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FPE Sab-Lok circuit breaker failure rate data: this article presents research data demonstrating the failure rates of Federal Pacific Electric Stab-Lok® circuit breakers.
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CPSC-C-81-1429 December 30, 1982
Calibration tests have been performed on 122 two-pole Federal Pacific Electric circuit breakers. The calibration tests were performed -in accordance with UL Standard 489 except for or a difference in the sequence of calibrations. UL 489 is the applicable standard that the breakers are presumed to meet. In most cases, the calibration tests were repeated after 500 off-on mechanical operations of the toggle handle..
The circuit breakers tested were supplied by CPSC and came from several sources. Most were provided to CPSC by Federal Pacific Electric, some were purchased new by CPSC staff members at retail outlets, and a few were removed from existing installations. The breaker ratings tested were 30 A (30 two-pole breakers tested), 40A (35), 50A(20), 60A(7) and 80A (30). The tests include performance at 100%, 135%, and 200% of ratings, and dielectric tests.
A substantial number of breakers failed the calibrations testing, both before and after the mechanical toggle operations. Failures were evident with both poles carrying current as well as with one-pole operation. Specifically, the failures are summarized as follows:
The failures appeared. among breakers of all ratings, none were failure-free. Most of the "no-trip' conditions were sustained for four hours well beyond the UL specification. These were not marginal failures with respect to the failure criteria. The data suggests that, on the average, the mechanical operations result in increased failures. This was .'not strictly the case on a sample-to-sample basis.
The failures relate to hazardous conditions in at least two ways. First, a fault in the wiring or utilization equipment which causes excessive- current-can result in fire if the circuit is not opened by the breaker -- this is its principal functional requirement.
Secondly, it was determined in these tests that some of the breakers overheat to hazardous levels when subjected to overcurrent conditions (due to their own failure to trip) for sustained periods of time.
The overheating can result in incapacitation of the breaker (i.e.: it will no longer open under any condition), and the temperature can be high enough to ignite fire in the vicinity of the breaker, as evidenced by charring of the case on some samples.
NOTE: this text is quoted verbatim from pages 3-5 of "Calibration and Condition Tests of Molded Case Circuit Breakers, Final Report: Contract CPSC-C-81-1429 December 30, 1982," obtained from the US Consumer Product Safety Commission as a FOIA request.
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