Single-phase vs three-phase diesel generators: choose by your loads

Start with the equipment and supply

Match the generator’s phase and published voltage to the equipment that must run. Ask your electrician to confirm the supply, neutral and earthing arrangements and transfer equipment. A kVA figure alone does not identify the correct electrical configuration.

Single-phase options in the catalogue

Cummins C22D5-1P and C33D5-1P are listed as single-phase models, with 20/22 kVA and 30/33 kVA prime/standby ratings respectively. The Blackwell B30GH-1ph is also single phase, but its published ratings are 26 kVA prime and 28 kVA standby, not 30 kVA.

Three-phase options in the catalogue

Cummins C22D5 is listed as three phase at 20 kVA prime and 22 kVA standby. FG Wilson FB100-4A is three phase with published 415/230 V, 50 Hz and 100 kVA prime output. Confirm the final voltage and configuration for the actual supplied model rather than treating a UK nominal supply voltage as a universal product specification.

Mixed loads and phase balance

Some installations combine single-phase circuits with three-phase motors. Ask for the permitted load on each phase and the manufacturer’s unbalanced-load limits. Do not assume that the entire three-phase rating is available on one single-phase circuit.

Starting current, starting method and the sequence of motor starts still matter. Have the proposed set checked against both running and starting loads, not just the total nameplate kVA.

What to include in your enquiry

Send equipment voltage and phase, running kW/kVA, power factor, starting details, load sequence and expected operating hours. Include your delivery postcode and offload requirements; transport is quoted separately from the generator price.