Standby Power Generator: Complete Guide

A standby power generator is your facility’s insurance policy against power outages. Unlike a portable generator that requires manual setup, a standby system automatically detects power loss and restores electricity within seconds.

How Standby Power Systems Work

The Automatic Sequence

When utility power fails, a standby generator system follows this sequence:

1. Utility fails — The automatic transfer switch (ATS) detects power loss
2. Start signal — ATS sends start command to generator (within 2-5 seconds)
3. Engine starts — Generator engine cranks and starts
4. Warm-up — Engine stabilizes at rated speed (5-10 seconds)
5. Transfer — ATS transfers load from utility to generator
6. Power restored — Building power back within 10-30 seconds total

When utility power returns:

1. Utility stable — ATS monitors utility for 30-60 seconds to confirm stability
2. Retransfer — Load transfers back to utility
3. Cool-down — Generator runs unloaded for 3-5 minutes
4. Shutdown — Generator automatically stops, resets for next event

Standby vs. Prime Power Generators

Feature	Standby Generator	Prime Power Generator
Purpose	Backup during outages	Primary power source
Runtime	Limited hours/year	Unlimited hours
Load factor	Variable, typically <50%	Continuous, up to 80%
Rating	Standby power (STB)	Prime power (PRP)
Price per kW	Lower	15-25% higher
Maintenance	Less frequent	More intensive

Automatic Transfer Switch (ATS)

The ATS is the brain of a standby system:

ATS Types

• Open transition: Break-before-make (brief power interruption during transfer)
• Closed transition: Make-before-break (no interruption, requires synchronizing)
• Delayed transition: Includes time delay for motor loads to coast down

ATS Sizing

The ATS must be rated for:

• Continuous current: Based on total load amperage
• Withstand rating: Ability to handle fault current
• Voltage: Matching generator and utility

Standby Generator Sizing

Load Assessment

Determine which loads must be backed up:

• Essential: Life safety, critical operations
• Optional: Comfort, non-critical
• Deferrable: Can be shed during an outage

Sizing Guidelines

Facility Type	Typical Backup %	Generator Size
Residential home	30-60%	15-50kW
Small office	50-70%	50-150kW
Commercial building	60-80%	150-500kW
Hospital	30-50%	500-3000kW
Data center	100%	1000-5000kW+

Standby Generator Installation

Site Requirements

• Concrete pad: Level, reinforced, with proper drainage
• Clearances: 3-5 feet on all sides for maintenance access
• Airflow: Adequate for radiator cooling and combustion air
• Exhaust: Directed away from building air intakes

Fuel Options

Fuel	Advantages	Disadvantages
Diesel	Most common, fuel stable for years	Requires storage tank
Natural gas	Unlimited supply (piped)	Not available everywhere
LPG/Propane	Clean burning, long storage	Requires tank, lower BTU
Dual fuel	Fuel flexibility	More complex system

Permitting

• Building permit for generator pad and electrical
• Electrical permit for ATS connection
• Environmental permit for fuel storage (above certain capacity)
• Noise variance (some urban areas have noise restrictions)

Testing and Maintenance

Weekly Exercise

Run generator for 30 minutes under load (at least 30% of rated capacity) to:

• Maintain engine lubrication
• Prevent wet stacking
• Charge batteries
• Verify automatic transfer function

Annual Load Bank Test

Test at 100% rated load for 1-2 hours to:

• Dry out exhaust system (prevents corrosion)
• Verify actual capacity
• Test cooling system at full load
• Confirm fuel consumption rates

Choose Your Standby Generator

Pauway Power manufactures standby generator sets from 20kW to 2500kW for commercial, industrial, and residential applications.

Get Standby Generator Pricing →