How an Automatic Transfer Switch Works
An automatic transfer switch (ATS) is the critical link between your generator and your home’s electrical system. Without a properly rated transfer switch, a standby generator cannot safely deliver power to your home. Understanding how this component works helps you appreciate why it is essential and how to select the right one.
The Transfer Sequence
During normal operation, your home draws power from the utility grid through the transfer switch. The ATS continuously monitors the incoming utility voltage. When it detects a power interruption (typically within a few seconds), it sends a start signal to the generator. Once the generator reaches stable operating speed and voltage, the ATS disconnects your home from the utility grid and connects it to the generator output. This entire sequence takes approximately 10 to 30 seconds depending on the equipment.
Returning to Utility Power
When utility power is restored, the ATS monitors it for stability (usually for a set delay period of 1 to 5 minutes to ensure the grid power is reliable). Once confirmed stable, the ATS transfers your home back to utility power and sends a cooldown and shutdown signal to the generator.
Types of Automatic Transfer Switches
There are two main types of ATS for residential use. A whole-house (service entrance) transfer switch handles your entire electrical panel, meaning the generator powers every circuit in your home. A load-managed (load-shedding) transfer switch uses smart load management to prioritize critical circuits, allowing a smaller generator to handle essential needs by cycling non-critical loads on and off.
NEC Code Requirements
The National Electrical Code (NEC) Article 702 governs the installation of transfer switches. A key requirement is that the transfer switch must prevent backfeed, which means utility power and generator power can never be connected simultaneously. This protects utility workers from electrocution during outage repairs. All ATS equipment must be UL 1008 listed to meet safety standards.
IB Lighting carries a full selection of transfer switches from Generac, Kohler, Cummins, and other leading manufacturers. Call (800) 674-9019 for help selecting the right switch for your system.