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How to Size a Generator

How to size a generatorgenerator

So you’ve decided you want a standby generator to provide backup power in the event of a power cut but how do you know which size would be right for your needs?

What do I need to power?

Firstly, you’ll need to work out exactly what you want to power.

Try to keep this list to items that are essential, a fridge or freezer, a source of heating or a desk lamp for a source of light or a phone charger.

How much power do I need?

Next you’ll need to find out the individual wattage of these items.

You can find the wattage on the equipment's label or in the manufacturer's manual.

Add all these together and it will give you the combined wattage of everything you want to run.

Any device with a motor, such as a fridge or a vacuum cleaner will have a ‘start up’ wattage.

This is additional power that is required to start the motor on the device.
You will need to multiply the wattage on these items by 3 to find its ‘start up’ wattage and add this to your total.

You will now have the total wattage of all the appliances you want to run in watts which you’ll need to convert to kilowatts.

1 watt (w) = 01001 kilowatts (kW)

So if you have a total of 4800 watts, you have 4.8kW

A bit of headroom...

You don’t want to be running a generator flat out so it is advisable to build in a bit of headroom to allow the generator to work with ease and not under constant strain.

Give yourself at least 20% headroom.

Final Wattage

So your final wattage will be all the individual appliance wattages for the items you want to run together, plus the ‘start up’ wattage for items with a motor, +20% headroom.

For Example:

TV 200w = 200w
Kettle 2000w = 2000w
Microwave 1500w = 1500w
Fridge 150w x 3 = 450w

Combined wattage = 4150w

+20% = 830w

Total wattage = 4980w

Therefore you would be looking to buy a generator of at least 5kW.

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