A split-bus electric panel, also known as a split-bus distribution panel, is a type of electrical panel configuration that was commonly used in residential electrical installations in the past. It consists of multiple circuit breakers organized into two sections or buses, hence the name "split-bus."
The primary characteristic of a split-bus panel is that it does not have a single main circuit breaker to disconnect power to the entire panel. Instead, it divides the electrical load into two sections: the "main" section and the "branch" section. The main section usually contains a group of circuit breakers that control large appliances and high-demand circuits, such as electric water heaters, electric furnaces, or air conditioning units. The branch section contains circuit breakers that control individual branch circuits throughout the house, including lighting, outlets, and smaller appliances.
In a split-bus panel configuration, the main section is typically fed directly from the service entrance cable without passing through a main circuit breaker. Instead, each circuit in the main section has its own circuit breaker that can be individually turned off or on. The branch section of the panel is usually connected to a smaller circuit breaker, referred to as a "lighting main" or "lighting section breaker." When this breaker is turned off, it shuts off power to the entire branch section.
Split-bus panels were commonly used in older homes built between the 1950s and 1980s. However, they have fallen out of favor and are no longer installed in modern residential construction due to changes in electrical code requirements and safety concerns. The National Electrical Code (NEC) now requires a main circuit breaker to be present in residential electrical panels, providing a single point of disconnection for the entire panel.
It's important to note that if you have a split-bus panel in your home, it's advisable to consult with a licensed electrician to evaluate its condition and determine if an upgrade or replacement is necessary to ensure compliance with current electrical codes and safety standards.