What size generator would be needed to run a 1 hp submersible well pump ?

You mention 3/4 HP in the title, and 1 HP in the post.


Motors pose an issue, that they draw much more to start. Called Locked Rotor Amperage (LRA), than once running, call Running Load Amperage (RLA)

According to NEC, a 1 HP 230 Volt motor has an RLA of 8 amps and a LRA of 48 Amps.

Any genset needs to be able to provide the peak power to start a motor.

So, using P=EI, 230 V x 8= 1840 watts, and 230 x 48 = 11,040 watts.

But, wait, these are not proper calculations for motor watts.


Missing a Code letter that should be on the pump nameplate or datasheet.

See attached chart, you will notice Code Letters for certain motors.

The Code Letter will relate to Table 430.7(B) in the National Electric Code.

SIZING A GENERATOR FOR HOME USE (http://www.gillettegenerators.com/sizing/sizing02.html)

Any genset will need to be overcome the LRA of a motor.

Hope this helps, as I realize this is as clear as mud.

Get back with the Code Letter and we should be able to get you a size.