Molded Case Circuit Breakers - Some Holes in the Electrical Safety Net

Aronstein, J.; Carrier, David W.

doi:10.1109/access.2018.2803298

Cited by 16 publications

(19 citation statements)

References 2 publications

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“…3. Each circuit breaker brand is identified by the same number used in a previous study [9]. A straight line was determined to be the best fit for the data and it is drawn through the data points for each breaker using computer programmed least squares regression analysis.…”

Section: Test Resultsmentioning

confidence: 99%

“…This demonstrates that at low ambient temperature, a breaker with a high temperature coefficient may fail to prevent a plausible fire ignition risk even if it meets the UL489 calibration requirement. This does not represent the worst case from a fire risk standpoint, however, because not all breakers installed in homes meet the calibration requirement [9]. That specifically applies to Brand 13 breakers, which are reported in [9] to have a high rate of failure to meet the UL489 135% ''must trip'' calibration requirement.…”

Section: A Cold Temperature Operation and Fire Riskmentioning

confidence: 99%

“…If calibrated at higher trip current, the possibility of high temperature nuisance tripping is reduced. The trip points of the Brand 13 breakers tested in [9] is distributed around 135% of rating as an approximate mean value rather than as an upper limit, so that many of those samples failed to meet the UL489 135% calibration requirement. Calibrating high may be a measure taken by that manufacturer to minimize nuisance tripping complaints that might result from the relatively high sensitivity to temperature of their breakers.…”

Section: B Nuisance Trippingmentioning

confidence: 99%

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Temperature Sensitivity of Residential Molded Case Circuit Breakers

Aronstein

2019

IEEE Access

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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 15 A breakers will not trip at 25 A, which would be the current load of two 1500 W 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.INDEX TERMS Breaker, circuit breaker, electrical fire safety, fire investigation, load center, outdoor, residential, temperature, test data, test method, testing.

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Section: Test Resultsmentioning

confidence: 99%

Section: A Cold Temperature Operation and Fire Riskmentioning

confidence: 99%

Section: B Nuisance Trippingmentioning

confidence: 99%

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Temperature Sensitivity of Residential Molded Case Circuit Breakers

Aronstein

2019

IEEE Access

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“…In 2012, when that analysis was published, only Brand X residential breakers were publicly proven to have a high failure rate. The concept that it was an outlier was often challenged, leading to extensive testing of other brands of breakers from homes, referred to as "used" breakers [6]. Those who questioned the concept that Brand X was the only problematic line of breakers were correct.…”

Section: Introductionmentioning

confidence: 99%

Faulty Residential Circuit Breakers—A Persistent Fire Safety Problem

Aronstein

2023

IEEE Open J. Ind. Applicat.

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Circuit breakers for residential branch circuits must trip at or below 135% of rated current. A breaker that fails that requirement is defective. Samples of two brands, purchased from retail sources, are tested for that basic calibration. Both brands were tested 4 years ago. Previous samples of one brand were 50% defective, and new samples manufactured in 2021 are 28% defective. The second brand, previously defect-free, is again defect-free. The test results, past and present, imply that some manufacturers are calibrating breakers to trip too close to the allowable upper current limit, and are checking calibration by testing at higher current. The standard calibration test at 200% of rated current is shown to be incapable of indicating whether or not a breaker will trip properly, as required by the applicable standard, at 135% of rated current. A third brand tested came on the market recently. Its thermal-magnetic breakers trip correctly, but the brand's hydraulic-magnetic breakers are erratic, with 38% of the samples malfunctioning. The malfunctions are attributed to thermal distortion that causes mechanical binding of the triggering mechanism. Some breaker brands with a high defect rate have been in the distribution chain for many years and are permanently installed in homes. The increased risk of fire and injury for the occupants of these dwellings is significant. The long-standing history of this problem and the fire safety consequences are discussed.INDEX TERMS Circuit breaker, electrical fires, electrical safety, failure, fire, quality control, residential, risk, test data, test method, test results, testing.

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“…The intelligent air circuit breaker (ACB) and molded case circuit breaker (MCCB) (used as master protection switch and slave protection switch, respectively) [2][3][4][5][6][7][8][9][10] were commercialized (e.g., ABB Emax 2 series and Tmax T series). Although miniature circuit breakers (MCBs) are required to protect most of the terminal electrical equipment in the power grid [11], the commercialization of an intelligent MCB is constrained by its operating principle.…”

Section: Introductionmentioning

confidence: 99%

An electrothermal current prediction method for overload protection of miniature circuit breakers

Lyu¹,

Zong²

2020

Turk J Elec Eng & Comp Sci

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Traditional miniature circuit breakers (MCBs) cannot meet the requirement for the intelligence of distributing apparatuses in a smart grid. The intellectualization of MCBs is restricted due to the lack of appropriate current measurement methods. Thus, an electrothermal current prediction method is proposed based on the derived relationship between root-mean-square (RMS) current and steady-state temperature rise. A fast acquisition algorithm is used to obtain the required temperature rise before thermal equilibrium to highly reduce the total time consumption. The presented prediction method is found immunized against the ambient temperature. The theory is validated with experiments using a thermostat. The tested steady-state accuracy and transient performance could meet the overload protection requirements without being affected by the environmental temperature.

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Molded Case Circuit Breakers - Some Holes in the Electrical Safety Net

Cited by 16 publications

References 2 publications

Temperature Sensitivity of Residential Molded Case Circuit Breakers

Temperature Sensitivity of Residential Molded Case Circuit Breakers

Faulty Residential Circuit Breakers—A Persistent Fire Safety Problem

An electrothermal current prediction method for overload protection of miniature circuit breakers

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