Charts

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.
Electric Motor Size Minimum Generator Req’d (KVA) by Starting Method Run Power
Electric Motor Size HP KW Minimum Generator Req’d (KVA) by Starting Method D.O.L to KVA Size (Note 1) S.D to KVA Size (Note 2) Run Power KVA Used When Running (Note 3)
Electric Motor Size 1 0.75 Minimum Generator Req’d (KVA) by Starting Method 2.5 2 Run Power 1
Electric Motor Size 1.5 1.1 Minimum Generator Req’d (KVA) by Starting Method 3.75 3 Run Power 1.5
Electric Motor Size 2 1.5 Minimum Generator Req’d (KVA) by Starting Method 5 4 Run Power 2
Electric Motor Size 3 2.2 Minimum Generator Req’d (KVA) by Starting Method 7.5 6 Run Power 3
Electric Motor Size 4 3 Minimum Generator Req’d (KVA) by Starting Method 10 8 Run Power 4
Electric Motor Size 5 3.7 Minimum Generator Req’d (KVA) by Starting Method 12.5 10 Run Power 5
Electric Motor Size 6 4.5 Minimum Generator Req’d (KVA) by Starting Method 15 12 Run Power 6
Electric Motor Size 7.5 5.5 Minimum Generator Req’d (KVA) by Starting Method 18.75 15 Run Power 7.5
Electric Motor Size 10 7.5 Minimum Generator Req’d (KVA) by Starting Method 25 20 Run Power 10
Electric Motor Size 12.5 9.3 Minimum Generator Req’d (KVA) by Starting Method 31.25 25 Run Power 12.5
Electric Motor Size 15 11 Minimum Generator Req’d (KVA) by Starting Method 37.5 30 Run Power 15
Electric Motor Size 20 15 Minimum Generator Req’d (KVA) by Starting Method 50 40 Run Power 20
Electric Motor Size 25 19.6 Minimum Generator Req’d (KVA) by Starting Method 60.5 50 Run Power 25
Electric Motor Size 30 22 Minimum Generator Req’d (KVA) by Starting Method 75 60 Run Power 30
Electric Motor Size 40 30 Minimum Generator Req’d (KVA) by Starting Method 100 80 Run Power 40
Electric Motor Size 50 37 Minimum Generator Req’d (KVA) by Starting Method 125 100 Run Power 50
Electric Motor Size 60 45 Minimum Generator Req’d (KVA) by Starting Method 150 120 Run Power 60
Electric Motor Size 75 55 Minimum Generator Req’d (KVA) by Starting Method 187.5 150 Run Power 75
Electric Motor Size 100 75 Minimum Generator Req’d (KVA) by Starting Method 250 200 Run Power 100
Electric Motor Size 125 90 Minimum Generator Req’d (KVA) by Starting Method 312.5 250 Run Power 125
Electric Motor Size 150 110 Minimum Generator Req’d (KVA) by Starting Method 375 300 Run Power 150
Electric Motor Size 175 130 Minimum Generator Req’d (KVA) by Starting Method 437.5 350 Run Power 175
Electric Motor Size 200 150 Minimum Generator Req’d (KVA) by Starting Method 500 400 Run Power 200
Electric Motor Size 250 185 Minimum Generator Req’d (KVA) by Starting Method 625 500 Run Power 250
Electric Motor Size 300 225 Minimum Generator Req’d (KVA) by Starting Method 750 600 Run Power 300
Electric Motor Size 400 300 Minimum Generator Req’d (KVA) by Starting Method 1000 800 Run Power 400

NPE provides these calculators and guides to assist with general queries and recommends working with experts to ensure suitability.
NPE assumes no responsibility or liability for any errors, omissions or misuse of the contents of this site. These online tools do not constitute professional advice.
For assistance, contact any of NPE’s Australian branches.