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.

中文翻译：

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住宅断路器故障——一个持续存在的消防安全问题

住宅分支电路的断路器必须在等于或低于额定电流的 135% 时跳闸。不符合该要求的断路器是有缺陷的。对从零售渠道购买的两个品牌的样品进行基本校准测试。这两个品牌都在 4 年前进行了测试。一个品牌之前的样品有 50% 的缺陷，2021 年生产的新样品有 28% 的缺陷。之前无缺陷的第二个品牌再次无缺陷。过去和现在的测试结果表明，一些制造商正在校准断路器以使其跳闸过于接近允许的电流上限，并通过在更高电流下进行测试来检查校准情况。表明在 200% 额定电流下进行的标准校准测试无法表明断路器是否会按照适用标准的要求在 135% 额定电流下正常跳闸。第三个经过测试的品牌最近上市。它的热磁断路器正确跳闸，但该品牌的液压磁断路器不稳定，38% 的样品出现故障。故障归因于导致触发机构机械结合的热变形。一些缺陷率高的断路器品牌已经在分销链中多年，并永久安装在家庭中。这些住宅的居住者发生火灾和受伤的风险显着增加。讨论了这个问题的长期历史和消防安全后果。故障归因于导致触发机构机械结合的热变形。一些缺陷率高的断路器品牌已经在分销链中多年，并永久安装在家庭中。这些住宅的居住者发生火灾和受伤的风险显着增加。讨论了这个问题的长期历史和消防安全后果。故障归因于导致触发机构机械结合的热变形。一些缺陷率高的断路器品牌已经在分销链中多年，并永久安装在家庭中。这些住宅的居住者发生火灾和受伤的风险显着增加。讨论了这个问题的长期历史和消防安全后果。