An automatic transfer switch is the component that makes a standby generator truly automatic. Without one, you would need to be home during every outage to manually start your generator and physically switch your home's electrical system from utility power to generator power. With an ATS, the entire process happens in seconds without any human intervention. Whether you are at home, at work, or on vacation, your generator starts and your home has power. Here is everything you need to know about automatic transfer switches.
What an Automatic Transfer Switch Does
An automatic transfer switch serves as the central control point between your home, the utility power grid, and your standby generator. It continuously monitors the utility power supply and manages the switching between power sources. Here is the sequence of events during a typical power outage:
Step 1: Detection. The ATS monitors the incoming utility voltage 24 hours a day, 7 days a week. When it detects that utility voltage has dropped below an acceptable threshold or has been lost entirely, it begins the transfer process. Most ATS units wait 5 to 10 seconds before initiating transfer to avoid reacting to momentary voltage fluctuations or brief interruptions.
Step 2: Generator Start Signal. After confirming the outage is sustained, the ATS sends an electrical signal to the generator's control board to start the engine. The generator cranks and starts, reaching operating speed within a few seconds.
Step 3: Transfer. Once the generator reaches stable operating speed and voltage, the ATS disconnects your home from the utility grid and connects it to the generator. This transfer typically takes 10 to 30 seconds from the moment the outage began. During this brief period, your home is without power, which is why critical systems like medical equipment should have battery backup for the transition gap.
Step 4: Monitoring. While the generator is running, the ATS continues monitoring the utility power. It checks the utility supply periodically to detect when grid power has been restored.
Step 5: Retransfer. When the ATS detects that utility power has returned and is stable (typically after a 5-minute verification period to ensure power does not drop again), it transfers your home back to utility power and signals the generator to begin its cool-down cycle.
Step 6: Shutdown. The generator runs for a cool-down period of 5 to 10 minutes, then shuts down and returns to standby mode, ready for the next outage.
Manual vs Automatic Transfer Switches
Both manual and automatic transfer switches perform the same fundamental function: they safely switch your home between utility and generator power while preventing backfeeding. The difference is in how much human intervention is required.
Manual Transfer Switches
A manual transfer switch requires you to be physically present during an outage. Here is what you must do every time the power goes out:
- Go outside to your portable or standby generator
- Start the generator manually (pull cord or electric start button)
- Wait for the generator to warm up and reach stable operation
- Go to the transfer switch panel (usually next to your electrical panel)
- Physically flip each circuit switch from UTILITY to GENERATOR
- When power returns, reverse the entire process
Manual transfer switches cost significantly less than automatic units, typically $300 to $800 for the switch plus $500 to $1,500 for installation. They are a practical solution for homeowners using portable generators who experience infrequent, short outages and are always home when outages occur.
Automatic Transfer Switches
An automatic transfer switch eliminates every manual step listed above. The entire process happens without any human involvement. This provides several critical advantages:
- Protection when you are away: If an outage occurs while you are at work, traveling, or sleeping, the generator starts and runs automatically. Your refrigerator stays cold, your sump pump keeps running, your security system stays active, and your pipes do not freeze
- Faster response: An ATS transfers power in 10 to 30 seconds. Manual transfer takes 5 to 15 minutes at best, assuming you are home and ready to act
- No mistakes under pressure: During a storm at 2 AM with no lights and rain pouring down, the chance of making errors during manual transfer is significant. An ATS makes no errors
- Continuous protection: Medical equipment, sump pumps, and security systems cannot wait for you to get home and start the generator manually
Automatic transfer switches cost more: $1,000 to $3,000 for the switch plus $1,000 to $2,500 for installation. However, the convenience, reliability, and peace of mind make an ATS the clear choice for most standby generator installations.
Types of Automatic Transfer Switches
Open Transition (Break-Before-Make)
The most common type for residential installations. Open transition switches briefly disconnect from the utility before connecting to the generator, creating a momentary power interruption of less than one second during transfer. This is the standard design for residential ATS units and is perfectly adequate for home use.
Closed Transition (Make-Before-Break)
Closed transition switches briefly connect both power sources simultaneously during transfer, providing zero interruption. This is typically used in commercial and industrial applications where even a momentary power loss is unacceptable, such as data centers or hospitals. Closed transition switches are significantly more expensive and are rarely needed for residential installations.
Service Entrance Rated
A service entrance rated ATS serves as both the transfer switch and the main disconnect for your home. It is installed between the utility meter and your electrical panel. This design is required in some configurations and simplifies the installation by combining two functions in one device.
Load Center Transfer Switches
Some ATS units include their own load center (circuit breaker panel) built into the transfer switch enclosure. During installation, critical circuits are moved from your existing panel to the transfer switch's load center. This design is common with essential-circuit generator systems where only selected circuits receive generator power.
Installation Requirements
Installing an automatic transfer switch is a significant electrical project that involves working with your home's main electrical service. Here are the key installation requirements:
Electrical Permit
An electrical permit is required for ATS installation in Aiken and throughout South Carolina. The installation must be performed by a licensed electrician and inspected by the local building authority. Unity Power & Light handles all permit applications and inspections as part of our installation service.
Panel Compatibility
The ATS must be compatible with your electrical panel in terms of amperage rating, bus configuration, and available space. Most homes in Aiken have 200-amp service, and ATS units are available in 100-amp, 200-amp, and 400-amp configurations. A 200-amp ATS is standard for whole-home generator systems.
Location
The ATS is typically installed adjacent to your main electrical panel, either indoors or in a weatherproof outdoor enclosure. It must be accessible for service and must have adequate clearance per electrical code requirements.
Wiring
The ATS connects to three points: the utility service entrance, your electrical panel, and the generator. Heavy-gauge wiring runs from the generator to the ATS, and the ATS connects to the panel through the existing service entrance conductors or through a new feed depending on the configuration.
Top ATS Brands for Residential Generators
Generac
Generac offers several ATS models for residential use, from basic 100-amp switches to advanced 200-amp whole-house units with load management capability. Their Nexus and Evolution controllers integrate the ATS controls into the generator's control panel, simplifying the system. Generac ATS units are designed specifically for Generac generators but can work with other brands in some configurations.
Kohler
Kohler's RXT series transfer switches are known for their robust construction and reliability. They offer 100-amp and 200-amp models with built-in surge protection and load shedding capability. Kohler ATS units are designed for Kohler generators and include OnCue Plus monitoring integration.
ASCO
ASCO is a premium transfer switch manufacturer used in commercial and high-end residential installations. Their residential-grade ATS units offer features like programmable time delays, exercise scheduling, and advanced load management. ASCO switches are brand-agnostic and work with any generator manufacturer.
Eaton
Eaton manufactures transfer switches that integrate with their electrical panel systems. Their ATS units are often specified when the home has an Eaton (or Cutler-Hammer) electrical panel, providing seamless integration between the panel, transfer switch, and generator.
Why the Upgrade Is Worth It
If you currently have a portable generator with a manual transfer switch and are considering upgrading to a standby generator with an ATS, the benefits extend beyond convenience. An ATS protects your home 24 hours a day, 365 days a year, whether you are present or not. It responds faster than any human can. It makes no mistakes. It does not need to find a flashlight, put on boots, go outside in a storm, and fumble with switches in the dark.
For homeowners with medical equipment, home-based businesses, security systems, sump pumps, or anyone who travels or works outside the home, an automatic transfer switch is not a luxury. It is a necessity. The cost difference between manual and automatic is a one-time investment that pays for itself the first time an outage occurs while you are away from home.
Unity Power & Light installs automatic transfer switches as part of every standby generator installation and also offers ATS upgrades for homeowners with existing portable generators. Call us at (803) 220-4491 to discuss your transfer switch options and get a free installation quote.