Contractors 
Contractors What Are Split Bus Panels?
Split bus panels were commonly installed in homes from the 1950s to the early 1980s. Unlike modern panels that use a single main breaker to shut off power to the entire home, split bus panels are divided into two sections—an upper and a lower bus. The upper section typically powers large 240-volt appliances like dryers, water heaters, and ovens, while the lower section supplies lighting and standard outlets. What sets these panels apart is the lack of a single main breaker; instead, they rely on multiple breakers to control the entire panel. This design was allowed under the National Electrical Code (NEC) through what’s known as the “6-handle rule,” which permitted a home’s electrical system to be shut off using no more than six breakers.
Are Interlock Kits Compatible with Split Bus Panels?
As portable generator usage has grown, many homeowners with split bus panels have asked whether an interlock kit can be safely and legally installed on this type of panel. The answer is complex, largely because of the challenges these panels present. First and foremost, the absence of a main breaker makes it difficult to isolate utility power from generator power using a standard interlock kit. Most interlock kits are designed to lock out the main breaker when the generator breaker is in the “on” position, ensuring utility power and generator power cannot mix. With split bus panels, there is no main breaker to interlock against, which can create safety risks if not addressed properly.
The Dangers of Backfeeding Power
Another challenge is that the upper section of the panel feeds the lower section through one of the 240-volt breakers. If this breaker is left on during generator operation, it could allow generator power to backfeed into the utility lines, which is extremely dangerous and violates electrical code. Additionally, every split bus panel has a different configuration, meaning that a one-size-fits-all interlock kit solution isn’t practical. Because of this, installing an interlock on a split bus panel typically requires a custom-designed solution to ensure safe operation and compliance with code.
How InterlockKit.com Can Help
At InterlockKit.com, we’ve worked with many customers who own split bus panels, and we offer several solutions depending on the panel’s layout. In some cases, we can design a custom interlock kit that blocks the generator breaker against the breaker that feeds the lower bus. This setup ensures generator power cannot backfeed into the utility system. However, to remain compliant with the 6-handle rule, all breakers feeding power must be manually shut off when using a generator. This can be done safely if the panel is properly labeled and the homeowner is instructed on how to operate it.
When an Upgrade Might Be the Best Option
That said, we often recommend upgrading the panel entirely, especially if the split bus panel is over 40 years old or manufactured by companies like Zinsco or Federal Pacific, both of which are known for safety issues. Upgrading to a modern panel with a single main breaker allows for easier generator integration, better safety, and code compliance. Still, for those looking to keep their existing setup, we offer custom design services and hands-on guidance. Homeowners can send us photos of their panel, and our team will work with them to create a safe and effective interlock kit tailored to their configuration.
Final Thoughts on Split Bus Panels and Generator Backup
Understanding how the 6-handle rule applies to split bus panels is crucial when considering generator backup options. While these panels were once a code-compliant solution, modern electrical standards and the increased use of portable generators require more thoughtful planning. Whether you’re looking to add backup power to your home or upgrade to a safer panel, InterlockKit.com is here to help you find the right solution.
