max inrush you could handle would be about 8-9 amps, and then it would quickly reduce to running current. You should supply the nameplate data of the Motor and Pump together, and make sure that the motor is/or is not a capacitant start induction running motor, if it is, the initial starting current could drastically increase because of the capacitor, but if it is a gen purpose motor you should be fine with the wiring supplied. Hope I helped.
 stanfortyman Posts: 4,880, Reputation: 1326 Electrical & Lighting Expert #4 Feb 2, 2012, 05:40 PM

Quote:
 Originally Posted by Walt3241 Hope I helped.
Please keep in mind, you are saying this to an almost six year old post.

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