Zinsco Breaker Panels - The Often Overlooked Hazard

Zinsco Breaker Panels – The Often Overlooked Hazard

Home inspectors and electricians, but few home owners and Realtors, are aware of the many safety issues attributed to some brands of breaker panels. Federal Pacific Electric (FPE) breaker panels are the most commonly talked about regarding safety issues, but that is not the only brand of breaker panel equipment prone to defects and failures. Zinsco is another brand of circuit breaker equipment that had some of its own unique issues that have lead to breakers not tripping when they should and sometimes melting and leading to arcing and house fires. Due to the Zinsco brand being purchased by Sylvania in the 1970s, Zinsco equipment is sometimes also labeled as “Zinsco-Sylvania” (and “Zinsco/Sylvania”) or even “GTE-Sylvania-Zinsco”.

The photo above shows a common Zinsco breaker panel with the front hinged cover open. These panels normally have a Zinsco sticker at the top and color-coded circuit breaker handles. Since a breaker panel is critical in helping to prevent a house fire, finding installed electrical equipment with a known history of defect or failure can be a serious issue warranting immediate attention.

Some of the same safety issues (such as breakers not tripping when warranted) attributed to FPE breaker panels are known to not be unique to that brand alone. Zinsco equipment also has some of these same serious issues. There is less technical data on Zinsco equipment available on the internet, so the failures with this brand of equipment aren’t as well publicized. Some electricians aren’t even aware of these serious hazards.

Dr. Jesse Aronstein, a well known expert on breaker panel failures, has spent considerable time and resources testing FPE equipment and documenting the serious issues with that equipment. He has also tested Zinsco equipment and found some very serious issues. Some of these issues pertain to bus bar plating deteriorating over time. A breaker panel’s bus bars are the metal pieces that circuit breakers clip onto and rely on a good connection for proper electrical power transfer. When bus bar plating is defective, these connections can be inadequate and may lead to overheating (the circuit breaker may literally melt) and fire. This issue is often impossible to see without removing all of the circuit breakers since the bus bar connections are blocked visually by the circuit breakers. Zinsco circuit breakers rely on a unique method of interfacing their breakers to the bus bars. Zinsco panels have 2 vertical parallel bus bars and the breakers simply clip onto the bus bars unlike almost all other circuit breaker designs. If a Zinsco panel isn’t full of breakers, the breakers can literally slide up and down the bus bars which can present other safety issues. Modern circuit breakers have a more reliable interface between bus bars and the breakers and must meet more stringent electrical safety standards. Other serious issues found with some Zinsco breakers pertained to them simply failing to trip when required.

Testing on Zinsco breakers performed by J. P. Simmons, a well known electrical expert known as “Mr. Electric”, indicated “that nearly 32% of the Zinsco circuit breakers tested to date failed to trip as required by the UL testing standard”. Also, “damage was found in 25% of the Zinsco/Sylvania panels that are checked”.

The above photo shows a melted Zinsco circuit breaker due to overheating.

This photo shows damage to the Zinsco panel’s bus bars. This is likely due to a bar plating issue and/or arcing due to a poor breaker/bar connection.

The above photos (courtesy of http://www.ismypanelsafe.com/) show melted Zinsco equipment including a charred bus bar.

A circuit breaker works by passing electrical current from the breaker panel’s bus bars to a branch circuit’s wiring. In essence, a circuit breaker isn’t really yet working until it detects excessive current and tripping (turning off the circuit). Electro-mechanical components inside the breaker should open the circuit if electrical current in excess of what the breaker is designed for occurs. Just because a circuit breaker has never tripped does not mean the breaker is working. The breaker’s internal tripping mechanism may have jammed; if/when this happens, the breaker’s handle may indicate that it is OFF, when it is really still ON and providing no over-current (overload) protection. This may lead to a huge amount of electrical current (an overload) to the circuit resulting in damage to whatever appliances are connected to that circuit, electrical shock, and/or fire. Without having a detailed evaluation of the breaker panel, it often can not be determined if a circuit breaker jam or overload situation has ever occurred. A breaker panel full of breakers may look perfectly fine on the surface, but what you can’t see from the front may be shocking.

I still occasionally find Zinsco breaker panels while inspecting homes. These breaker panels are well over 30 years old and do not meet modern safety standards. Zinsco equipment is now considered antiquated by most professionals in the electrical and home inspection industry. Due to the well-documented issues with Zinsco breaker panels and due to their age, when a home inspector finds such equipment, he should make his clients aware of their history and recommend full evaluation by a qualified electrician knowledgeable about Zinsco equipment. After the electrician evaluates the equipment, he should make a recommendation regarding the Zinsco breaker panel. In most situations that I’ve run across, after inspecting homes for over 15 years, electricians recommend replacement. Some newer Zinsco-style circuit breakers can be found (often made in China), yet even many of these newer Zinsco-style breakers are known to be defective and still don’t meet today’s standards.

Thank you to Dan Freidman, Dr. Jesse Aronstein, and J.P. Simmons for providing information for this article.

Good references for additional Zinsco breaker panel information can be found at:
https://inspectapedia.com/electric/Zinsco_Electrical_Panels.php

You may also find these related articles helpful:
Electrical Inspections Of Older Homes
Federal Pacific Electric (FPE) Breaker Panels

Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at matthew@thehomeinspectorsnotebook.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.