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.

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

Failure 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.

Electrical Wire Failures: Causes vs Time: Bathtub Curve

A 1980 US CPSC study found that aging electrical systems are a factor in the occurrence of electrical fires in homes, an observation confirmed separately by Aronstein in explaining aluminum wiring hazards in what Aronstein calls the "bathtub curve" that maps failure rates over time.

Failures occur early in the wiring system life due to original installation defects and then failures occur again at an increased rate late in the installation's life as the wiring ages and as it has been exposed to the vagaries of use over decades. This bathtub curve of failure rates is illustrated

at ALUMINUM WIRING SAFETY ASSESSMENT.

Older homes often have electrical receptacles and fixtures that are ungrounded, and many local codes do not require that they be rewired so they're grounded. Still, grounding is worth adding to your system because it adds protection against electrical shock.

But Dini points out that "... most of the hazardous conditions found in the 30 houses [studied] could be attributed to a lack of compliance with a specific code requirement". (Dini 2008).

Failure Rates of Used Circuit Breakers

[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 InspectApedia.com web page: https://inspectapedia.com/electric/Circuit_Breaker_Failures.php

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

(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

Reply:

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 (undated, 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.

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 breakers 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 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.

Research on Electrical Circuit Breaker Performance & Failure Rates

Recent research citations on circuit breaker performance and breaker failure rates such as no-trip or failure to trip in response to an over-current.

• ALUMINUM WIRING HAZARDS & REPAIRS [Web article] aluminum electrical wiring can cause fires without tripping a circuit breaker
• AFCIs ARC FAULT CIRCUIT INTERRUPTERS [Web article] nuisance tripping
• Aronstein, Jesse. "Temperature Sensitivity of Residential Molded Case Circuit Breakers." IEEE Access 7 (2019): 38714-38720.
  
  This report can can be download as a PDF from IEEE at no cost at the following
  
  URL: https://ieeexplore.ieee.org/document/8669748 but may not be reproduced without IEEE permission - Ed.
  
  ABSTRACT
  
  The experimental results are presented for minimum trip current as a function of temperature for residential circuit breakers. These are often installed in enclosures that are exposed to seasonal temperature extremes.
  
  The trip current of these thermally actuated breakers is inversely related to temperature. The relationship is shown to be linear and it varies as much as 2:1 between brands.
  
  The trip current at extremely high and low temperatures can be estimated. At low outside ambient temperature the worst case 15A breakers will not trip at 25 A, which would be the current load of two 1500W portable heaters plugged into the same 15 A circuit.
  
  The diminished overcurrent protection at low temperature may be a factor that contributes to the elevated incidence of residential electrical fires during winter months.
• Aronstein, Jess ¹, (Life Senior Member, IEEE), & David W. Carrier ² MOLDED CASE CIRCUIT BREAKERS - SOME HOLES IN THE ELECTRICAL SAFETY NET [PDF]
  
  Received December 4, 2017, accepted January 24, 2018, date of publication February 7, 2018, date of current version March 15, 2018. Digital Object Identifier 10.1109/ACCESS.2018.2803298
  1 Consulting Engineer, Schenectady, NY 12309, USA, 2 SUNY Dutchess Community College, Poughkeepsie, NY 12601, USA, Corresponding author: Jesse Aronstein ([email protected])
  
  This paper is also available at no charge at the IEEE Explore website. It can be accessed for online reading at: http://ieeexplore.ieee.org/document/8283732/

and can be downloaded directly from IEEE at http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8283732

Abstract:
Test results presented in this paper demonstrate that some brands of residential molded case circuit breakers do not operate properly within the limits specifieded by the applicable standard. The samples tested are both used, from homes, and new, purchased at retail sources. The minimum trip current is determined for each breaker.

The test procedure encompasses the basic overload trip requirements of the applicable standard. Breakers that do not open the circuit at or below 135% of rated current fail to meet the requirements of the standard. Test results vary substantially from brand to brand.

The best brands are essentially failure free.

The failure rate of the worst-case brands is in the order of 50% for both used breakers from homes and new breakers recently purchased. Some samples, primarily multi-pole breakers, do not open the circuit at any level of applied current.

Failure of a circuit breaker in a home to operate properly when required poses an increased risk of fire and injury.
• Aronstein, Jesse, and Richard Lowry. ESTIMATING FIRE LOSSES ASSOCIATED WITH FPE STAB-LOK® CIRCUIT BREAKER MALFUNCTION [PDF] In Electrical Safety Workshop (ESW), 2011 IEEE IAS, pp. 1-7. IEEE, 2011. - retrieved 2021/06/25 original source: http://www.fpe-info.org/estimating_fire_losses_due_to_fpe_malfinction.pdf
  Abstract:
  
  A method is presented for connecting small branch circuit breaker functional test data to statistical fire loss data.
  
  Test results are presented for field samples of a particular line of circuit breakers that have an abnormally high defect level.
  
  The test results are then utilized in combination with available electrical fire statistics to estimate the annual number of fires and consequent injuries, deaths, and monetary loss associated with the defective breakers.
  
  An estimate is then made of the reduction of injury and loss that can be achieved by encouraging replacement of the defective breakers. The role of the electrical safety community in promoting replacement of the defective breakers is discussed.
• "Failure Analysis of Residential Circuit Breaker Panel", Wright-Malta Corp., (by J. Aronstein, for U.S. Consumer product Safety Commission, Project #CPSC-C-81-1455), May 20, 1982 (Contains failure analysis of FPE Stab-Lok® panel that ignited, due to failure of buss-bar interconnections in the backside of
  the panel.)
• "Final Report: Calibration and Condition Tests of Molded Case Circuit Breakers", Wright-Malta Corp., (by J. Aronstein, for U.S. Consumer product Safety Commission, Project #CPSC-C-81-1429), December 30, 1982 (Extensive calibration and functional testing of FPE breakers. Substantial percent failures
  to trip on overload.).
• "Status Report - Evaluation of Residential Molded Case Circuit Breakers", Wright-Malta Corp., (by J. Aronstein, for U.S. Consumer product Safety Commission, Project #CPSC-C-81-1455), August 10, 1982 (Contains analysis of mechanism of failure of FPE two-pole Stab-Lok® breakers.)
• "Phase II Report, Evaluation of Residential Molded Case Circuit Breakers", Wright-Malta Corp., (by J. Aronstein, for U.S. Consumer product Safety Commission, Project #CPSC-C-81-1455), March 10, 1984 (Contains experimental analysis of materials, construction, and performance of molded case circuit breakers, including FPE.)
  
  and citing: Partial Summary Judgment decision dated 8/15/02 by Judge Bryan D. Garruto, J.S.C., Superior Court of New Jersey, Law Division: Middlesex County, Docket No. L-2904-97
• Anderson, J. G. P., N. S. Ellis, F. Mason, R. G. Noble, L. H. Orton, M. P. Reece, and J. G. Steel. "Synthetic testing of ac circuit breakers. Part 1: Methods of testing and relative severity." In Proceedings of the Institution of Electrical Engineers, vol. 113, no. 4, pp. 611-621. IET Digital Library, 1966.
• ANSI C37, 50-2012, Low-Voltage AC Power Circuit Breakers Used in Enclosures ù Test Procedures, ANSI Attn: Customer Service Department 25 W 43rd Street, 4th Floor New York, NY, 10036, USA, E-mail: [email protected] Phone: 212.642.4980, Website: http://webstore.ansi.org/
  Abstract:
  
  Covers the test procedures for enclosed low-voltage ac power circuit breakers as follows:
  
  a) Stationary or drawout circuit breakers of two-, three-, or four-pole construction, with one or more rated maximum voltages of 635 V (600 for units incorporating fuses), 508 V, and 254 V for application on systems having nominal voltages of 600, 480, and 240 V;
  
  b) Unfused or fused type circuit breakers;
  
  c) Manually operated or power operated circuit breakers with or without electromechanical or solid-state trip devices;
  
  d) Fused drawouts consisting of current-limiting fuses in a drawout assembly intended to be connected in series with a low-voltage ac power circuit breaker to form a non-integrally fused circuit breaker. This document applies to both integrally and non-integrally fused circuit breakers.
• Babrauskas, Vytenis, HOW DO ELECTRICAL WIRING FAULTS LEAD to STRUCTURE IGNITIONS [PDF file downloaded 2017/03/15] In Proc. Fire and Materials 2001 Conf, pp. 39-51. 2001.
  Abstract:
  
  A sizable fraction of ignitions of structures are due to electrical faults associated with wiring or with wiring devices.
  
  Surprisingly, the modes in which electrical faults progress to ignitions of structure have not been extensively studied. This paper reviews the known, published information on this topic and then to point out areas where further research is needed.
  
  The focus is solely on single-phase, 120/240 V distribution systems. It is concluded that systematic research has been inordinately scarce on this topic, and that much of the research that does exists is only available in Japanese.
• Billinton, Roy, Ronald Norman Allan, and Ronald N. Allan. Reliability evaluation of power systems. Vol. 2. New York: Plenum press, 1984.
• Braun, A. "Validity of Unit Testing on Circuit-Breakers Exhibiting Statistically Varying Breaking Capacity." Power Apparatus and Systems, IEEE Transactions on 3 (1972): 791-797.
• BRYANT ELECTRICAL PANEL AGE & PROPERTIES
• CHALLENGER ELECTRIC PANELS [Web article] Challenger Electric panel history, field reports of overheating bus bars & circuit breakers, history, relationship to FPE Stab-Lok equipment
• Classified CIRCUIT BREAKER WARNING [Web article] from Square-D who explains the company's opposition to use of interchangeable or substitute circuit breakers
• COUNTERFEIT SQUARE-D CIRCUIT BREAKER RECALL [Web article] CPSC Notices Regarding two circuit breaker products: Recalled Square-D Circuit GFCI Breakers and Counterfeit Square-D Breakers.
• CPSC FPE FAILURE DATA 1982 [Web article] FPE Stab-Lok circuit breaker failure rate data: This article presents research data demonstrating the failure rates of Federal Pacific Electric Stab-Lok® circuit breakers. web article at InspectApedia.com
• CUTLER HAMMER ELECTRICAL PANELS [Web article] photographs of older Cutler Hammer electrical panel using a copper bus & comments on its condition. Separate field report of a Cutler Hammer Electrical Panel Fire, Photos, with speculation about possible causes.
• Dehghanian, Payman, and Mladen Kezunovic. "Cost/benefit analysis for circuit breaker maintenance planning and scheduling." In North American Power Symposium (NAPS), 2013, pp. 1-6. IEEE, 2013.
  Abstract:
  
  Maintenance planning and scheduling of circuit breakers (CBs) always involves the cost and benefit analysis. This paper introduces a new framework for cost/benefit assessments using condition-based monitoring data. The signals monitored at the CB control circuit are first utilized to determine the CB deterioration status.
  
  This information is used to decide which type of maintenance, e.g., minor, major, or replacement, needs to be practiced for different CBs. System wide analysis is then performed to assess the cost benefits of the maintenance by calculating the costs imposed to the system in the case of CB mal-operation.
  
  A new benefit to cost ratio (BCR) index is introduced to deal with the CB maintenance prioritization process.
  
  The proposed approach is implemented on a breaker-and-a-half substation configuration and the results demonstrate the applicability of the presented framework in real world scenarios.
• Dini, David A RESIDENTIAL ELECTRICAL SYSTEM AGING RESEARCH PROJECT [PDF] Fire Protection Research Foundation, Quincy, MA (2008). Retrieved 6/6/2010, original source: http://ul.com/global/documents/corporate/aboutul/publications/newsletters/thecodeauthority/tca_issue_2_2008.pdf
  and
  The Residential Electrical System Aging Research Project done for NFPA/FPRF is available in its entirety at this site, http://ewh.ieee.org/cmte/pses/ffat/support/RESAReport.pdf
• Emanuel, A. E., and John W. Dougherty. "Sensitive ground fault interrupter performance in the presence of direct current." Power Delivery, IEEE Transactions on 1, no. 1 (1986): 111-117.
• FEDERAL NOARK PANEL FAQs [Web article]
• FEDERAL PACIFIC FPE HAZARDS [Web article] fire and shock hazards associated with Federal Pacific Electric Stab-Lok® circuit breakers and service panels
• FPE Stab-Lok® : FIRES WAITING TO HAPPEN [Web article] description of the Latent Fire, Shock Hazards of FPE Stab-Lok® Equipment also may show up in CHALLENGER ELECTRIC PANELS brand electrical panels.
• FEDERAL PIONEER CIRCUIT BREAKER RECALL [Web article] Recall of Federal Pioneer NC015 and NC015CP Circuit Breakers in Canada
• FEDERAL PIONEER PANEL SAFETY - 2023 update & prior research on on Canadian FP breaker and panel failures confirms a similar failure rate as U.S.
• Fu, Xing, Xiaorui Wang, and Charles Lefurgy. "How much power oversubscription is safe and allowed in data centers." In Proceedings of the 8th ACM international conference on Autonomic computing, pp. 21-30. ACM, 2011.
  Abstract:
  
  Data centers attempt to maximize return on investment by achieving high levels of utilization. This means deploying the maximum number of servers possible within existing power supply capabilities. Therefore, a key problem is determining how many servers can be safely accommodated.
  
  Recently, a variety of power capping solutions have been proposed to safely allow oversubscription of available power, but they conservatively assume that peak power should never exceed the rated power distribution equipment capacity. Hence, the open question is: how much power oversubscription is indeed safe? In this paper, we focus on data center branch circuits and systematically study the tripping characteristics of their circuit breakers (CBs).
  
  Our results on a physical testbed show that instantaneous violations of the rated CB power limit are not necessarily fatal because CBs are designed to sustain a certain amount of power overload.
  
  Whether a CB trips or not depends primarily on the transient behaviors of a power overload, such as the magnitude and duration time, as well as ambient temperature. We propose two adaptive power control strategies that utilize the CB tripping characteristics to aggressively optimize the system performance without causing the CB to trip.
  
  Our extensive hardware results with SPEC CPU2006, SPECJBB, and LINPACK benchmarks show that the proposed CB-aware power control solutions achieve 38%, 75%, and 68% better average performance, respectively, than a state-of-the-art baseline.
  
  A key contribution of our work is to provide a practical upper bound of the server power oversubscription allowed on branch circuits. As a result, our solutions allow a data center to host three times more servers than traditional static power provisioning schemes and 54% more servers than the current power capping practice.
• Gregory, George D., and Gary W. Scott. "The arc-fault circuit interrupter, an emerging product." In Industrial and Commercial Power Systems Technical Conference, 1998 IEEE, pp. 48-55. IEEE, 1998.
• Hall, William M., Gary Donner, Banafsheh Kalhori, George D. Gregory, John Gardner, and Matt Samojeden. "A user guide to the selection, application, testing and life expectancy of molded case circuit breakers." In Petroleum and Chemical Industry Conference, 1995. Record of Conference Papers., Industry Applications Society 42nd Annual, pp. 65-75. IEEE, 1995.
  Abstract:
  A working group representing the PCIC and I&CPS and manufacturers are preparing a guide to give users information for the correct selection, application, testing, and life expectancy of molded case circuit breakers. This paper is intended to be a tutorial type presentation. This is the first phase of the solution to understanding the present method of rating molded case circuit breakers.
• Heunis, Schalk W., and Ron Herman. "A probabilistic model for residential consumer loads." Power Systems, IEEE Transactions on 17, no. 3 (2002): 621-625.
• IEEE Standards Collection, C37 -- Circuit Breakers, Switchgear, Substations, and Fuses, 1995 Edition, The Institute for Electrical and Electronics Engineers, Inc. New York, NY: IEEE
• Kimball, Jonathan, and Jordan Henry. "Compatibility between GFCI breakers and household adjustable speed drives." In Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE, pp. 517-520. IEEE, 2009.
• Koty, Ken, "Testing and Exercising Branch Circuit Breakers", web page article, Website: http://www.pducables.com/ Email: [email protected], retrieved 3 April 2015, original source http://www.pducables.com/TestingandExercisingBranchCircuitBreakers.htm
  Excerpt:
  I found from my years of experience of testing branch circuit breakers installed in our data centers, between overloaded branch circuits and direct shorts, about a 4% failure rate. Even though 4% may not seem like a large percentage, in most data centers, 4% of the thousands of circuit breakers used can still place a significant number of servers at risk.
• Lee, Jaebok, Sughun Chang, Sungho Myung, and Yuengue Cho. "Transient false tripping characteristic analysis of ground fault circuit interrupter." In Power System Technology, 2004. PowerCon 2004. 2004 International Conference on, vol. 1, pp. 522-526. IEEE, 2004.
• Lindquist, T. M., Lina Bertling, and Roland Eriksson. "Circuit breaker failure data and reliability modelling." IET generation, transmission & distribution 2, no. 6 (2008): 813-820.
  Abstract:
  
  The results from an extensive study of SF6 and minimum-oil circuit breaker failures in the Swedish and Finnish transmission systems are presented.
  
  The study includes 1546 breakers with a total operating history of 16 384 years. In the study, a detailed analysis of a specific SF6 type of breaker revealed which parts caused the failures and an estimation of their hazard rates was made.
  
  A model of complete reliability for this type of breaker is presented, illustrated by presenting the operating and maintenance history of a shunt reactor breaker in the Swedish transmission system.
• Lippert, Kevin J., and T. Domitrovich. "AFCIs-From a standards perspective." In Electrical Safety Workshop (ESW), 2013 IEEE IAS, pp. 57-61. IEEE, 2013
• MURRAY CIRCUIT BREAKER HAZARDS [ Web article ]
• MURRAY SIEMENS Recall [PDF]
• Mili, Lamine, Q. Qiu, and Arun G. Phadke. "Risk assessment of catastrophic failures in electric power systems." International Journal of Critical Infrastructures 1, no. 1 (2004): 38-63.
  Abstract:
  
  The declining reliability of the US electric power system is raising major concerns among both politicians and power engineers in the USA. One of the reasons put forward by the North Electric Reliability Council (NERC) is the detrimental role played by the protection systems during large disturbances, which tend to help the perturbations to propagate through over-tripping of fault free system components due to hidden failures.
  
  It turns out that the present practice in power transmission planning and online security analysis is to neglect the impact of the protection systems. In addition, the aim is to mitigate the vulnerability of the system to the loss of a single piece of equipment only by carrying out an N-1 security analysis. Consequently, the risk of cascading failures leading to blackouts and brownouts is neither assessed nor managed.
  
  This paper describes methodologies together with algorithms that assess the conditional risk of catastrophic failures in electric power networks due to hidden failures in protection systems. A catastrophic failure, defined as one that results in the outage of a sizable amount of load, may be caused by dynamic instabilities in the system or exhaustion of the reserves in transmission due to a sequence of line tripping leading to voltage collapse.
  
  Only the latter case is being considered. The aim of these algorithms is to identify the weak links in the systems, which are defined as those branches of the network whose tripping due to a fault lead to the highest probabilities of a catastrophic failure. The proposed methods are demonstrated on a 7-bus and a 61-bus system.
• Natti, Satish, Panida Jirutitijaroen, Mladen Kezunovic, and Chanan Singh. "Circuit breaker and transformer inspection and maintenance: probabilistic models." In Probabilistic Methods Applied to Power Systems, 2004 International Conference on, pp. 1003-1008. IEEE, 2004.
• NEMA Standards Publication AB 4, National Electrical Manufacturers Association, Washington DC 20037: NEMA
• Pahl, Birger, Thomas J. Schöpf, Xin Zhou, and Engelbert Hetzmannseder. "Arc faults in residential electrical systems." VDE-Fachbericht-Kontaktverhalten und Schalten (2009).
• PRIVATE BRAND/ EMI FPE PANELS [Web article]
• PUSHMATIC - BULLDOG PANELS [Web article] Pushmatic Bulldog Circuit Breaker & Electrical Panel Possible Safety & Operating Concerns
• Rusek, Bartosz, Gerd Balzer, Martin Holstein, and Max-Steffen Claessens. "Timings of high voltage circuit-breaker." Electric Power Systems Research 78, no. 12 (2008): 2011-2016.
• SQUARE-D COUNTERFEIT BREAKER RECALL [Web article]
• Schlabbach, Jiirgen, and T. Berka. "Reliability-centred maintenance of MV circuit-breakers." In Power Tech Proceedings, 2001 IEEE Porto, vol. 4, pp. 5-pp. IEEE, 2001.
• Schneider Electric, "ANSI® C37 Standard and UL® 489 Standard Comparison", Schneider Electric, Data Bulletin No. 0613DB9902, June 1999, Cedar Rapids IA, USA, retrieved 3 Apr 2015, original source: http://static.schneider-electric.us/docs/Circuit%20Protection
  /Insulated%20Case%20Circuit%20Breakers/0613DB9902.pdf
  Excerpts:
  
  The scope of the UL 489 Molded Case Circuit Breaker Standard includes miniature circuit breakers (MCBs), molded case circuit breakers (MCCBs) and insulated case circuit breakers (ICCBs).
  
  These circuit breakers are typically rated 10–6000 A and up to 600 Vac and 500 Vdc. Circuit breakers designed and tested to this standard typically exhibit the following characteristics:
  Sealed molded case
  Little or no maintenance
  No user replaceable parts
  Good performance and reliability
  Long service life
  ...
  The scope of the ANSI C37 Low Voltage Power Circuit Breaker Standard includes 2- or 3-pole stationary and drawout circuit breakers. The specifications of these circuit breakers are 254, 508 or 635 Vac maximum, fused or unfused, and manually- or power-operated with or without electromechanical or electronic trip units. These circuit breakers typically exhibit the following characteristics:
  Iron frame—older designs are open, newer designs are closed
  Maintainable for long service life
  Most parts can be replaced in the field
  High performance and reliability
  High maintenance costs
  ...
  The main construction differences between UL 489 Listed and ANSI C37 Certified circuit breakers are maintainability, ampere interrupting ratings (AIRs), heat rise and endurance. These construction differences result from the design and test philosophies outlined above.
  
  These differences will be discussed under Performance Testing. UL 489 Listed circuit breakers are sealed and require no maintenance for a long service life. ANSI C37 Certified circuit breakers typically require maintenance for long life and have been designed with an open case to facilitate maintenance.
• Sprague, Michael, J., "Service-Life Evaluations of Low-Voltage Power Circuit Breakes and Molded-Case Circuit Breakers", Michael J Sprague Member, IEEE Cutler-Hammer, Inc. 130 Commonwealth Drive Warrendale, PA 15086 USA, retrieved 3 April 2015, original source: http://www.eaton.eu/ecm/groups/public/@pub
  /@electrical/documents/content/ct_129977.pdf
  Abstract
  
  This paper summarizes the methods that are typically used in industry to evaluate the service life of low-voltage power circuit breakers and molded case circuit breakers.
  
  It reviews the electrical ratings and endurance requirements set forth in manufacturing standards, the ways that these endurance requirements can be used to develop expectations of circuit breaker life, the methods of maintenance inspections and the interpretations of these inspections.
• Steel, J. G. "Statistical model for single-unit and multiunit circuit breakers." In Proceedings of the Institution of Electrical Engineers, vol. 119, no. 4, pp. 488-492. IET Digital Library, 1972.
• Steel, J. G., and D. T. Swift-Hook. "Statistics of circuit-breaker performance." Electrical Engineers, Proceedings of the Institution of 117, no. 7 (1970): 1337-1345.
  Abstract:
  
  A wide range of data is presented which shows that the electrical performance of high-voltage a.c. circuit breakers is statistical.
  
  The electrical performance cannot be characterized by a single stress level such as a rated stress; a stress ratio is also required to specify the spread of operating conditions over which both clearances and failures occur fairly often. Present test specifications are inadequate to ensure that a circuit breaker is reliable on the basis of the formal tests alone.
  
  Calculations are presented relating the failure rate of a multiunit circuit breaker to that of its separate units. Suggestions are made for improved test strategies in which the present three shots on a multiunit circuit breaker could be supplemented by unit tests to predict a safe rating for the complete circuit breaker.
• UBI FPE CIRCUIT BREAKER TEST RESULTS [Web article] independent test results on UBI circuit breakers used to replace FPE Stab-Lok® circuit breakers find high failure rates.
  
  Also see
  UBI FPE CIRCUIT BREAKER VENDOR COMMENTS [Web article] OPINIONS & discussion of the safety of replacement circuit breakers sold for use in FPE Stab-Lok electrical panels
• UL 67, UL Standard for Safety for Panelboards, Underwriters Laboratories Inc., Northbrook IL 60062: UL
• UL 489, "Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit Breaker Enclosures", Regulatory Services Department UL 333 Pfingsten Road Northbrook, IL 60062 [email protected] 800-595-9844, retrieved 3 April 2015, original source: http://ulstandardsinfonet.ul.com/scopes/scopes.asp?fn=0489.html
  Excerpt:
  
  The requirements of this standard cover molded-case circuit breakers, circuit breaker and ground-fault circuit-interrupters, fused circuit breakers, high-fault protectors, and high-fault modules.
  
  These circuit breakers are specifically intended to provide service entrance, feeder, and branch circuit protection in accordance with the National Installation Codes in Annex B, Ref. No.1. This standard also covers instantaneous-trip circuit breakers (circuit interrupters) specifically intended for use as part of a combination motor controller in accordance with the National Installation Codes in Annex B, Ref. No. 1.
• UL, "Molded Case Circuit Breakers", (2012) Regulatory Services Department UL 333 Pfingsten Road Northbrook, IL 60062 [email protected] 800-595-9844, retrieved 3 April 2015, original source: https://www.ul.com/global/documents/offerings/perspectives/regulators/
  electrical/newsletters/MoldedCaseCircuitBreakersMG.pdf
  Preface:
  
  UL has developed the Molded-Case Circuit Breaker (MCCB) Marking Guide for electrical inspectors, electric utilities, contractors, installers, users, designers, and other interested parties to aid in understanding MCCBs and the applicable codes and standards in order to facilitate a reasonably safe and code-compliant installation of MCCBs.
  
  These circuit breakers are intended to be installed in accordance with the National Electrical Code® (NEC ®) and their listing. These markings are required by UL 489, and are part of the listing.
• Wiermann, T.E., Rasmuson, D.M., Stockton, N.B., "Common-Cause Failure Event Insights: Circuit Breakers", Idaho National Engineering & Environmental Laboratory, U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research, Washington DC 20555, NUREG.CR-6819, Vol., 4, INEEL/EXT-99-00613, retrieved 3 April 2015, original source: http://pbadupws.nrc.gov/docs/ML0317/ML031710861.pdf
  Abstract:
  
  This report documents a study performed on the set of common-cause failures (CCF) of circuit breakes from 1980 to 2000. The data studied here were derived from the NRC CCF database, which is based on US commercial nuclear power plant event data.
  
  This report is the result of an in-depth review of the circuit breaker CCF data and presents several insights ab out the circuit breaker CCF data.
  
  The objective of this document is to look beyond the CCF parameter estimates that can be obtained from the CCF data, to gain further understanding of why CCF events occur and what measures may be taken to prevent, or at least mitigate the effect of, circuit breaker CCF events. This report presents quantitative presentation of the circuit breaker CCF data and discussion of some engineering aspects of the circuit breaker events. [copy on file]
  
  [This report lists 119 individual circuit breaker failures including failure to open or failure to close and attempts to explain the causes involved. e.g. item 49 among failure data:
  
  "One 4160 Vac circuit breaker failed to open and several more were degraded due to hardened grease and lack of lubrication. This problem could affect the ability of the subject breakers to open or close. Maintenance of the breakes was incomplete despite similar failures due to the same cause four years earlier."
• Yacout, A. M., R. N. Hill, L. Van Den Durpel, P. J. Finck, E. A. Schneider, C. G. Bathke, and J. S. Herring. "Dynamic analysis of the AFCI scenarios." Growth 400000 (2004): 500000.
• ZINSCO SYLVANIA ELECTRICAL PANELS [Web article] electrical, fire, and shock hazards associated with Zinsco electrical components, circuit breakers, electrical panels, including certain Sylvania electrical panels and breakers which are in fact of the same product design and origin.
• ZINSCO CIRCUIT BREAKER TEST REPORT [Web article] limited testing of Zinsco® circuit breakers by an independent expert reports a high failure rate for Zinsco circuit breakers

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.

Contributing Authors

• Dr. Jess Aronstein, [email protected] is a research consultant and an electrical engineer in Schenectady, NY. Dr. Aronstein provides forensic engineering services and independent laboratory testing for various agencies. Dr. Aronstein has published widely on and has designed and conducted tests on aluminum wiring failures, Federal Pacific Stab-Lok electrical equipment, and numerous electrical products and hazards.
  
  See ALUMINUM WIRING BIBLIOGRAPHY
  
  and FPE HAZARD ARTICLES, STUDIES,
  
  and BACK-WIRED ELECTRICAL DEVICES
  
  also CIRCUIT BREAKER FAILURE RATES - you are on thi s page
  
  and UBI FPE CIRCUIT BREAKER TEST RESULTS
  
  also ZINSCO FAILURE REPORTS for examples.
• David W. Carrier, electrical engineer, Poughkeepsie, NY 12603 845-430-7527 [email protected]. Mr. Carrier has conducted failures testing on electrical circuit breakers and panel assemblies, supplementing Dr. Jes Aronstein's research into FPE and other circuit breaker performance of other brands such as GE, ITE, Murray, Siemens, Bulldog Pushmatic, Zinsco.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-08-14 by Bryce Nesbitt (mod) - a closer look at the Aronstein/Carrier circuit breaker failure rate studies

Re-posted by Moderator:

NEMA responded to the Jesse Aronstein "holes in the safety net" article, as summarized here: www.ecmag.com/magazine/articles/article-detail/your-business-nema-responds-circuit-breakers-study-suggested-holes-safety-net

"“These experts have reviewed the article … and determined that it creates a misleading impression about the reliability of thermal magnetic circuit breakers in providing general protection against electrical fire hazards,” the memo states."

Any way to get and post the full letter?

Moderator Reply - where to see the full NEMA letter responding to circuit breaker study

@Bryce Nesbitt,

We have contacted NEMA and have requested a copy of the original NEMA letter cited by Mr. Johnson.

A copy is here: NEMA Responds to Circuit Breakers Study That Suggested ‘Holes in Safety Net [PDF] By Timothy Johnson | Sep 10, 2018, Electrical Contractor Magazine, original source: ecmag [dot] com/magazine/articles/article-detail/your-business-nema-responds-circuit-breakers-study-suggested-holes-safety-net

Timothy Johnson is the former digital editor for ELECTRICAL CONTRACTOR magazine.

You should understand that electrical contractors and NEMA, while people whom we deeply respect, are not neutral professionals, and the "experts" mention remain unnamed.

In our opinion, if an expert isn't willing to put their name on their work it's a bit less compelling.

NEMA, the National Electrical Manufacturers Association, is both a standards-setting agency whose committees write standards for the manufacturing of electrical equipment and medical imaging equipment AND a manufacturer's trade association - that is, charged with protecting the interests of its 450 member companies.

Nema's website, informs us:

Founded in 1926, NEMA is an ANSI-accredited Standards Developing Organization made up of business leaders, electrical experts, engineers, scientists, and technicians. NEMA convenes a neutral forum for Members to discuss industry-wide concerns and objectives under a legal umbrella by trained NEMA Staff. - retrieved 2023/08/14 nema [dot] org/about

Circuit Breaker design and testing do not appear in the list of NEMA standards and publications.

But an example of a relevant circuit breaker standard comes from another private, standards producing organization (in the U.S. standards and codes are generally produced by private, not-for-profit companies and organizations rather than by government agencies) - UL - Underwriters Laboratories

I recommend that readers actually look at the Aronstein/Carrier circuit breaker failure rate studies that the engineers cited above have published in IEEE as their data is quite compelling.

Those engineers have no conflicts of interest, report without bias, and found dramatic differences among circuit breaker reliability among a range of U.S. manufacturers. Some breakers performed as expected: extremely well with very few or no failures to trip, while a few other breaker brands and/or models failed at an astonishing rate, as much as 60% of the time in some cases.

It's also my opinion but only an opinion that IEEE is a more independent professional association then a national association of manufacturers of electrical equipment or NEMA.

On 2023-08-16 by InspectApedia Publisher - still some manufacturers that are marketing equipment that does not meet the standard testing requirements

Continuing:

This recent reference is of interest:

Daniel R. Doan, "IAS Open Journal Paper on Fire Safety Problems of Circuit Breakers [Electrical Safety]", IEEE Industry Applications Magazine, vol.29, no.5, pp.7-80, 2023. (access PDF copy at ieeexplore.ieee.org/document/10207915 ).

Readers can read Mr. Doan's paper at the link above or can download this IEEE copy directly

Doan, Daniel R., IAS OPEN JOURNAL PAPER ON FIRE SAFETY PROBLEMS OF CIRCUIT BREAKERS [PDF] in IEEE Industry Applications Magazine, vol. 29, no. 5, pp. 7-80, Sept.-Oct. 2023, doi: 10.1109/MIAS.2023.3283111.

Abstract:
A recent technical paper in IEEE Open Journal of Industry Applications caught my attention. “Faulty Residential Circuit Breakers—A Persistent Fire Safety Problem,” by J. Aronstein [1] , is a very thorough study of fire hazards of residential-type circuit breakers. These circuit breakers are often used in office, shop, and other general buildings in our industrial facilities, so it is a topic of interest.

The author has previously presented and published papers building up to this topic, including “Molded Case Circuit Breakers—Some Holes in the Electrical Safety Net” [2] and “Temperature Sensitivity of Residential Molded Case Circuit Breakers” [3] in IEEE Access in 2018 and 2019, respectively, and “Estimating Fire Losses Associated With Circuit Breaker Malfunction” [4] at the 2011 IEEE Industry Applications Society (IAS) Electrical Safety Workshop.

This newest paper is worth reading; the author shows some excellent graphics of the response of a range of tested circuit breakers and makes a clear case that some manufacturers are using shortcuts to test their products.

Excerpts from Mr. Doan's comments:

It is interesting to note that there is no easy way for users to test their installed circuit breakers; users must rely on the manufacturer to do a thorough test of each breaker.

They must hope the breaker will work properly for many years to come, based on that initial test.

However, the author makes a good point that if manufacturers are using shortcuts to save time during the testing process, then the user is the one who could suffer from potentially faulty equipment in the future.

One example of a shortcut is that breakers are required to open at 135% of rated current after a prescribed period. Quoting from the paper,

“The experimental results provided in this article … clearly show that calibration testing at 200% or 300% of rated current cannot be successfully employed to assure that a breaker will trip as required at or below 135% of its rating.”

The implication is that some manufacturers may be testing at 200% or higher to have a quicker test for each breaker instead of the longer time required to test at 135%.

...

Many manufacturers are making excellent equipment that meets all the requirements, but, as the author shows, there are still some manufacturers that are marketing equipment that does not meet the standard testing requirements.

All industrial, commercial, and residential users of this equipment should learn about this issue to ensure the use of quality equipment.

Thank you to Mr. Aronstein, for these efforts to bring this issue to the forefront and for a commitment to electrical safety.

the following is an excerpt from personal communication on this question, Aronstein to Friedman, 2023/08/16

Dr. Aronstein comments:

The underlying problem is the long-standing misconception that testing at high current (200% or 300% of rated) can reliably indicate whether a breaker will trip properly at 135%. Not true for all breaker designs!

Here's a statement from a Schneider field testing manual:

"Test each pole of the circuit breaker individually at 300% of rated current using a high-current, low-voltage ac power supply.

Record and compare the trip test values to those in Inverse-Time Overcurrent Trip Test. As long as the recorded trip times are below the maximum trip times, the circuit breaker is providing acceptable thermal protection."

...
Regarding the portion of that statement

"As long as the recorded trip times are below the maximum trip times, the circuit breaker is providing acceptable thermal protection."

That's the misconception. (Similar for new breaker testing at the factory.)

[Paraphrasing from Aronstein's note to Friedman] ... this misconception and situation have existed for more than 60 years!

On 2022-11-04 by InspectApedia (Editor) - testing of Siemens panels & breakers

Follow-up comment from email exchange with Dr. Jess Aronstein - excerpting from private email 2022/10/31

Reader Comment: do you want my old FPE breakers for testing?

In large part to your published research I’m in the process of having the Federal Pioneer panel in my house replaced. Thank you for your efforts in bringing the danger associated with these panels to the public’s attention.

I’m located in Ottawa, Canada and our home was built in 2004.

I’m writing to you to find out if you have any interest in conducting any tests on the old panel once it has been removed to increase your sample size?

I’m also interested in your opinion on Siemens panels & breakers as that is what the electrician is proposing as they are made in Canada. I know that you aren’t a fan of the US Siemens breakers but it wasn’t clear to me if your testing had included Canadian Siemens panels.

Dr. Aronstein's reply - [Excerpt]

... discussing circuit breaker replacement for a Siemens electrical panel located in Canada ...

Siemens breakers have not fared well when tested for their basic function.

Previous tests of new Siemens breakers in 2017 showed a 50% failure to trip as required at or below 135% of rated current.

Samples purchased and tested in 2021 had a 28% failure rate. These Siemens breakers have both CSA and UL logos, for distribution both north and south of the border. The labeling indicates that they were assembled in Mexico.

(Recently manufactured Siemens arc-fault and ground-fault type breakers that I have seen are assembled in the Phillipines, but I have no test data on them.)

I would be surprised if the Siemens breakers that your electrician is proposing to install are made or assembled in Canada.

If possible, take a look at some samples to determine country of origin of the breakers.

The panel itself may be manufactured or assembled in Canada. I have no info on that.

Whatever [replacement electrical panel] brand you ultimately choose, insist on copper bus-bar. The clip-on contacts where the breaker connects to the bus-bar are failure-prone with aluminum bus-bar.

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[Note: if /when additional Siemens circuit breaker testing is completed we'll report those results here - Ed.]

On 2022-06-25 by Anonymous - hair dryer causes circuit breaker to trip off

I was vacuuming n my daughter was in the bathroom straightening her hair the breaker kept flipping off.

i turned everything off fans n air-conditioners eventually all the power stayed off in our bathroom and bedroom n part of our laundry room changed the outlet in the bathroom since it's the ones with the buttons and seems to control other power in other rooms didn't help tested the breaker by switching to another part of the house (dishwasher) it still powered it on any idea what it could be

On 2022-08-13 by InspectApedia-911 (mod) - possibly the circuit was overloaded

@Anonymous,

If the bathroom electrical circuit where the hair dryer was connected and running and the circuit into which you plugged and ran your vacuum cleaner, it's entirely possible that the circuit was simply over-loaded - in which case the breaker is operating as it should, protecting your building from a fire.

If the circuit tripped off because a GFCI device sensed a fault (such as a current leak or water), then a GFCI-protection device somewhere on that circuit (in the panel or at a wall receptacle) has tripped OFF.

In that case you need to find the GFCI receptacle that is electrically "upstream" from the bath or vacuum-cleaner receptacle and press its RESET button. (Or there may be a GFCI circuit breaker in the panel - also sporting a RESET button).

You may have to wait 30 seconds or so before the RESET button will work.

On 2021-09-30 by Ernie - What line of Square-D circuit breaker were tested?

What line of Square-D circuit breaker were tested? Specifically, were Homeline breakers included? I’m in the process of working with my electrician to specify a panel replacement for an old Zinsco panel. I’m trying to understand the diff differences between the Square-D Homeline and the significantly more expensive QO series.

On 2021-10-01 by inspectapedia.com.moderator - were Homeline breakers included in the Square-D circuit breaker testing?

@Ernie,

Actually I don't remember however those details are in the test reports which you can download as a PDF, it's referenced in this page and in this article series.

On 2021-04-07 by amarchdesign1 - worried that electrician used aluminum wiring in my house - lights are flickering

I just moved to a house that was renovated recently. My electrician wired the whole house with permit from the City and passed the inspection. However, he did not mention that he used the aluminum wiring. I believe this was done because it was less expensive to do the job. My house is constantly flickering, the lights especially when the AC goes on.

I sent a picture of my electrical panel to a friend of mine who happens to be an electrical engineer and he stated that the wiring appears to be aluminum and can cause a fire.

I am afraid to live in this house and I need to know what can be done?

On 2021-04-07 by danjoefriedman (mod) - flickering lights may indicate dangerous situation but not solid conductor aluminum branch circuit wiring

@amarchdesign1,

There is no reasonable chance that your electrician wired your whole house with solid conductor aluminum branch circuit wiring (lights, receptacles, etc.) - that wire is not sold in North America for house-wiring.

The electrician might have used multi-strand aluminum electrical wire for a few high-amp circuits such as an electric clothes dryer or range. That's permitted provided the connections were made properly using an antioxidant paste, abrasion, and proper connectors approved for use with aluminum wire.

So if your lights are flickering there should be another cause. Still, that situation can be dangerous - you need an on-site licensed electrician.

See FLICKERING LIGHT DIAGNOSIS

Also, to rule out the chance that someone claimed to have re-wired a home that previously had aluminum wiring, and that the re-wiring was incomplete or improper, be sure to read

ALUMINUM WIRING HAZARDS & REPAIRS - overheating or corroded connections can cause flickering lights

In that article you'll see links to articles on how to identify aluminum electrical wire and on what repairs are safe and proper.

Reader comment: field report: burned contact inside QO Circuit Breaker

It was a good QO breaker. It wasn't warped or cooked or anything, just a bit blackened at the contact points inside. After testing today by letting the water heater heat from tap cold, the new breaker doesn't seem meaningfully cooler, which makes me feel like it wasn't too bad.

I *did* crack the tip of a flat head bit when torquing the new breaker lug down to 45 inch pounds or so. The square drive tend to round out, and the fancy quadrex bits I got on McMaster-Carr proved useless. I'll be trying "ecx* bits next, but seriously, when will manufacturers get serious and just use torx drive screws?…

Really though, when will manufacturers, or UL for that matter, start using torx screw drives for these things? It would be a million times better. And might be a good way to subconsciously convince people to use torque screwdrivers. - Alexander G. Riccio by private email 29 June 2023

Other comments by Mr. Riccio are at

• RECEPTACLE WIRE-TO-CONNECTOR CONTACT AREA SIZES  - Binding Head Screw Torque Concerns on electrical components - Apr 13, 2023 
• GFCI DEVICE SELECTION & WIRING  - GFCI model that provides a Trip Alarm
• ELECTRICAL RECEPTACLE WIRING SERIES vs PARALLEL - Pigtailing vs daisy-chaining electrical receptacles
• BATHROOM MOLD REMOVAL / PREVENTION  - bathroom mold cleanup & use of sealants

Moderator reply:

Thank you for those at a details. Yes there's a long history of manufacturers struggling with cost and profit trade-offs and sometimes it's safety that suffers. Are you interested in writing up or providing raw text and images to describe your circuit breaker investigation and results? That's be interesting information that our ee type readers would appreciate.

Reader follow-up:

I really should write it all up once I get to the bottom of things! ... I don't know when, but you're free to use anything I provided in the meantime!

On 2019-09-01 by Alan - does not agree with circuit breaker research

The above article on residential grade circuit breakers is a bit misleading. All breakers have a trip curve published by the mfg. Reading the curve is a bit daunting until you learn what they are telling you.

A trip requires current thru time to cause an action. A 25 amp load on a 20 amp breaker would take MINUTES to trip. More current less time. When we tested a large breaker we used 3x, 6x and 10x for current settings. (large breaker = over 100 amp frame). Only grossly overloaded/faulted circuits cause an immediate trip.

Or in other words Long Time, Short Time, and Instantaneous, only one of these values is available on a residential breaker, Long Time. Residential breakers are sold at a loss because that is how the industry goes to market. They make it up on the larger breakers for uses other than residential.
I

do not like the term "short circuit" as faults follow ALL PATHS not just the shortest one.

Image chosen is not mine it was found with a google search http://www.nuclearelectricalengineer.com/three-fault-regions-time-current-plot/ all credit goes to the original poster.

On 2019-09-01 - by (mod) - reading the circuit breaker trip curve

Thank you Alan. I agree that there is more to say on this. The two Engineers whose work is described and reported in these articles are of course experts in the field as well. The testing that we report generally is following the specifications of UL 486 and similar standards in order for the findings to be able to be compared with other products and tests. I agree that your additional tests are quite interesting in the results are important. If there's published work from your area that we could include here would be glad to do so.

Just as a point of clarity, the significance of the article on this page and the supporting test results is that a significant percentage of circuit breakers from some manufacturers have an extremely high failure rate.

That will come as a surprise to many consumers and others who assume that if a circuit breaker is available in the electrical supply market it is reliable.

In my opinion as well as those in nationally-recognized independent experts, those failing circuit breakers are unsafe.

It seems likely that the underlying problem is that there's no independent agency serving as the electrical testing police.

Companies do their own testing and certify their products as meeting standards.

In some cases those tests have proven credible and in others as shown here there's a significant question raised.

On 2019-04-27 by Dawn - our house lights are flickering when its windy

Our lights flickered a couple times and then we loss power to two sections of our house. There is a lot of wind tonight.

On 2019-04-27 1 by (mod) - flickering lights in high wind

Wind could disturb a loose or poor service entry wire connection causing partial loss of power - e.g. on one side of the panel or half of your electrical circuits.

Watch out: if you see disturbed overhead service entry wires (between the utility power lines in the street and your house) OR in the street itself that is a VERY DANGEROUS condition risking death by electrocution of someone touches those downed electrical wires or even if they go near them or touch something the wires touch.

In that case stay away and call your electric utility and emergency services for help.

On 2017-11-19 by Ray Kopylciw - could a bad breaker be causing our microwave to shut down

We have a oven microwave combo unit with intermittent power shut down and right after power comes back showing on LED board that needs to be time and date reset. Occasional heat in oven not getting to what it registers by 50 or so degrees. Could the breaker be causing these short fails.

On 2017-11-19 by (mod)

Yes the problem could be a bad circuit breaker but I'd be looking first for a loose electrical connection, starting at the electrical recptacle where the microwave is connected.

...

Continue reading  at CIRCUIT BREAKER RELIABILITY TESTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AFCIs ARC FAULT CIRCUIT INTERRUPTERS
• CIRCUIT BREAKER FAILURE RATES
  • BACK-WIRED ELECTRICAL DEVICES
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  • FEDERAL PIONEER PANEL SAFETY
  • FPE FAILURE FIELD REPORTS
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  • MURRAY CIRCUIT BREAKER HAZARDS
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  • SIEMENS MURRAY Recall
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  • SQUARE-D AFCI RECALL 2004
  • SQUARE-D COUNTERFEIT BREAKER RECALL
  • TEST MAIN BREAKERS & FUSES
  • UBI FPE CIRCUIT BREAKER TEST RESULTS
  • ZINSCO CIRCUIT BREAKER INDEPENDENT TESTS
  • ZINSCO CIRCUIT BREAKER TEST REPORT
• CIRCUIT BREAKER / FUSE INSPECTION
• CIRCUIT BREAKER MAIN or FUSE TEST
• CIRCUIT BREAKER REPLACEMENT
• CIRCUIT BREAKER RESET STEPS
• CIRCUIT BREAKERS RE-CONDITIONED USED
• CIRCUIT BREAKER RELIABILITY TESTS
• GFCI TEST PROCEDURES
• MOBILE HOME ELECTRICAL GFCI DIAGNOSIS

Suggested citation for this web page

CIRCUIT BREAKER FAILURE RATES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to ELECTRICAL INSPECTION & TESTING

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