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What size generator do you need for a well pump?
Updated
Start with volts, not watts. Most well pumps run on 240 volts, and many portable generators only make 120. Of the five generators on this site, only the two open-frame picks have 240 volt outlets. After that, size by the pump's label, and leave plenty of room for the starting burst.
Step 1: check the voltage
Look at the pump's control box, the label on the pressure switch wiring, or the breaker in your panel. A double-wide breaker usually means a 240 volt pump. The three inverter picks here are 120 volts only, so they cannot run a 240 volt pump at all, no matter how many watts they make.
Step 2: find the running watts
Our calculator does not have a well pump line, because well pumps vary too much by horsepower and depth. Use your own label. Multiply volts by amps. For example, a label that reads 240 volts and 10 amps works out to 2,400 running watts. That is an example, not your pump. Type your number into the "anything else" box in the wattage calculator.
Step 3: leave room for the start
A pump motor needs a short burst well above its running watts to get going. In our calculator's typical figures, a refrigerator needs about three times its running watts for a moment (700 running, 2,200 to start). A deep well pump pushing water up a long pipe can be harder to start than that. The pump maker or your well installer can give you the real starting figure. If you cannot get it, size up instead of down.
The two picks with 240 volts
| Generator | Running watts, gas | Peak watts, gas | Running watts, propane | 240V outlets |
|---|---|---|---|---|
| Westinghouse WGen5300DFcv | 5,300 | 6,500 | 4,800 | L14-30R 30A |
| Westinghouse WGen9500DF | 9,500 | 12,500 | 8,500 | L14-30R 30A and 14-50R 50A |
- The WGen5300DFcv suits a smaller pump plus a few essentials. It lists a CO shutoff. The caveat: it is recoil start, and owners are split on noise.
- The WGen9500DF gives the most room for a hard-starting pump along with the rest of the house. The caveat: it weighs 210 pounds, and the listing we read did not mention a CO shutoff sensor.
See both next to the other picks on the roundup page.
You will need an electrician for this one
A well pump is wired into the house. There is no plug to move to an extension cord. To run it from a generator you need a transfer switch or an interlock kit at the panel, installed by a licensed electrician. ESFI says never to connect a generator to household wiring without a transfer switch, because power can flow back up the line and electrocute utility workers. Never backfeed through a dryer outlet to reach the pump. This page is general information, not electrical advice.
Safety first, every time
- Carbon monoxide kills. Never run a generator indoors, in a garage, in a shed or on a porch, even with the door open. Keep it at least 20 feet from the house. Point the exhaust away from windows, doors and vents. Put battery CO alarms inside your home.
- Never backfeed. Do not plug a generator into a wall outlet or dryer outlet. It can kill a utility worker or a neighbor and can start a fire. To power home circuits you need a transfer switch or an interlock kit, installed by a licensed electrician.
- Without that, run heavy-duty outdoor extension cords from the generator straight to each appliance.
- Let the engine cool before you refuel. Store fuel outside the house.