Circuit breakers are designed to be a safety feature in an electrical system. When a short circuit or overload condition develops, the breaker "trips," disabling the circuit. Most circuit breakers are housed in the main electrical panel, called the breaker panel or box. These boxes are manufactured by various companies. Unfortunately, companies are not willing to make their breakers interchangeable. For example, a Square D breaker will not fit into a Federal Pacific breaker box. Because of this fact, some aftermarket breaker manufacturers design breakers to fit each manufacturer's box.

For a panel manufactured by Challenger, the Connecticut Electric breakers will fit. These are types UBITBC and UBITBA . Also, the Cutler Hammer BR breakers will fit. As with all panels, the original equipment manufacturer's (OEM) breakers are designed to fit the panel.

For the Pushmatic box, breakers from Pushmatic and Connecticut Electric will fit. The Connecticut Electric breakers are type UBIP.

Westinghouse/Bryant breakers will fit the panels. Cutler Hammer and Connecticut Electric breakers will also fit. The Cutler Hammer BR series are designed to fit, as are the Connecticut Electric UBITBC series.

The Connecticut Electric Type UBIZ series of breakers will fit Zinsco panels. These breakers are available in a variety of amperages, and it is up to your electrician to determine which size breaker is needed for each branch circuit.