Photograph of  photos of unsafe electrical circuit breaker burning up in the electric panel Circuit Breaker Reliability Tests
Standards, Procedures & Test Results for Residential Circuit Breakers

  • CIRCUIT BREAKER RELIABILITY TESTS - CONTENTS: about the safety & reliability of some brands of residential circuit breakers, circuit breaker testing according to UL-489 and breaker failures across several brands including FPE, Murray, Crouse-Hinds, BullDog Pushmatic
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Standards, UL-489 Test Procedures, Test Results for Some Residential Circuit Breakers

FPE electrical panel fire in progress (C) Dr. Jess Aronstein & Daniel Friedman

In 1985 as I (D Friedman) was leaving an ASHI home inspectors association meeting in Elmsford, New York, Tom Byrne, an old-timer gave me a tip:

"Watch out for those FPE Panels", Tom said, "They're no damn good."

"Could you be a bit more specific? What's wrong with them?" I asked.

"They're just no damn good. Warn people!" Tom grinned.

Until about 2011, electrical engineers, fire researchers, electricians, electrical inspectors and home inspectors in North America generally thought that there was one particularly-unreliable brand of circuit breaker installed in U.S. homes: FPE Stab-Lok circuit breakers and electrical panels installed over many decades.

[Click to enlarge any image]

These FPE or FPE-design circuit breakers sold under several brand names were notorious for failing to trip in response to an over-current.

See FPE HAZARD ARTICLES, STUDIES and see this SUMMARY of the FPE Stab-Lok® HAZARD for details.

The failure of a circuit breaker to trip when it should, that is to open or drop power to the electrical circuit it is supposed to be protecting risks fire and shock injury to buildings and their occupants.

Also unsafe if slightly more subtle, two-pole FPE breakers frequently jam internally so that even if the circuit breaker is switched to its OFF position, it may remain ON internally - risking a shocking surprise for someone who thinks she has turned off electrical power to the circuit before working on it.

No-Trip Failures of Older & "New" FEP FPE and UBI-FPE Circuit Breakers

Stab Lok circuit breaker test result summary (C) J AronsteinShown in the graph above/left, no-trip circuit breaker failure results for three FPE Stab-Lok® type circuit breakers tested by Aronstein & Lowry and reported by IEEE in 2011.

[Click to enlarge any image]

Those authors tested FEP breakers from the 1950's, FPE breakers produced from about 1960 to 1980, and UBI-brand Chinese-made "new replacement" circuit breakers for FPE panels collected from a condominium complex in 2004.

Aronstein & Lowry, in estimating fire losses associated with circuit breaker malfunction in the United states document the high failure rate of FPE circuit breakers (failure to trip in response to overcurrent when tested in accordance with UL Standard 489) comment in their paper's conclusion:

Incredibly, although factual information and test data as to the defective performance of FPE Stab-Lok® breakers has been available for at least a quarter of a century to those who would seek it out, there is no nationally respected electrical safety organization or authority that has taken the initiative to suggest publicly and in plain language that they be changed in the interest of fire safety. - Aronstein & Lowry (2011)

Failure Rates of Older Bryant, Frank Adams, Bulldog Pushmatic, Murray, Crouse Hinds Circuit Breakers

Circuit breaker test results for no-trip failures of Bryant, Fank Adams, BullDog Pushmatic, Murray & Crouse Hinds (C) D Carrier J Aronstein

Shown in the graph at above/left: Obsolete Circuit Breaker Testing by D. Carrier (2013) - un-published.

A common UL-489 test of circuit breakers exposes the breaker to 135% of its rated current. This is the "must-trip" current: at this level the circuit breaker switch must open to shut down the circuit. (Lower red line in the graph shown here).

For example, to test a 20-A circuit breaker at 135% of rated current we'd expose the breaker to a load of 27 Amps (1.35 x 20).

A second common circuit breaker test for breakers that did not open at 135% of rated current is to expose the breaker to 200% of rated current. In the chart shown here, Murray and Crouse Hinds breakers not only failed to open at 135% of rated current, they jammed there or at higher current.

A "jammed" circuit breaker will not open to turn off the circuit at any level of overcurrent whatsoever.

Beginning in 2011 and using both equipment and procedures provided by Jess Aronstein, an electrical engineer with long experience in electrical system failure research and testing, David Carrier, an electrical engineer in Poughkeepsie, New York, began testing additional brands of what he considered "obsolete" electrical circuit breaker brands collected from various homes.

While the total number of circuit breakers tested by Carrier remained a comparatively small sample (n=???), the results were striking, as you can see in the graph of test results shown just below.

Although the number of tests was limited, the pattern of test results is sufficiently clear and dramatic as to provide a compelling observation:

some electrical circuit breaker manufacturers, such as Bryant, quite apparently have got a sufficient grip on manufacturing, testing, and listing procedures for their products that the product performance in the field is very consistent, with virtually no failures-to-trip observed.

Yet other electrical circuit breaker manufacturers (Frank Adams, Bulldog Pushmatic, Murray, Crouse Hinds) produced circuit breakers whose performance, when independent tests were performed, showed dramatic failure rates.

We deliberately exclude from this data and from tests, electrical panels and circuit breakers that have been exposed to abnormal conditions such as flooding, wetting, or fires from other causes.


UBI FPE circuit breaker smoking under test at 400% of rated current (C) & J Aronstein 2017What should consumers, electricians, and building inspectors or home inspectors make of this situation?

Electricians who install electrical panels and circuit breakers, consumers who use them, and inspectors who examine them, can be expected to believe that in normal field situations,a circuit breaker that is exposed to over-current conditions as described in the most-widely-applied test standard in the U.S. (UL-489), the breaker will trip when it should. People expect that circuit breaker failures will occur both rarely and randomly.

What needs to be clearly stated is the user / purchaser expectation that the product on the market meets or exceeds the UL489 requirements, as certified by the listing label.

Making the picture a bit muddier is the fact that there are different degrees of severity of failure.

A few % over the limit calibration failure is not very serious, but a breaker that won't trip at all is a different level of hazard. - J. Aronstein to D. Friedman, private email, 2017/03/15

Photo above: a UBI-brand replacement FPE Stab-Lok circuit breaker smokes without tripping off under testing described at UBI FPE CIRCUIT BREAKER TEST RESULTS.

Ongoing tests of this contemporary replacement circuit breaker have to date found an overall failure rate of 45%. (n=265 in March 2017).

We do not have an electrical industry number telling us the expected percent of failure-to-trip problems among circuit breakers, but as Aronstein explains, consumers do expect that UL-listed circuit breakers, in normal, properly-functioning equipment that has not been damaged by some outside force (leaks, corrosion, fire, abuse, modification) will behave like this:

  1. The circuit breaker will fail to trip at 135% of rated load only in extremely rare cases
  2. Failures of circuit breakers to trip off when they should will be randomly distributed across the population of installed equipment

That is not the case.

Instead, the graphs and test data shown above and cited in the research below indicate that for some brands there are both a high no-trip failure rate and a sufficiently-consistent failure occurrence even among a relatively-small sample, that there is compelling evidence that the equipment is both unreliable and unsafe.

In our OPINION, changes in the electrical testing procedures permitted under UL-489 (UL now NRTL) underlies a deterioration in the quality of some electrical circuit breakers on the market.

Yhe fox is watching the henhouse - that is, manufacturers are permitted to conduct their own testing, monitored by a third party listing agency who in turn provides no test result information to the public. Some of them do a great job. Some, quite obviously, are not doing so well. In the Aronstein/Lowry data shown above, and as we explain in the bulleted items below,

In the United States, there is no person, no government agency, and no industry organization that has a stated responsibility to take action on this matter on behalf of public safety. - view of the authors

Conversely, the data also indicates that some circuit breaker manufacturers are producing a very reliable product.

The Bryant sample set comes from 5 different sources in four cities (Dallas, Armonk, Poughkeepsie, and Kingston). They are not from one lot and not likely to be from the same year.

You are right that [the sample set] small in number, but a tight distribution like this in a sample from 5 sources is a very strong indication that Bryant knew how to calibrate their breakers and their breakers do not deteriorate with age. - J. Aronstein to D. Friedman, private email, 2017/03/17  


The Authors:



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