I would like to buy a small generator to use when the power goes out. I need one that will run the refrig. A few lites and a water pump (it is used to run the water catchment system for the house). Is 5000 watts needed ? More /less
Thanks

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Take a look here:

Generator Sizing Chart - Yamaha Motor Corporation, USA

You have to use the wattage to start motor loads. Actual nameplate data would help. A 1/3 hp pump and an average fridge come to 1400 + 2200 or 3600 VA or watts. This assumes that they can both start simultaneously.

Lighting which would be small would be added to that. Having room to run a microwave wouldn't hurt, but at the sacrifice of turning off the other loads.

There are varients of three ways to do the transfer:

1) A transfer panel with loads pre-selected
2) A main/generator mechanical interlock switch
3) Whole house with or without load shedding

Then there is the choice of automatic or manual. Finally there is the choice of natural gas/propane and even dual fuel generators even for the small ones.

Fuel consumption and the availability can become a problem in some cases.