Build my own cabin - DIY projects

Is it better to run Motors on 120V or 240V?

If installing from scratch and you have the option to wire for one or the other it is generally recommended to run 240V.  There are some advantages such a little more torque and coming up to speed faster and you will have less line loss which makes a 240V a little cheaper to run.  A motor running at 240V will draw half the amps of an equivalently sized motor running on 120V.  Since you pay for your electricity by kilowatt hours (KWH) there is not a huge power savings since 120V motor at 10 A is 1200W which is the same as 240V at 5 amps (Watts = volts * amps).


Running 240V reduces voltage drop (lost in heat on supply wires) assuming you were to wire with the same gauge wire as you would for the 120V circuit.  Let's look at this example:

Assume you had a 2.5HP air compressor to wire for and you had the choice to get a 120V or 240V.  Let's say the compressor needed to be located 75 feet from the breaker panel.  The 110V version draws 14A and the 240V version draws 7 amps.  If you ran a 12AWG Romex you'd have the following:

120V motor: Drops 4V on the supply lines equal to 56W lost due to heat on supply lines

240V motor: Drops 2V on the supply lines equal to 14W lost due heat on supply lines

All things being equal, a 120 volt motor will lose 4 times more power through line loss than a 240v motor.  In the example above the line losses aren't huge but on a larger motor or on a motor that ran continuously you would realize a little savings.  



Wiring a House