Water means a 240 V motor
If your water comes from a well, no power means no water — including for flushing.[1] Most submersible well pumps run on 240 V and are hardwired, so you can’t plug them into a generator outlet.
You need a generator with a 240 V outlet (such as L14-30) and a transfer switch or interlock installed by a qualified electrician.[2] A licensed well contractor or electrician can confirm the size for your pump.[1]
Pressure tank cycles
The pump starts whenever the pressure tank drops, so like a sump pump it can start at any moment. Size the generator for its surge on top of everything else that runs together.
Well pump plus the rest of the house
Motors don’t all start in the same second, so you only add the single biggest startup jump on top of everything that’s running.
- Well pump + furnace fan + fridge: 2,575 W running, 4,850 W starting → at least 3,219 W rated (mid portable). Open in calculator
We divide the running load by 0.8 because a generator shouldn’t sit above about 80% of its rating for hours.
Questions
Can I run a well pump on a 120 V generator?
Not a 240 V pump. You need a generator with a 240 V outlet and a proper transfer switch or interlock.
Is my pump 1/2 HP?
Check the label on the pressure switch box or the pump control box, or ask the company that installed it.