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What do SWD and HID ratings signify? What is the difference between them?

Circuit breakers used to switch 120V or 277V fluorescent lighting circuits must be listed and marked ``SWD`` or ``HID.`` Circuit breakers used to switch high-intensity discharge lighting circuits must be listed and marked ``HID.`` UL 489 (Standard on Molded Case Circuit Breakers) permits ``HID`` breakers to be rated up to 50A, whereas an ``SWD`` breaker is rated up to 20A. The tests for ``HID`` breakers include an endurance test at 75 percent power factor, whereas ``SWD`` breakers are endurance-tested at 100 percent power factor. The contacts and the spring of an ``HID`` breaker are heavier duty, to dissipate the increased heat from greater current flow during the HID ignition period. [Courtesy of Mike Holt newsletter 10/22/03]


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