Generator Sizing for Construction: How Many kVA Do You Really Need?
Undersized generators trip breakers and stall motors; oversizing burns fuel and money. The sweet spot comes from listing your loads, understanding surge (starting) currents, and converting kW to kVA with a realistic power factor. This guide gives you a straightforward method used by our rental team to match your tools—mixers, air compressors, welders, tower lights—to a reliable, efficient diesel generator for Dubai conditions.
Step 1 — List Your Loads
- Concrete mixer: 2–3 kW (motor load)
- Air compressor: 4–7 kW (higher on startup)
- Hand tools (grinders, drills): 1–2 kW combined peaks
- Tower lights: 1–2 kW each depending on lamps
- Welders: verify plate ratings; some draw large surges
Step 2 — Apply Diversity & Surge Allowance
Not all tools run simultaneously. Apply a diversity factor (often 0.6–0.8 for mixed tools), then add surge allowance for motors. A simple rule is to multiply major motor loads by 1.5× to cover inrush. For example, if your running total is 10 kW with a 4 kW compressor and 2.5 kW mixer, add ~3 kW for surge, bringing the provisional total to ~13 kW.
Step 3 — Convert kW → kVA
Use kVA = kW / PF. On construction sites, assume PF ≈ 0.8 unless you have measured data. With 13 kW: 13 / 0.8 = 16.25 kVA. Round up to the nearest available frame size—e.g., a 20 kVA set gives breathing room for tool swaps and weather.
Distribution & Cables
Use a site distribution board with correct breakers for each circuit. Keep cable runs short and sized to limit voltage drop, especially for motor loads. In hot conditions, derate current capacity—or simply choose thicker cables.
Fuel & Runtime
Check the generator’s fuel burn at 50–75% load. Many jobs run best when the set is loaded above 40%, where engines are happiest and wet-stacking is minimized.
Special Cases: Welders & Large Compressors
Arc welders and big compressors can show high momentary draw. If your welder plate lists 6 kW but field experience shows nuisance trips, upsize to the next kVA range or consult us for a set with strong transient response and AVR suited for motor starts.
Rental Tips That Save Money
- Match booking to actual working days to avoid idle weekends.
- For 3–5 day jobs, compare weekly vs daily rates.
- Bundle tower lights, DBs, and cables for package pricing.
- Confirm delivery access and pad size; towing delays add cost.
Suggested images: (1) Generator with distribution board (alt: “Diesel generator rental Dubai”) (2) Electrician checking kVA meter (alt: “Technician sizing generator load”).