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Arcing on a 50A single  pole breaker tested by Aronstein (C) InspectApedia.com & Jess Aronstein Zinsco® Circuit Breaker Failure Test Report
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  • ZINSCO CIRCUIT BREAKER TEST REPORT - CONTENTS: limited testing of Zinsco® circuit breakers & UBI-Zinsco circuit breakers by an independent expert reports a high failure rate for Zinsco circuit breakers
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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.



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Zinsco® Circuit Breaker Test & Failure Results

Screen shot of Zinsco circuit breaker no-trip failure test by Aronstein 2016 (C) InspectApedia.com & Dr. Jess Aronstein

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.

Table I Summary of Zinsco & UBI-Brand Zinsco Replacement Circuit Breaker Failure Test Results

Summary: tests to 20 March 2017

  Number Tested n=1111 Failure Percent
Total # Zinsco-Type Circuit Breakers Tested ( Zinsco + UBI-ZInsco) 111  
   Breakers Failing to Meet UL 135% Trip Requirement 32 28.8%
   Critical Safety Failures (no trip @ 200%) Subset of the 135% no-trip total 2* 1.8%
         * Subset of the 135% no-trip total
 
Zinsco Brand Circuit Breaker Tests Number Tested Failure Percent
Total # Zinsco Brand Circuit Breakers Tested 1071  
   Breakers Failing to Meet UL 135% Trip Requirement 28 26.2%
   Critical Safety Failures (no trip @ 200%)
      * Subset of the 135% no-trip total
1* 0.9 %
     
UBI - Zinsco Circuit Breaker Tests    
Total # Double Pole UBI Breakers Tested 41  
   Breakers Failing to Meet UL 135% Trip Requirement 4 100.0%
   Critical Safety Failures (no trip @ 200%)
      * Subset of the 135% no-trip total
1* 25.0%

Notes:

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.

Table II Example Zinsco Circuit Breaker Failure Test Results1

Breaker ID & Ampacity Breaker Type:
Poles
Test Result Comments
15-1 Single pole Failed - No trip >1 Hr @135% of rated current  
15-2 Single pole OK, tripped at 02:51 (mm:ss) @135% of rated current  
15-3 Single pole OK, tripped at 10:19 @135% of rated current  
15-4 Double - Pole A Failed - No trip >1 Hr @135% of rated current In proper two-pole circuit breaker operation, if one pole trips the breaker should force both poles to trip to the "OFF" Position - Ed.
Double - Pole B OK, tripped at 05:49 @135% of rated current
15-5 Double - Pole A Failed - No trip >1 Hr @135% of rated current This was the worst-case failure of the lot - see screen shot above.
Double - Pole B Failed - No trip >1 Hr @135% of rated current
20-1 Single pole OK, tripped at 10:12 @135% of rated current  
20-2 Single pole Failed - No trip >1 Hr @135% of rated current  
20-3 Double - Pole A Failed - No trip >1 Hr @135% of rated current  
Double - Pole B Failed - No trip >1 Hr @135% of rated current  
20-4 Double - Pole A OK, tripped at 13:04 @135% of rated current  
Double - Pole B Failed - No trip >1 Hr @135% of rated current  
30-1 Double - Pole A OK, tripped at 02:21 @135% of rated current  
Double - Pole B OK, tripped at 01:28 @135% of rated current  
40-1 Double - Pole A OK, tripped at 16:46 @135% of rated current  
Double - Pole B OK, tripped at 08:20 @135% of rated current  
40-2 Double - Pole A Failed - No trip >1 Hr @135% of rated current  
Double - Pole B Failed - No trip >1 Hr @135% of rated current  
50-1 Single pole OK, tripped at 4:20 @135% of rated current Had been arcing at the busbar contact - see photo at the top of this page
50-2 Single pole OK, tripped at 8:51 @135% of rated current  
       

Notes:

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 Breakers Wanted for Testing

Readers who are replacing a Zinsco, Zinsco-Sylvania, or Kearney-Zinsco type electrical panel and who are willing to contribute their old circuit breakers for independent testing are invited to CONTACT us by email or contact Dr. Jess Aronstein directly by email to: protune@aol.com

Test Information Sources:

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 closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CIRCUIT BREAKER FAILURE RATES - discussion of electrical safety standards, product testing, test supervision, test results publication

Or see UBI FPE CIRCUIT BREAKER TEST RESULTS for similar testing procedures & results on replacement circuit breakers for FPE Stab-Lok panels

Zinsco Electrical Panel & Circuit Breaker Articles

 

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