Sizing a Transfer Switch for Your Generac Generator
The transfer switch is the component that connects your Generac generator to your home electrical system, and selecting the correct amperage rating is critical to ensure the switch can safely carry your home electrical load during an outage. Undersizing the transfer switch creates a bottleneck that limits which circuits can receive generator power and can create overheating risks at the switch. Here is exactly how to size the transfer switch for your Generac installation.
Match the ATS to Your Electrical Service Size
The first rule of transfer switch sizing is to match the ATS amperage to the main electrical service entering your home. The vast majority of single-family homes built in the last 40 years have 200-amp electrical service. If you have 200-amp service, you need a 200-amp ATS. If you have 100-amp service (common in older homes and smaller properties), you need a 100-amp ATS. You can confirm your service size by looking at the main breaker in your electrical panel: a 200-amp main breaker means 200-amp service.
Using a 100-amp ATS on a 200-amp service is a serious error. It creates a 100-amp bottleneck in the path between the generator and your panel. If your connected load exceeds 100 amps (which is common in modern homes with HVAC, water heater, and multiple appliances running), the undersized ATS will overheat and potentially fail. Always match the ATS rating to the service size.
200-Amp Whole-House ATS: The Standard Choice
A 200-amp whole-house automatic transfer switch is the correct and most popular choice for standard residential Generac installations. It connects to your 200-amp service entrance, passes your entire home electrical panel through to the generator during an outage, and switches back to utility power automatically when it returns. Every circuit in your home receives power during an outage without any manual circuit selection or load management. The Generac 200-amp ATS is available as a bundle with most Guardian models, including the 22kW 7325, 24kW 7326, 26kW 7328, and 28kW 7329 models that IB Lighting carries.
Load-Managed ATS: For Smaller Generators
A load-managed transfer switch (sometimes called a smart switch or managed switch) is designed for installations where the generator capacity is smaller than the full panel demand. Instead of connecting to the full 200-amp service, a load-managed switch monitors total generator load in real time and cycles non-essential circuits off when demand approaches the generator limit. This allows a 10kW or 14kW generator to provide meaningful coverage without overloading, by automatically managing which circuits receive power at any given moment.
Load-managed switches are appropriate for budget-conscious installations where a smaller generator is paired with selective circuit coverage, or for existing homes where a full 200-amp service entrance ATS is difficult to install. The tradeoff is that you do not have simultaneous access to all home circuits during an outage.
Service Entrance vs Non-Service Entrance Rated
Transfer switches are available in service entrance rated and non-service entrance rated configurations. A service entrance rated ATS can serve as the main disconnect for the electrical service, combining the utility disconnect and the transfer switch function in a single device. This simplifies installation in homes where the transfer switch replaces the existing service entrance equipment. A non-service entrance rated ATS installs downstream of an existing main disconnect. Your electrician will specify which configuration is appropriate for your home based on the existing service entrance equipment.
Generac ATS Bundle vs Separate Purchase
Purchasing a Generac generator with the ATS bundled as a kit is the most common and most cost-effective approach. Generac engineers the ATS and generator to communicate through a proprietary protocol that provides richer status reporting, coordinated startup sequencing, and simplified installation compared to mixing brands. Bundled kits from IB Lighting include the matched generator and 200-amp ATS from Generac, tested for compatibility and covered under the same 5-year warranty.
Browse our complete Generac home standby generator collection including all ATS-bundled models, or call (800) 674-9019 for transfer switch sizing help specific to your home service configuration. Free freight and insurance included on every order.