What size generator do I need to drive one sump pump of 1/2hp?

8 Answers

  • R K
    Lv 7
    10 months ago

    look at the sump pump. it will say what watts it's rated at. get a generator with a little

    more wattage output than the pump.

  • David
    Lv 5
    10 months ago

    one HP = 745 Watts so you only need half that (373 W) to run steady state.  However, starting current draw will be much higher so to get the pump to start reliably you probably need about 1 kW.

  • 10 months ago

    The SMALLEST one available will be far larger than needed.

  • GTB
    Lv 7
    10 months ago

    At least 1 Kw electrical output

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  • Anonymous
    10 months ago

    It will require about 600 to 800 watts.  A 1.5 kw generator should be good.

  • 10 months ago

    A Harbor Freight 120 Volt AC, 1/2 HP sump pump draws 6.8 Amps.


    So If I were wanting to supply consistent power to only the sump pump, I would connect a minimum 2000 watt generator to it. Providing that the generator is not being used for anything else!

    Source(s): retired electrician
  • 10 months ago

    If you don't know the power requirements of your specific pump, there are lots of online charts to help make an estimate.  Electric motors need at least double their running current when they start. Here's a chart that suggests a 1/2 hp sump pump would require 1050 running watts, and 3250 starting watts.


    That figure of 3250 may be a little on the high side, but it will give you some breathing room.

  • 10 months ago

    look up the startup power draw of the pump's motor, or of a similar pump's motor, add 20 percent for safety and then get a generator bigger than that.

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