Reply by Bill Davis

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Posted on MORE Power!!! 120 vs 240 volts

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Bill Davis

226 posts in 3976 days

#1 posted 05-15-2008 03:51 AM

It will be some benefit though how much depends on the resistance in the wiring circuit. It will make the most difference if your wiring is undersized because since the 220 v motor draws half the current there will be only 1/4 the power loss in the wiring. Power loss in the wire is I^2 x R so if the current is halved the power loss is reduced by a factor of 4.

Let’s say the total resistance feeding power to the motor is 2 Ohms and the motor draws 10 Amps at 120 V and 5 Amps at 240 V. At 120 volts the power loss is I^2 x R or 10^2×2=200 watts lost in the wiring. At 240 volts 5 ^2×2 = 50 watts lost in the wiring. That is 1/4 the power loss. Now my numbers are made up and the resistance is way higher than you should experience in real life. It does illustrate however that there may be an advantage in using 240 volt wiring. Marchb said you cut it in half but in fact you cut in by 1/4th. Because you cut the power loss in the wiring that much it may actually therefore provide more power to the motor especially at motor starting where the starting current of a motor might be 10 times the running current. The I ^ 2 factor is significantly more important at the higher current draw at statrup.

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