Zinsco Circuit Breaker Failure Test Report

This article provides the result of testing to-date of Zinsco brand circuit breakers and results of a very small sampling of UBI-brand replacement circuit breakers for Zinsco type electrical panels. Testing of 111 Zinsco-Type circuit breakers to date has found high failure rates.

Page top photograph: arcing burns on the buss connector clips in a single-pole 50-A Zinsco circuit breaker, courtesy of Jess Aronstein.

This article series describes the identification, hazards, reliability & field failure reports of Zinsco or Sylvania-Zinsco or Kearney electrical panels: overheating, failure to trip, fires, other defects.

Zinsco® Circuit Breaker Test & Failure Results

Zinsco Circuit Breaker Failure Test Results To Date

Dr. Jess Aronstein, an independent forensic testing engineer has tested samples of Zinsco and UBI-Zinsco circuit breakers retrieved from in-use electrical panels from several locations in the United States. As of 2017 the Zinsco type circuit breaker test number was 111 breakers and included four of UBI Zinsco breakers.

Test results applying the UL-489 requirement for the breaker to trip at 135% of rated current found 32 failures out of 111 Zinsco breakers, including two that jammed (no trip at >200% of current rating). That's a 28.8% failure rate for the test group.

We (Friedman & Aronstein) think that across the electrical industry for residential circuit breakers, the typical failure-to-trip rate for these devices is less than 1%.

[Click to enlarge any image]

Dr. Aronstein has also tested 4 UBI Zinsco type replacement breakers. All 4 of the UBI Zinsco replacement circuit breakers failed the UL 489 requirement to trip at 135% of rated current, a 100% failure rate - including one jam.

The circuit breakers included units rated at 15A, 20A, 30A, 40A, and 50A, and further included both single pole and double-pole breakers.

Illustrated here: a screen shot of Aronstein's test results showing the applied test load in current (Amps) on the vertical axis and elapsed time until the breaker trips on the horizontal axis.

For the breaker illustrated here, #r 15-5 in the table below, after two hours of total test time including one hour at 135% of rated current, the Zinsco circuit breaker had not tripped.

Notes to the table above

Data as of 20 March 2017, by private email, J. Aronstein to D. Friedman et als.

 

Example Zinsco Breaker Test Results

The table below shows the test results for an example subset of 14 Zinsco-brand circuit breakers submitted to Jess Aronstein by Thomas D'Agostino (cited below).

These breakers are a proper subset of the 98 Zinsco-brand circuit breakers tested to date. Overall test results and failure percentage for 98 Zinsco and 3 UBI-Zinsco-replacement breakers tested to date were give just above.

Notes to the table above

Data in the table above provides details of individucal Zinsco type breaker tests and represents earlire data: In this table data is of 18 December 2016 when Dr. Aronstein had tested 98 Zinsco brand circuit breakers from different sources.

1. The table illustrates example rest results for a subset of 21 circuit breakers all from the same building complex.

2. See the circuit breaker test criteria and test consultant citations provided in the article below.

Watch out: while a visual inspection of circuit breakers might spot evidence of corrosion, overheating, or physical damage rendering those breakers unsafe and unreliable, the more-complete and UL-standard-compliant circuit breaker testing conducted by Dr. Aronstein requires a specialized electrical test lab. This is beyond the scope of a licensed electrician.

Visually inspecting or toggling the breakers will not detect this type of fault.

DO NOT attempt to test circuit breakers in-place by overloading them. That approach risks fire or injury.

 

Zinsco Circuit Breaker Failure Test Criteria

For purposes of these tests, "Failure" means that the circuit breaker failed to trip within one hour of submitting the circuit breaker to an overload of 135% of rated current. These failures occurred on (nn) single pole breakers and on at least one pole of (nn) two-pole circuit breakers.

The test current applied for this study is defined by the applicable UL standard, and the failure criterion being used is that of the UL standard that requires these breaker to trip within 1 hour at 135% of rated current.

Throughout this article series about Zinsco-brand circuit breaker reliability and safety we have asked readers to contribute for independent testing used, replacement, or new Zinsco-brand or UBI-brand replacement circuit breakers intended for use in Zinsco-brand electrical panels.

Previously at ZINSCO FAILURE REPORTS we reported visual observation of significant Zinsco breaker damage in about 25% of the Zinsco/Sylvania panels that were checked.

Zinsco Circuit Breaker Tests

Zinsco Breaker Failiure Test Information Sources

• ZINSCO CIRCUIT BREAKER TEST REPORT
• ZINSCO SYLVANIA KEARNEY FAILURE REPORTS
• CIRCUIT BREAKER FAILURE RATES
• Dr. Jess Aronstein, protune@aol.com 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 and also ZINSCO FAILURE REPORTS for examples.
• Thomas J. D'Agostino, Ronkonkoma, New York 11779. Tel: 631-467-4663, Cell: 631-831-2076, Email tdagosti@aol.com. Mr. D'Agostino is a licensed professional engineer, a professional home inspector, an ASHI member, and is a contributor to InspectApedia.com, e.g. at COPPER-CLAD ALUMINUM WIRE. Mr. Tom D'Agostino was employed at Underwriters Laboratories from 1969 to 1996 and spent a decade and a half studying and testing the safety of aluminum electrical wiring.
• UL 489 Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures. UL Standards, retrieved 2016/12/19, original source: https://standardscatalog.ul.com/standards/en/standard_489 UL has offices world wide and has its headquarters in the U.S. in Northbrook, IL.
  Excerpts:
  1 Scope
  
  1.1 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. 1.2 This standard covers molded-case switches and fused molded-case switches.
  
  UL certifies, validates, tests, verifies, inspects, audits, advises and educates. We provide the knowledge and expertise to help customers navigate growing complexities across the supply chain from compliance and regulatory issues to trade challenges and market access.
• RUST & CORROSION in ELECTRICAL PANELS, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels. Because exposure to water or high moisture levels may affect the performacne of any circuit breaker, readers may also want to see this article.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website. We do not sell products nor services.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles.

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Continue reading  at ZINSCO SYLVANIA KEARNEY FAILURE REPORTS - field failure reports of Zinsco type circuit breakers, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see

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• CIRCUIT BREAKER FAILURE RATES - discussion of electrical safety standards, product testing, test supervision, test results publication
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Citations & References

In addition to any citations in the article above, a full list is available on request.

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