Electrical Engineering

Generator Sizing

How to Size a Generator for Your Load: Step-by-Step Guide

Step-by-step guide to size a generator correctly with formulas, examples, calculations, and FAQs.

How to Size a Generator for Your Load: Step-by-Step Guide

Choosing the correct generator size isn’t just about keeping the lights on — it’s about protecting your equipment, saving fuel, and ensuring reliability. Proper generator sizing requires understanding power demand , power factor , and starting surges . This detailed guide walks you through the entire process with formulas, calculations, and real-world examples — perfect for homeowners, engineers, or facility managers. 🔹 Step 1: Understand the Key Terms ⚙️ Real Power (kW) vs Apparent Power (kVA) Generators are rated in kVA (kilovolt-amperes) , while most electrical loads are rated in kW (kilowatts) . The relationship between them depends on the power factor (pf) : $$\text{kVA} = \frac{\text{kW}}{\text{Power Factor (pf)}}$$ Typical values: US industrial & commercial loads: pf ≈ 0.8 Residential & purely resistive loads: pf ≈ 1.0 So, a 100 kW load at pf = 0.8 requires: $$\frac{100}{0.8} = 125 \text{ kVA generator}$$ ⚙️ Running Load vs Starting (Surge) Load Many appliances and motors draw 2 – 6× th…

About the author

Prasun Barua is a graduate engineer in Electrical and Electronic Engineering with a passion for simplifying complex technical concepts for learners and professionals alike. He has authored numerous highly regarded books covering a wide range of elec…

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