How Much Generator Capacity Do You Need?
Sizing a diesel generator wrong costs money either way. Oversized and you burn extra fuel at part-load, glaze the cylinders, and shorten engine life. Undersized and the DG set trips, damages sensitive electronics, and can't start heavy motors. Here's the method Mecwel Engineers uses on every load survey in Guwahati.
Step 1: List every load
Walk the site and note every device you want on backup. Group them into:
- Resistive loads — lights (non-LED), heaters, kettles. Watts = VA.
- Inductive loads — motors, ACs, fans, pumps, compressors, lifts. Watts ≠ VA.
- Electronic loads — computers, servers, medical equipment, LEDs. Add 20% for power-factor headroom.
Step 2: Convert watts to kVA
Generators are rated in kVA (apparent power), not kW (real power). For a mixed commercial load, divide total watts by roughly 800 to get kVA. So 40,000 W ≈ 50 kVA base load.
Step 3: Add starting-current headroom
Motors, ACs, lifts and compressors pull 3–7× their rated current for a few seconds at start. If you have several starting together, size for the largest starting simultaneously with the rest running:
- Small office (mostly electronic + AC): base load × 1.25
- Retail / restaurant (compressors + AC): base × 1.4
- Factory / workshop (motors + welders): base × 1.5 to 2.0
- Lift or high-inertia machinery: separate soft-starter sizing
Step 4: Add 20% future growth
Businesses grow. Adding one AC, one server rack or one extra production line can push a DG set past its limit. Sizing 20% above today's peak buys you 3–5 years of growth without a re-buy.
Worked example: a Guwahati office
- 10 × 100 W LED panels = 1,000 W
- 15 × computers + monitors (200 W each) = 3,000 W
- 4 × 1.5 TR ACs (1,800 W each running, 5,000 W starting) = 7,200 W running
- Server rack + network = 2,000 W
- Refrigerator + lift standby = 3,000 W
Base load ≈ 16,200 W ≈ 20 kVA. Starting-current headroom (×1.3) ≈ 26 kVA. Growth (+20%) ≈ 31 kVA. Right pick: a 30–40 kVA silent diesel generator.
Quick reference table
- Small shop / clinic: 5–10 kVA
- Bungalow / small office: 15–25 kVA
- Restaurant / mid office: 30–62.5 kVA
- Small factory / hotel wing: 82.5–125 kVA
- Hospital / mid factory / IT floor: 160–320 kVA
- Large factory / tea garden / mall: 500–750 kVA
- Heavy industrial / data centre: 1000+ kVA
When in doubt, get a load survey
Numbers on paper are a starting point — the real load profile only shows up when we clamp-meter your incoming supply for a day. Mecwel Engineers does this free of charge across Guwahati and Assam.
Ready to power your business? Get a free quote from Mecwel Engineers — Guwahati's authorized Greaves Cotton dealer since 1991. Call +91 97060-11988 for on-site load survey and pricing across Assam.