The main problem with Zinsco panels is they were produced with cheap bus bars (the part that conducts electricity to each breaker). While originally made with copper, in the 1960’s they were produced with plated aluminum. And instead of dedicated breaker “sockets”, Zinsco panels had a continuous bus bar to allow breakers to fit into position. This design led to two main problems:
As the breakers slid around and were adjusted over time, they scraped the coating off the aluminum bus bars, which caused oxidation and corrosion. This in turn led to poor connections with the breakers and higher risk of arcing at the point of contact with the bus bar. Unfortunately, the only way to inspect for poor breaker connections is to remove the breakers, which in turn contributes to the underlying and ongoing issue.
The second problem with this design is that since the breakers do not have a dedicated “socket”, they can sometimes slide or fall out! Some inspectors won’t even remove the panel cover if they come across a Zinsco panel for this reason! I’ve never had any fall out on me, but I’ve definitely run into my fair share of loose breakers.
In addition to these problems, Zinsco panels have also developed a reputation of failing to trip under load or only tripping slowly when required—both of which are dangerous situations and potential fire hazards. My parents had a Zinsco panel (installed in the mid 1960’s) where one phase would intermittently drop out for awhile and then come back on. Thankfully, their panel never started a fire before it was replaced, but that’s obviously not a good situation and potentially hazardous!
Bottom line: we always recommend replacing a Zinsco panel. “Zinsco” is a 4-letter word!
A Zinsco panel found at a recent inspection.