Emergency Generator Sizing
Size standby generators including motor starting and step loading.
NEC Article 700 Requirements
- Generator must start and assume load within 10 seconds (700.12)
- Fuel supply for Class 1 Level 1: 2 hours minimum
- Monthly testing required under load (700.3)
- Transfer equipment must prevent interconnection (700.5)
- Emergency circuits must be kept separate from normal circuits
Generator Sizing Considerations
Motor Starting
Motors draw 3-8x FLA during starting. Size generator for peak starting current plus running loads.
Step Loading
Maximum step load typically 1/3 of generator rating. Sequence loads for best performance.
Power Factor
Generators rated at 0.8 PF. kVA = kW / PF. Low PF loads reduce real power capacity.
Tip: Add 20-25% safety factor for future expansion and non-linear loads. Consider harmonics from VFDs and UPS systems.