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What size generator do I need?


The most important step in buying a generator is correctly sizing your generator to serve your needs today and in the future. You need to ensure you can power all of your equipment when the power goes out but you’ll want to make sure to keep your running costs at an optimal level, but how do you know what size generator you need?

It is extremely difficult to make use of power calculators to determine your requirement as appliances vary in the start-up and normal running load they use. The best method to determine your requirement is to have a qualified electrician conduct a load test at your premises.

  • Determine what needs to run during an outage
  • Get an electrician to do a load test for you
  • Does the generator need to switch on automatically?
  • Gensets de-reate at altitude
  • Find a suitable location for installation
  • Get a quote on the genset installation

What size generator do you need?

  • What phase genset do you require? Single or Three phase.
  • Do you need to run everything in your home or business?

Location of the Generator

  • For every 100m above sea-level, the output of your generator will de-rate by 1%.
  • Ensure that the installation location complies with health and safety regulation laws to deal with the gensets’ toxic fumes when in use.
  • Do you need a silent generator set or will an open unit suffice?
  • Environmental conditions like high temperature can reduce the generators output.
  • Generators should never be installed in a garage.
  • Where will the generator be installed? If installed in a plant room there must be an adequate ventilation to allow the intake of cool air and to expel the hot air and exhaust gasses out of the room.

Running Conditions & Cost

  • Your generator should run at an average of 70 – 80% load for the best consumption and longevity of your unit.
  • You will need to identify the starting method if you have electric motors. They can use up to 7x running power at start up.
  • Running the generator at less than 40% can cause damage the unit over time.
  • Do not overload the unit as this will damage the genset.

Care and Maintenance

  • Ensure your supplier offers backup and support should you need it.
  • Ensure your supplier has parts  available.