What Size Portable Generator Do You Need to Run a 240V Well Pump?

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Start with your pump's nameplate

Well pumps vary too much to size from a chart. Horsepower, motor type, and well depth all change how much power yours needs. The figures that matter are printed on the motor nameplate, the control box, or the pump maker's spec sheet.

A submersible pump's motor sits down in the well, so you may not be able to read its label. In that case, check the control box near the pressure tank, look for the original install paperwork, or ask your pump installer. An electrician can also measure the pump's draw while it runs and while it starts.

• Voltage: confirm it is a 240-volt pump
• Running amps or full load amps
• Horsepower
• Starting information, such as locked rotor amps or a code letter
• Whether the pump uses a separate control box

Do the sizing math

Generators list two figures. Running watts are what the unit can supply steadily. Starting watts, sometimes called peak or surge watts, are a short burst it can deliver while a motor spins up. A well pump needs far more power for the first moment of each start than it does once it is running.

For example, if your pump's nameplate lists 10 running amps at 240 volts, that is 2,400 running watts. Add the running watts of everything else you want powered at the same time, such as your refrigerator and some lights, using the numbers from each device's label or a plug-in watt meter. Your generator's running watts should sit comfortably above that total.

Then check the surge. For example, if your pump installer tells you your pump needs a certain number of watts to start, your generator's starting watts must cover that figure plus the running watts of whatever else is already on. Leave headroom. A generator run near its limit all the time works harder and may not start the pump on a cold day.

Why 240 volts narrows the field

A 240-volt pump cannot run from a 120-volt outlet. Some portable and inverter generators have only 120-volt outlets. Without a listed 240-volt output, a generator is off the list no matter how many watts it claims.

Read the spec sheet and the outlet panel picture before you buy. Look for a listed 240-volt output and a 240-volt outlet. Then ask your electrician whether that outlet type works with the transfer switch or interlock they plan to install. Inlets accept one plug type, and the electrician decides which plug and cord are safe for your house.

Dual fuel and the listing on this page

The listing on this page is the Champion 11,500-Watt Electric Start Dual Fuel Portable Generator. Before you rely on it for your pump, open its spec sheet and check three things: whether the 11,500 figure is running or starting watts, what it lists on propane versus gasoline, and which 240-volt outlet it has.

Dual fuel units often list different ratings for each fuel. Size against the lower of the two if you might run on either. Electric start helps when you are restarting in bad weather. Check the maker's runtime chart at a load close to yours so you know how often you will refuel.

Connect and run it safely

Never run a generator indoors, in a garage, in a basement, or near windows, doors, or vents. Exhaust contains carbon monoxide, which you cannot see or smell. Place it outdoors, well away from the house, and use carbon monoxide alarms inside.

Franklin Electric's system diagram wires the pump from the main breaker through a control box, with no plug. If yours is wired that way, there is nothing to move to an extension cord. Connecting a generator to house wiring takes a transfer switch or interlock installed by a licensed electrician. Never backfeed through a dryer outlet or any other outlet. It can energize utility lines and hurt line workers or you.

If the generator struggles to start the pump

If the generator bogs down or trips when the pump kicks on, turn off other loads first so the full surge capacity goes to the pump. If that is not enough, you need a larger generator. Do not add a soft starter or reduced-voltage starter on your own: Franklin Electric's manual says not to use one with a minimum-sized generator, because both drop the voltage and can damage the motor. Ask your pump installer. Do not keep forcing restarts on an undersized generator. That strains both the generator and the motor.

Sources

Recorded AI check: Oct 26, 2026. The sources below may include later additions. AI checks compare factual numbers and checkable claims with web sources; they do not verify every statement.

• Franklin Electric AIM Manual, 60 Hz Submersible Systems, 2026 Edition (PDF)
• 9200W Electric Start Dual Fuel Generator - 201302 - Champion Power Equipment
• 4000W Dual Fuel Inverter - 201050 - Champion Power Equipment
• Estimating Appliance and Home Electronic Energy Use, Virginia Cooperative Extension BSE-301 (PDF)
• Reliance Controls PB30 Power Inlet Box Spec Sheet (PDF)
• CPSC Safety Alert 5123: Portable Generators (PDF)

Best inverter generator for a home outage compares units from the makers' numbers. Every guide in this class is in Portable generators.

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