Right-Sizing Your Generator: The Calculation That Saves You Thousands

Right-Sizing Your Generator: The Calculation That Saves You Thousands

Nameplate numbers do not tell the full story. The calculation that determines whether your generator will perform reliably for 20 years is more complex than most suppliers let on.

Why Simple Calculations Fail

Adding up the nameplate ratings of your equipment and selecting a generator to match is a starting point, not a methodology. It ignores the dynamic behaviour of electrical loads, the interaction between different load types, and the real-world conditions under which your generator will operate.

The result is either an oversized unit wasting capital and fuel, or an undersized unit that fails under load at the worst possible moment.

The Factors That Actually Matter

A proper load calculation accounts for:

  • Motor inrush currents - motors draw five to seven times their running current at start-up
  • Harmonic distortion - VFDs, UPS systems, and LED drivers all introduce harmonics that derate generator capacity
  • Power factor - loads with poor power factor require more generator capacity than their kW rating suggests
  • Load sequencing - the order in which loads are connected affects peak demand significantly
  • Ambient temperature - generators derate in high ambient temperatures; a unit rated at 20 degrees may deliver less at 35 degrees
  • Altitude - air density affects engine output; high-altitude sites require derating calculations
  • Growth margin - a 15 to 20 percent headroom for future load additions

EA Power's Site Survey Process

Every EA Power project begins with a site survey conducted by our engineers. We measure actual load profiles, assess equipment characteristics, review existing electrical infrastructure, and model the complete system before specifying a single component. This is not a desktop exercise. It is a rigorous engineering process that forms the foundation of every reliable installation we deliver.
 

Correct sizing from the outset eliminates the cost of oversizing, reduces fuel consumption, extends engine life, and prevents the catastrophic cost of undersizing. Over a 20-year asset life, the difference between a correctly sized and an incorrectly sized generator can run to tens of thousands of pounds.

16 May 2026

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