Calculating running load
Running load is the electrical demand of equipment while it operates, after any starting event. A running-load calculation estimates the largest combination of loads that the generator is expected to supply continuously or for their normal operating periods.
Collect the inputs
For each load, record a recognizable name, its model, electrical input, supply voltage, and the source of the figure. Separate measured values, manufacturer specifications, and generic estimates. A cooking-power label on a microwave or a motor’s mechanical horsepower is not automatically its electrical input. [1]
If a single-phase AC load lists volts and amps, multiplying them gives volt-amperes. Real watts also depend on power factor: W = V × A × PF. Do not assume unity power factor for every appliance. Equipment data or appropriate measurement can resolve a value that a label leaves unclear. [3]
Build an operating scenario
Choose a credible set of loads that may operate together. Cycling appliances still contribute whenever their cycles overlap. A daily average derived from an electricity bill can conceal much higher instantaneous demand; it is not a substitute for a load inventory.
Illustrative worksheet: lighting at 200 W, refrigeration at 180 W, a fan at 400 W, and a selected appliance at 1,200 W total 1,980 W, or 1.98 kW, while all four are running. These invented inputs demonstrate the arithmetic and are not appliance specifications.
| Illustrative load | Running input |
|---|---|
| Lighting | 200 W |
| Refrigeration | 180 W |
| Fan | 400 W |
| Selected appliance | 1,200 W |
| Simultaneous total | 1,980 W |
Use the total correctly
The running total is the baseline for the next step, not the final generator size. Check the starting events of motors and compressors against the loads already running. Also confirm that the generator supplies the required voltage and has adequate current capacity at the relevant connections. [1] [3]
For an installed system, the designer should review circuit loading and any enforced load-management assumptions. Keep a version of the worksheet that identifies excluded loads and uncertain data. That record makes it easier to update the assessment when equipment changes instead of treating an early estimate as permanent.
Sources and further reading
- Honda — Generator wattage estimation guide ↗powerequipment.honda.com
- Honda — Generator wattage calculator ↗powerequipment.honda.com
- Cummins — Application manual T-030 ↗powersuite.cummins.com
Use the manual and nameplate for the exact model. Local requirements and site conditions take precedence over general examples.