How to size a diesel generator.
A practical guide to load schedules, starting currents, operating duty and the site information needed for a meaningful generator quotation.
Start with the equipment, not just a kVA target
List every load the generator will supply. Record running kW or kVA, voltage, phase, power factor and the largest starting current or load step. Identify which equipment runs together and which loads can be sequenced.
Separate running load from starting load
Motors, pumps and compressors can demand substantially more power while starting. Their starting method matters. A variable-speed drive, soft starter and direct-on-line motor present different requirements, so provide the equipment data.
Define prime or standby duty
Tell us whether the generator provides backup during a mains failure or operates as a regular source of power. Expected hours, average load and load variation affect which rating and configuration are appropriate.
Allow for the installation
Supply site altitude, ambient temperature, available space, enclosure requirements, ventilation route, exhaust route and access for delivery and maintenance. Confirm any noise limits and fuel storage requirements.
Information to send with an enquiry
- Load schedule and largest motor or load step
- Voltage, phase and frequency
- Prime or standby duty and expected run hours
- Site location, temperature and altitude
- Open or canopied format, acoustic requirement and footprint
- Changeover, automatic start and monitoring requirements
- Delivery destination and required date
Use the kW to kVA calculator for a first estimate. Then send your load schedule for a complete specification.