UBI FPE circuit breaker smoking under test at 400% of rated current (C) & J Aronstein 2017Electrical Circuit Breaker Failures & Failure Test Results
Independent expert tests find high failure rates among several brands of circuit breaker

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Electrical Circuit Breaker Burns, Fails to Trip, Continues to Conduct Power:

Circuit breaker performance data & field failure reports. This document demonstrates detection and fire risks of a bad electrical circuit breaker which burned, failed to trip, and remained live in the electric panel.

Page top photo of a UBI circuit breaker overheating and smoking under testing, courtesy of Dr. Jess Aronstein.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Electrical Circuit Breaker Failures: Testing, Failure Rates, Research, Detection by Simple Visual Inspection

New circuit breaker failure rates (C) Jess Aronstein 2017Failure Rates of New Off-the-Shelf Circuit Breakers

A 2017 study by Dr. Jess Aronstein found significant no-trip failures among three brands of circuit breakers (UBI, Siemens/Murray)* and essentially no significant failure rates among three other brands of circuit breakers:

[Click to enlarge any image]

Above: test results for common brands of new circuit breakers as of 13 October 2017. [Click to enlarge any image]

Dr. Aronstein, an independent electrical engineer who has performed testing for various government and private agencies notes that the UBI-brand circuit breakers were the worst performing of the group tested.

Aronstein commented (May 2017):

The UBIs are the worst of the lot, and they are the only ones other than FPE that have shown a tendency for the 2-pole breakers to jam.

The surprise was that the Siemens and Murray (identical breakers with different paper labels on them) are not meeting the UL spec.

Next problem is that although many people and organizations have the authority to do something about it, nobody has the responsibility to take any action.

Failure Rates of Used Circuit Breakers

Failure rates for brands of used circuit breakers (C) J Aronstein

[Click to enlarge any image] Source of the table above: personal email, Dr. Jess Aronstein to Daniel Friedman, 2017/05/11 & 2017/10/19.

Above, circuit breaker failure test results for these circuit breaker brands (left to right): Bryant/Westinghouse, Square-D, Bulldog (Pushmatic), GE, ITE, Zinsco, FPE (Stab-Lok), UBI (replacement breakers for several panels), Murray, Crouse Hinds.

This failure data test report is as of 29 September 2017 and includes tests performed by David W. Carrier and Jess Aronstein between 2013 and 2017.

At MOLDED CASE CIRCUIT BREAKERS - SOME HOLES IN THE ELECTRICAL SAFETY NET [PDF] you will find the latest research by these authors in an IEEE paper to be published in 2018.

Notes on Aronstein's chart indicate:

1. Data points on this chart are 1-pole breakers and worst case poles of 2-pole breakers.

2. These used [circuit] breakers are field samples that were removed from buildings during upgrades or renovations.

3. FPE [circuit breaker failure test result] data is representative of 3000 breakers that have been tested.

Contribute UBI (Connecticut Electric) and Zinsco Brand Circuit Breakers for Independent Testing

Dr. Aronstein would like to obtain and test UBI (Connecticut Electric) Zinsco type replacement breakers that might be in your electrical panel. They are usually grey in color, and might have been installed as replacements or when new circuits were added.

To date I have tested only four of the UBI-Z types, and all four failed to perform properly. If you have any of the UBI-Z breakers, please send them to:

Jesse Aronstein, Ph.D., P.E.
909 Londonderry Ct.
Schenectady, NY 12309

Noting that you found this request at this web page:

Articles describing other in-service or "used" circuit breaker brands are included in this article below at CIRCUIT BREAKER FAILURE RESEARCH.

The circuit breaker test standard, UL-489, is described and cited at UBI FPE CIRCUIT BREAKER TEST RESULTS where you will also find additional test results that included both new and used UBI circuit breakers.

Reader Question:where to find performance data on various circuit breakers

Square D Channenter breaker substitute failure (Nov 20, 2014) Steve L said:

I'm looking to replace an old panel for a variety of reasons. I'm wondering where I can find recent performance/fire/etc data on various brands of circuit breakers so I can form an idea of which brands to favor or avoid in selecting a new panel.

I'm also curious about which brands have the best performing (C)AFCI and GFCI breakers since most searches are flooded with the problems that all brands had in the early days of AFCI. Is there are good source for this information? Many thanks!

This question was originally posted at ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR


Steve you ask a fair question.

From speaking with industry experts over several decades it's apparent that most of the circuit breakers and panels by major equipment manufacturers perform very well, with failure-rates (as in fail-to-trip in response to an overcurrent) are at a very small fraction - well under 1 per-cent. The highest "generic" opinion about circuit breaker failure to trip rates that I have found was reported at 4% as anecdotal evidence by Koty (un-dated, retrieved 2015, cited below).

Our OPINION is that in most installations conventional residential circuit breakers from most manufacturers almost never fail to trip when they should - certainly that is the expectation of consumers.

Illustrated above, a Classified circuit breaker (burned, damaged) discussed at Classified CIRCUIT BREAKER WARNING.

A few brands of older equipment described in articles at InspectApedia such as Challenger, FPE-Stab-Lok, Zinsco have notably higher problem and failure rates, in some cases as high as 60% no-trip rates. That's a failure rate around 600 times worse than what we expect in the industry.

We are now in the 4th generation of AFCI devices - so I would not tar current brands with more historical issues, but I agree that nuisance tripping, particularly on AFCI's has been a reported problem yet to be fully addressed.

See AFCIs ARC FAULT CIRCUIT INTERRUPTERS for examples. That article includes a link to an IEEE article on what we can and cannot expect from AFCIs and how they perform.

David Carrie, a New York electrical engineer briefly continued Jess Aronstein's work on testing circuit breaker performance independently of work supported by manufacturers but regrettably, although he reported (to me privately) that some current circuit breaker brands seemed to have higher no-trip rates than the industry average, he did not complete nor report that research publicly.

By 2014 it appeared that David had moved on to other projects. Dr. Aronstein took up that task once again and in 2017 we include some of his recent test results here. See UBI FPE CIRCUIT BREAKER TEST RESULTS.

Research on Electrical Circuit Breaker Performance & Failure Rates

Photograph of this recalled Square D GFCI circuit breakerRecent research citations on circuit breaker performance and breaker failure rates such as no-trip or failure to trip in response to an over-current.

Other critical electrical system failures that are directly or closely related to individual circuit breaker brands, models, or wiring practices are explained and photo-documented at the live-linked articles just above.

Warning about Do-It-Yourself Circuit Breaker Testing

Watch out: circuit breaker trip testing such as described both by Koty (op.cit). and by vendors of clamp-on ammeters is a dangerous proposal, especially if the breakes and equipment are installed in the building they are intended to serve. For example testing a circuit breaker in-situ in a home by putting a deliberate overload on the circuit risks setting the building on fire.

Other do it yourself or homeowner circuit breaker testing risks include inaccurate test results, conducting an improper test that does not properly assure that the circuit breaker will perform correctly under varying conditions of load, time, and environments, reporting as "safe" a breaker that is in fact not compliant with ANSI C37 nor UL standards such as UL 489 or other pertinent circuit breaker testing standards, and worst: some problem brands such as FPE experience an increased fail-to-trip rate (fail to open in response to an over current) after the breaker has been "exercised" either by switching it on and off or by exposing it to an overcurrent.

We do not recommend circuit-breaker testing by homeowners, electricians, nor in-situ testing of circuit breakers unless conducted by an expert.

Full View of Electrical Panel with a Burned Circuit Breaker

You don't need a VOM or digital volt meter to see bad burn ups like the circuit breaker failures shown later in this article  but this failure is a strong recommendation for use of digital multimeters or simple neon testers to confirm that circuit breakers really do turn off the power.

On opening the panel, arcing and burn marks were obvious. Note the black stains along the left side of the right-hand bus bar above the highest breaker in the panel.

Note also the corrosion present at the neutral bus and bus bar connector at the panel bottom right corner. This panel was in a wet utility basement of an old house in New York state.

However it did not appear that moisture in the panel from basement conditions was the root cause of overheating and damage. There was not general corrosion throughout the panel. The panel itself was relatively new, less than ten years old.

A Look at the Electrical Panel Center

A look at the center of the panel shows pieces of circuit breaker plastic and other debris that was obviously a product of arcing and burning at one of the circuit breakers.



Close up View of the Electrical Panel Center

A closer look at the same area shows a piece of one of the right-hand breakers sitting atop the lower breaker on the left. Notice the red and white corroded material at the lower right corner of the top breaker. J. Aronstein suggests that overheating in the breaker burned off zinc or other anti-corrosive plating leading to bleed-out of rust particles.

Other breakers in the panel, presumably of the same age, did not show these visual indications of damage.

Burned, arced breaker still in place, still "live"

Finally, shifting the angle and getting some better light on the subject one could see that the lower of the uppermost two breakers in the panel right side had burned badly where it was connected to the aluminum bus of the panel.

It was remarkable that despite severe damage to the breaker and panel bus, the breaker was still conducting current to the circuit connected to it.

During a home inspection inspectors should not touch equipment like this. Using a TIF Instruments Tic Tracer it was possible to confirm live electrical power at various points. Of course, what's called-for is an immediate repair which most likely requires replacement of the bus assembly and breakers if not the whole panel.

Home inspectors are not forensic engineers, but it appears obvious to anyone looking at this equipment in-situ that overheating at the connection of the breaker to the panel bus must have led to arcing, breaker damage, and thus creation of an unsafe condition in which there is very likely no overcurrent protection being provided by this equipment.

You don't need a VOM or digital volt meter to see bad burn ups like this but this failure is a strong recommendation for use of digital multimeters or simple neon testers to confirm that circuit breakers really do turn off the power.

Contributing Authors


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