Guide to Choosing Generator to Motor Size

Some Notes for Sizing Generators

• Too small a generator will cause voltage fluctuations and damage to the generator or equipment windings.
• Too large a generator will cause engine to glaze and carbon up, due to engine loading.

Rule of Thumb

• Note 1 D.O.L. – Direct On line starting (high current starting).
• Note 2 S.D. – Star Delta (smooth starting med-high current).
• Note 3 – A dummy load or extra load will need to be applied to avoid glazing once running.

1. One horse power (1 hp) equals 0.75 kilowatt i.e. 20hp x 0.75 = 15kW
2. Warm generator up before applying load
3. Always engage load from largest to smallest
4. Have an electrician balance the load across all phases for single phase loads
5. When motor is operating, after start, requirement will be 1kva for 1hp i.e. 20hp – 20kva used when running.
6. Size the generator to run between 60-80% full load rating of generator
7. Amps available on a generator per phase = kva x 1.39. i.e. 20kva = 28amps/phase over 3 phases.