How the sizing works
Power planning is three sums. Add up the running watts of everything that plugs in. Convert to kVA by dividing by 0.8, because generators are rated at a 0.8 power factor. Then leave headroom so the set isn't flat out when the urns boil and the DJ drops the bass. Our load-shedding contingency guide recommends sizing at 1.5× your calculated requirement, so the calculator defaults to planning the set at 67% load. Change it if your electrician prefers another margin.
On the Highveld the tool also takes off about 10% for altitude, plus 5% on a hot day, following the B&W crew-training method in Event Power in Depth.
| Generator | Usable kW (×0.8) | Highveld, at 67% load | Typical job |
|---|
| 20 kVA | 16 kW | ≈9.6 kW | DJ, small PA, lighting, a bar |
| 50 kVA | 40 kW | ≈24 kW | Conference with LED wall and catering |
| 100 kVA | 80 kW | ≈48 kW | Gala with full production and kitchen |
The guide's rough bands (20–40 kVA for a 50–100 guest event, 80–150 kVA for a 200–500 delegate conference) are a sanity check. Your load sheet beats any rule of thumb, because an LED wall or three food trucks can double the number.
Fuel, phases and the numbers to give your electrician
Diesel use is estimated from a manufacturer curve: a Cummins 33 kVA set burns about 3.0 litres an hour at quarter load, 4.4 at half, 6.1 at three-quarters and 8.7 at full load. The tool scales that per kVA for the set it recommends and adds a 25% reserve. A conference running 10 hours on a mid-size set can need well over 100 litres, so agree who refuels and when (engine stopped and cool).
Anything over about 25.6 A at 230 V goes three-phase, and the load sheet shows a phase plan: sound on L1, lighting and video on L2, catering on L3. Hand that sheet to the electrician who designs the distribution and signs the certificate of compliance. The calculator gets you to the right conversation. It doesn't replace that sign-off.
Backup for load-shedding
If the venue has its own generator, the question is what it covers and how fast it switches over. Typical switchover is 5–30 seconds, enough to crash projectors and drop a live stream, so the tool sizes a UPS for the critical kit: FOH desk, laptops, LED processor and comms. Ask the venue the ten questions in our guide, then add the generator line to your event budget and your event brief. Running an outdoor build? Pair this with the tent calculator and read our SASREA safety guide.
Frequently asked questions
How do I convert kW to kVA for a generator?
Divide by 0.8. Generators are rated in kVA at a power factor of 0.8, so a 20 kVA set gives about 16 kW and a 50 kVA set about 40 kW. Then leave headroom: the calculator plans for the set to run at roughly 67–70% of what's left after altitude and heat derating.
Why does altitude matter in Gauteng?
Engines breathe thinner air on the Highveld (about 1,500–1,800 m), so a set delivers less than its sea-level rating. B&W's crew rule of thumb is to budget about 10% less, and about another 5% on a hot day. The manufacturer's derating table is the real number.
When do I need three-phase power?
When the total load is over about 25.6 A at 230 V (a 32 A single-phase outlet at 80%), roughly 5.9 kW. Above that, use a three-phase supply and spread the load: sound on L1, lighting and video on L2, catering and heaters on L3.
How much diesel will the generator use?
It depends on the set's size and how hard it's working. The calculator uses the litres-per-hour curve from a Cummins 33 kVA data sheet, scaled per kVA, and cross-checks it against the 0.3 litres per kWh rule of thumb. It adds a 25% reserve. Check the plate on the actual set.
Do I still need a UPS if there's a generator?
For critical kit, yes. Switchover from mains to generator typically takes 5–30 seconds, which resets projectors, lighting desks and streams. A UPS on the DJ or FOH desk, laptops, LED processor and comms bridges that gap.
Can B&W supply the generator and crew?
Yes. Click “Send to B&W for a generator quote” and your email app opens with the load sheet filled in, addressed to [email protected]. The team quotes the set, distribution, cabling and crew.
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Planning estimate only. This calculator does not replace an electrical design. A registered electrician must design and sign off distribution, earthing and protection, and issue the certificate of compliance (the Electrical Installation Regulations, 2009 require a valid certificate of compliance for an electrical installation, issued only by a registered person). Generators must stand away from guests, tents and air intakes, with the exhaust downwind, never in an enclosed space. Follow venue and municipal requirements. Wattages marked "planning assumption" are typical figures, not specifications: use the label or plate on your own equipment.
