I have a 120/240 volt generator with an output of 3250 watts peaking at 3750. I want to be able to power my well water pump but I'm getting conflicting answers on whether this generator packs enough power. I'm also unsure how large my well pump is but everything else in the house is pretty standard so I'm going to say between 3/4 and 1 hp.

Consumer reports says a well pump runs about 700 watts. Multiply that by 3 to get a rough estimate of the starting wattage for the pump and you run about 2100 which still leaves plenty of wiggle room in terms of wattage.
Consumer Reports Wattage Report

Doing some other research online there are a lot of folks saying you need at least a 5k watt generator to power a well water pump. Obviously that's a far cry from what consumer reports is listing and well below the output of my generator.

I don't want to just plug it in and ruin my water pump or generator so I'm trying to find a solid answer or direction before doing so.

  • With all due respect, I have a 8500 watt generator and it will not start or run my deep water pump.
    – Nutman
    Mar 21, 2018 at 23:36

7 Answers 7


If you already own the generator I say go for it and try it out. If the generator is anywhere decent then it will regulate the voltage more than enough for a motor so you won't over power the motor with voltage. If the generator can't handle it you will not harm the motor unless you are able to stall it for an extended period of time; the generator shouldn't be harmed either it would be like trying to use a dead battery if it can't push out enough juice it just won't.

The reason I've notice that people suggest higher wattage ones is because they are typically built a little better and since they are capable of more wattage they respond to a peak significantly better, I'm going into peak discussion. Generators supply electricity on demand (even the power stations'), a household generator will produce approximately a few hundred watts at idle, as more items are plugged in/turned on demand rises and the generator senses it and runs harder. Since there isn't a preemptive notice about this, the generator will typically spike/peak higher than the demand and recovery back around what it needs to put out. A motor turning on with capacitors will typically be able to handle that lag, the capacitors will just charge up slower (almost not noticeable in most cases) and the capacitors work as rectifiers handling another other voltage changes during operation. Motors without capacitors also typically handle it but since they don't get a beginning zap from the capacitors you run a small chance of burning out your coils, imagine plugging a 220v motor under load to 110v source it will energize the coils but remain stalled.

If this is a more permanent installation (off grid scenario as opposed to hurricane prep, etc.) I recommend a separate motor starter kit - bad with naming here - before the motor or a heavy duty UPS/Battery system but for just when the power fails I think you'll be fine.


I had the very same question when I sized my generator to run my well-pump during power outages. I purchased a clamp meter for under $100 and tested the pump on household current. I simply attached the meter to the hot line and then turned on the pump. My pump is 220 volt with two hot wires so I had to multiply the results by 2. Unfortunately, I have moved-on from that home and don't remember how much power mine needed, but it was well under the 5500 watt stated capacity of my genset.

Also, it is important to note the starting current or use the "hold" feature on the clamp meter so you know the starting requirements and the running requirements.


I realize this is an old thread, but others may have the same question and benefit from my answer. I have a 3/4 hp well pump and am able to power it with my 3500 peak Champion generator - barely. The first two outages really hit it whenever the well pump needed to be run and I had to turn off everything else. This last outage the generator was unable to power the pump until my 4th try 10 hours into the power outage. My advice is get a bigger generator up front so you know it will work and you are not constantly trying to balance everything to handle the well pump.


generators are very good on handling loads of up to .5 times started value. that's our policy here in Africa. if in doubt have a motor drive (schneider) to provide soft starting current.


Complete your design for needs in power outages for water. Purchase a molded holding tank (150 gallons is a decent size). Tap into the source use of the water (probably well but could be external). Plumb the tank by directing a pipe overhead to it from the source, along with a shutoff valve. Put a float valve in the top of tank. Best way is to drill a pretty good fit and put the float valve INSIDE the tank near the lid. A Hudson valve is perfect for this. Drill a hole in top on the other side of the tank as a breather (pushes air up and out of the tank as it fills). A piece of PVC will work, doesn't have to be large and and push a piece of foam insulation into the top to let it breathe yet keep the critters and dust out. Now go to the bottom drain of the tank and plum an outgoing pipe back to your hose water system. About 3' from the tank, interrupt the pipe with a demand water pump (like an RV has). On the out end you will run the pipe over to the "T" in your water source with a shutoff to the T. Place a 12V battery to the demand pump with a 10 Watt Solar panel (like you use to run a gate opener battery charger). This keeps the battery topped off. If you lose power from your main power source (the street), you can use your regular generator just to run the well long enough to fill your 150 gallon folding tank. Then open your two valves that you installed. That way you only have to run your well whenever the tank becomes low, and your house stays pressurized.

  • 2
    This doesn't really answer the OP's question about whether or not his generator will run his pump.
    – JACK
    Jan 9, 2021 at 0:24

Depends on the depth of the well, the classification of the motor, power factor of motor, etc. For example. I have a 1 horse jet pump with a power factor of 1.65 which effectively makes it a 1.65 up motor. It has a M class rating and 64% efficiency due to the start up current form zero torque to full torque INSTANTLY. It's LRA, Locked Rotor Current, is 48.7 amps at start up Maximum. Which means surge current can be as high as 11 kw at start up. I tried to start this with a 6500 surge 5000 watt run generator and it failed miserably. Fyi. Volts time current = power (watts). This 1 H.p motor runs at 9.6 amps 240 vac. Which is 2300 watts but with p.f about 2400 watts.

Look up nameplate data on the motor and find the LRA of your pump first and size accordingly. Mine failed during a hurricane and we went without water for days having the 6500 surge generator that the seller said would work.

https://generators.smps.us/surge-current-calculator.html. Mine shows 10 to 11.19 LRA

  • This gives a lot of information but doesn't answer the OP's specific question.
    – JACK
    Aug 9, 2021 at 11:53
  • It will not run his pump. if he tries and allows low voltage and frequency for a long time he will damage his pump and or generator. The locked rotor current info would show that. In that link it actually shows you can rate 30% lower than locked rotor current normally.
    – Charles
    Aug 13, 2021 at 3:45
  • Your comment is an answer.
    – JACK
    Aug 13, 2021 at 11:35

If your well is like we use, 10Kw is probably the smallest generator you want to try on a deep well for a trailer park. We burned up a pump trying to run it on a 5.5Kw after Harvey knocked out power lines to the well. Kinda like blowing out 100 WATT speakers using a 10 WATT Amp in full clipping distortion. Yes, you can destroy big speakers on too little power. Determine the total requirements of your well and get a generator at least 10% stronger than your load. If you don't, could be an easy $8,000 or more mistake.

  • What size pump do you have ?
    – JACK
    Mar 27, 2022 at 23:51

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