Zinsco Q55 Miniature Circuit Breaker

The Zinsco Q55 is designed exclusively for use in legacy Zinsco load centers that accept Type Q plug-on circuit breakers. It is not compatible with modern panels from other manufacturers and requires the original Zinsco bus bar configuration.

Yes, the Zinsco Q55 is often cross-referenced as the Q155. Depending on the era of manufacture, it may also carry GTE Sylvania or Challenger branding, as those companies previously acquired the Zinsco product line.

The Q55 features standard lug terminals designed to accept 6 AWG to 4 AWG copper or aluminum wire. Ensure the connections are properly torqued to prevent arcing, which is a documented issue in older Zinsco panels.

The breaker uses a fixed LI (Long-Time, Instantaneous) trip profile. The thermal component provides a long-time delay to prevent nuisance tripping from temporary inrush currents, while the magnetic component offers instantaneous tripping to clear severe short circuits.

Yes, original Zinsco panels and breakers are considered obsolete and have documented safety issues, including failure to trip during overcurrent events and poor connections to the bus bar that can lead to arcing and fire hazards. Many electricians recommend a complete panel upgrade rather than installing replacement breakers.