Emergency Power System Design
Load Analysis Methodology
Proper generator sizing requires understanding both continuous running loads and transient starting loads. Motors, compressors, and HVAC systems can draw 3-7× their rated power during startup, creating brief but critical demand spikes that must be accommodated.
This calculator uses the largest motor starting method: it assumes the largest motor starts first while all other loads are already running. This is the industry-standard approach per NFPA 110 and IEEE 446.
Key Sizing Factors
- Starting Factor: Motor inrush current multiplier (3-5× for standard motors, 1× for resistive loads)
- Power Factor: Ratio of real power to apparent power (0.8 typical for mixed loads)
- Safety Margin: Overhead for future expansion and load diversity (20-30% recommended)
- Altitude Derating: Diesel engines lose ~1% power per 100m above 1000m elevation
- Fuel Consumption: Approximately 0.3 L/kWh at 75% load for diesel generators
NFPA 110 Compliance
The National Fire Protection Association Standard 110 defines requirements for emergency and standby power systems. Generators must be sized to handle 100% of the emergency load plus any legally required standby loads. Monthly testing under load is mandatory to verify capacity.
Technical Standards & References
REF [NFPA-110]
NFPA (2022)
Standard for Emergency and Standby Power Systems
“Defines sizing requirements and testing protocols for emergency generators.”
REF [IEEE-446]
IEEE (1995)
Recommended Practice for Emergency and Standby Power Systems
“Technical guidance for load calculations and generator selection.”
REF [NEC-700]
NFPA (2023)
National Electrical Code Article 700: Emergency Systems
“Electrical code requirements for emergency power installations.”
Mathematical models derived from standard engineering protocols. Not for human safety critical systems without redundant validation.