The method, straight from our crew training
In Module 5 and Module 8 of our free crew training we teach one rule: sum the load, spread the phases, stay under 80%, and let the electrician do the wiring. This calculator runs the same sums. Watts default to the planning figures from those modules (a powered top at 400 W, a sub at 600 W, an amp rack at 1,500 W, an urn at 2,000 W). Swap in the label on your own kit.
| Set | kW (kVA × 0.8) | Highveld (−10%) | Plan for 70% | Under-loaded below 30% |
|---|---|---|---|---|
| 20 kVA | 16 kW | 14.4 kW | 10.1 kW | 4.3 kW |
| 30 kVA | 24 kW | 21.6 kW | 15.1 kW | 6.5 kW |
| 50 kVA | 40 kW | 36 kW | 25.2 kW | 10.8 kW |
Too big is a problem too. A diesel running under about 30% load for hours wet-stacks: soot, black smoke, lost power. The tool flags it and suggests a smaller set or a split.
Diesel and the 0.3-litre rule
We teach crew a simple fuel check: roughly 0.3 litres per kWh of load, plus 25% reserve. A 15 kW load for 10 hours is about 45 litres before the reserve. The calculator runs that sum alongside a manufacturer curve from a Cummins 33 kVA data sheet (3.0 to 8.7 litres an hour from quarter to full load), scaled to the recommended set. If the two disagree a lot, the set is probably badly loaded. Fill up before the event starts and refuel only when the engine is stopped and cool.
Why we often split the show from the kitchen
On bigger builds we keep the PA on its own line, lighting on another and catering and heaters on the third. Urns and fridges switching in and out put noise on the line, and you hear it in the PA. The split-generator option sizes a show set and a service set separately so you can see whether two smaller sets beat one big one.
We run our own 20, 30 and 50 kVA sets, distros and crew from a 2,000 m² warehouse with 10+ trucks. Add the result to your event brief, check sound coverage with the AV sound estimator, and run the compliance checker and our SASREA safety guide for the paperwork.
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.
Do you supply generators, distros and crew?
Yes. We hold 20, 30 and 50 kVA sets as single or three-phase units, plus 63 A and 32 A distros and leads. Click “Send to B&W for a generator quote” to email us the load sheet.
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Sources
- B&W Productions crew training, Module 5: Event Power
- B&W Productions crew training, Module 8: Event Power in Depth
- Corporate Event Planning: Load-shedding event planning contingency guide
- Cummins C33 D5 generator set data sheet (fuel consumption, ISO 8528 ratings)
- Generator Source: diesel fuel consumption chart by kW and load (cross-check)
- ROE Visual Black Pearl BP2 V2 brochure (160 W max / 80 W avg per 0.25 m² panel)
- Epson EB-L1070U datasheet (416 W)
- APC Smart-UPS runtime chart, 3 kVA models
- APC Smart-UPS SRT 3000VA datasheet (2,700 W / 3,000 VA)
- Electrical Installation Regulations, 2009: explanatory notes (gov.za)
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.