What Is an Automatic Transfer Switch?
An automatic transfer switch is an electrical device that moves selected circuits between a utility supply and a standby generator. It monitors the normal power source, detects an outage, and signals the generator to provide backup power. When utility power returns, the switch transfers the circuits back after the system confirms stable supply.
Quick Facts About Automatic Transfer Switch
Category
Generator system component
Used for
Automatic backup power transfer
Common confusion
Different from a manual transfer switch
Also called
ATS, Automatic Transfer Switchgear
Often discussed with
Generator Installation
Key Takeaways About Automatic Transfer Switch
- It separates utility power from generator power.
- It controls which circuits receive backup power.
- It is not the same as a manual transfer switch.
How Automatic Transfer Switch Works
An automatic transfer switch monitors the electrical supply feeding selected circuits. When that supply fails or falls outside the switch’s programmed limits, the switch sends a start signal to the generator. After the generator reaches operating conditions, the switch moves the selected circuits to generator power.
Related glossary terms: Service Disconnect, Main Breaker, Load Calculation.
When utility power returns, the switch checks that the supply is stable before reconnecting the circuits. The generator then completes its shutdown sequence. A standby generator may support essential circuits through the switch, while a manual transfer switch requires a person to operate the changeover. The switch must match the generator system, service equipment, and circuits it controls.
From the GMB Electric team
When we install or inspect an automatic transfer switch, we verify the connected circuits, conductor terminations, and communication with the generator. We also test the transfer sequence and confirm that utility and generator sources remain properly separated during operation.
Automatic Transfer Switch in Practice: A Real-World Example
A homeowner selects heating equipment, refrigeration, and a sump pump for generator backup. During a utility outage, the automatic transfer switch starts the generator and moves those circuits to generator power without requiring the homeowner to operate the panel.
Related Services
Related Terms
Service Disconnect
Service Disconnect is the main device that separates a building’s electrical system from the utility supply…
Main Breaker
A Main Breaker is the primary circuit breaker in an electrical panel that controls power entering…
Load Calculation
A load calculation is an electrical design assessment that estimates the power demand of a home…
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