Electrical reference chart
Generator Sizing Chart
Use this worksheet after the calculator result to record base load, starting load, load sequencing, voltage dip notes, application mode, derating, recommended generator size, fuel estimate, output current, ATS rating, and conductor review.
Quick reference table
A generator sizing chart is a calculator-led planning screen, not an order-ready generator selection. It organizes connected load, starting load, load sequencing, voltage dip, power factor, standby or prime mode, altitude and temperature derating, fuel, ATS rating, manufacturer data, utility requirements when applicable, adopted NEC checks, and AHJ requirements before equipment selection.
Generator sizing worksheet
| Checkpoint | Record from calculator | Review before selection |
|---|---|---|
| Load basis | Base kW, kVA, PF, load unit | Confirm load schedule, diversity, and essential load list |
| Starting load | Peak starting load and method | Coordinate motor starting, load sequencing, and voltage dip |
| Application mode | Standby, prime, or continuous | Confirm duty rating, runtime expectations, and code classification |
| Derating | Altitude and temperature factors | Check manufacturer data for site conditions |
| Output equipment | Generator current, ATS, conductor ampacity | Verify adopted NEC, listing, and equipment ratings |
| Fuel screen | Fuel rate and total fuel required | Confirm tank, ventilation, runtime, and logistics |
Generator decision handoff
| Design issue | Document on the chart | Why it changes the answer |
|---|---|---|
| Motor starting | Largest motor, starter method, step sequence | Starting kVA and voltage dip can control size |
| Nonlinear loads | UPS, VFD, rectifier, medical or IT load notes | Waveform and alternator heating may change manufacturer sizing |
| Transfer equipment | ATS rating, poles, bypass, service or non-service use | Transfer switch selection is not the same as kW sizing |
| Fuel and runtime | Fuel type, consumption, tank size, refill plan | Runtime can govern project acceptance even when kW is adequate |
| Site conditions | Altitude, ambient temperature, enclosure, ventilation | Derating can lower usable generator output |
How to use this chart
Record load and mode
Copy total load, load unit, power factor, application mode, starting load, and starting method from the calculator.
Document derating
Record altitude, temperature, safety factor, load growth, application factor, and manufacturer derating assumptions so the recommended size is traceable.
Prepare equipment review
Use the worksheet to list generator output current, conductor ampacity, ATS rating, fuel system, ventilation, and manufacturer checks.
Formula basis
Required generator kW = larger of base load and starting load, adjusted for growth, safety margin, application factor, and environmental derating.
- Base load is the converted kW value from the selected load unit.
- Starting load is the motor or transient load screen entered in the calculator.
- Derating reflects application mode, altitude, ambient temperature, and manufacturer assumptions.
- Recommended size is the next planning generator size above the calculated requirement.
Worked examples
Standby generator record
Record connected kW, starting kW, PF, safety margin, load growth, derating, recommended size, output current, ATS rating, and fuel estimate before requesting manufacturer review.
Motor-starting dominated load
A facility with modest running kW but one large motor should keep starting method, sequence, acceptable voltage dip, and generator response notes beside the calculator result.
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Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.