How many watts does a well pump use?

Running watts are the easy part. Startup is where generators stall — and the motor plate matters more than a chart that does not cite a manufacturer.

Quick sizing question: what size generator for a well pump.

What to read on the plate

Horsepower, voltage, running load amps, and locked-rotor amps (when the plate lists them) are the sizing inputs. This page does not convert horsepower into watts. Champion's published bands for common well pumps are on the well pump sizing page.

The LRA trap

Locked-rotor amps are the current a motor draws in the instant before it spins. If the pump starts against pressure, or sits briefly stalled, it pulls that figure. A generator sized only to a typical startup can still trip when the plate's locked-rotor value is higher, especially with other loads already running. If the plate lists LRA, multiply those amps by the nameplate voltage. That product is the surge budget.

Sizing the generator around the pump

The pump is often the largest single surge in a home backup plan. Surge budgeting counts that one start; everything else contributes running watts.

• Pump alone: size the surge rating to the plate, then confirm on the sourced well-pump page.
• Pump plus the rest of the house: add those running watts in the calculator. Do not add a second motor's surge on top of the pump's.
• Pump plus central air: two large motors. A soft-start kit on the larger one is an electrician's question, not a watt guess.

Run the list through the generator size calculator.

Two upgrades that shrink the problem

Soft-start kit. It reduces startup current. Price it from the current listing. It is the usual fix when the generator stalls on the pump, and it matters if you later run the pump from an inverter.

Staged startup. When the generator first starts, unplug everything, start the pump alone, then add loads one at a time.

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Batteries and well pumps

The pump's startup is hard on a battery inverter. The inverter's surge rating has to clear the plate's locked-rotor figure. That surge, not the fridge, is what sizes the battery system. The battery bank sizer handles the bank once you know the inverter.

FAQ

Does a submersible pump draw more than a jet pump?

The horsepower on the motor plate controls the draw either way. A submersible and a jet pump with the same nameplate are sized from that plate, not from which one sits down the well.

Can I run a 240 V well pump off a portable generator?

Only if the generator has a 240 V output. A generator with only a 120 V receptacle will not start a 240 V pump. Check the receptacle before you buy.

How much does the pump cycle during an outage?

The pump runs when the pressure tank calls for water, not continuously. Cycle it in sessions rather than idling the generator all day. How much water you use, and how long that takes, is on the pump curve and your own use, not on this page.