The deficiencies that became evident were serious enough to be considered both a fire and electrical shock risk. Panels were known to fail, while still conducting power. Here's the short version:
The overall design of the panel includes aluminum bus bars, which are subject to corrosion and overheating as energy demands increase. Once a breaker becomes taxed, subsequently melting to the bus bar, there is an inability of the breaker to adequately trip, and power continues to surge into the panel and associated downline circuits.
At this point, the panel is not able to be shut off manually and power is continuing to be supplied to the panel until the service can be terminated or wires melted.
It's important to note other branded electrical panels manufactured at approximately the same time as the Zinsco panels have not had the same failure rate to date. It has also been suggested that a listing by Underwriters Laboratories (UL) would never have been allowed had they been given correct data in testing.
Again, here are the major issues with Zinsco Panels:
- Certain components of the panel contain aluminum
- The connection between the breakers and bus bar is not solid
- Bus bar corrodes easily
- Breakers may appear to be off, yet internally the panel may be conducting power
If you know or suspect you may have a Zinsco brand panel, most experts in the field of electricity today recommend the panel be replaced. Even if an electrician tells you, he can replace parts, it would be wise to still opt for total panel replacement. The greatest reason being, the safety standards that were acceptable in the 60's and 70's are much more stringent today and would never be approved for use.
For a more detailed look at these issues and this product, click here.