Size is the decision that matters most, and the one most often made by guesswork. Too small and the set trips when the motors start. Too large and you pay for fuel and maintenance you never needed. This is how the right number is actually reached.
Running load and starting load
Running load is what your equipment draws once it is going. Starting load is what it draws in the first moment — and motors, compressors and air conditioners ask for several times their rated current to get moving.
A generator has to survive that starting surge, so the rating is decided by what starts together, not just by the total on the bill. A site with one large motor can need a bigger set than a site with twice the lighting load.
| Band | Rating | Typical use |
|---|---|---|
| Standby | 20 – 30 kVA | Silent canopy sets with automatic start. Shops, clinics, homes, branch offices. |
| Commercial | 40 – 100 kVA | Daily-duty power for towers, hotels, housing societies and cold storage. |
| Industrial | 150 – 350 kVA | Prime power for production floors, mills, hospitals and campuses. |
| Heavy / Prime | 500 – 1000 kVA | Main-grid scale. Three-shift plants, industrial estates, data centres. |
kW and kVA are not the same number
Generators are rated in kVA; most equipment is labelled in kW. At the standard power factor of 0.8, kW is kVA multiplied by 0.8 — so a 100 kVA set delivers 80 kW.
Add up your load in kW, divide by 0.8, and you have a first estimate in kVA. Then allow for starting current and some headroom, which is where an engineer earns the visit.
Why bigger is not safer
A diesel engine wants to work. Run lightly loaded for long periods it wet-stacks — unburnt fuel and carbon build up in the exhaust — and it burns more fuel per unit of power and costs more to maintain for its whole life.
The aim is a set that carries your real load comfortably, not one that idles through it.
The quick way to get it right
Send us an appliance or machine list, or simply a photo of your distribution board. We run the load calculation on site before quoting, at no cost, so the rating is measured rather than estimated.
More buying guides.
Quick answers.
Not covered here? Send us your appliance list or a photo of your distribution board and we will size it for you at no cost.
Ask an engineerIt depends almost entirely on how many air conditioners must run and whether a water pump starts with them. Sets in our standby band are built for homes, shops and clinics — send us the appliance list and we will size it exactly.
Divide kW by 0.8. A load of 80 kW needs 100 kVA at the standard 0.8 power factor, before allowing for starting current.
Allow sensible headroom, not double. If a large expansion is genuinely planned, a second set paralleled later is often cheaper to run than one oversized set from day one.
A free site survey, an honest recommendation on rating, and an itemised quote with nothing buried in it. No obligation either way.
Mon – Sat, 9:00 AM – 8:00 PM