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CALIBRATION AND CONDITION TESTS OF MOLDED CASE CIRCUIT BREAKERS - Federal Pacific Stab Lok Breakers - CPSC Data
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FAILURE CONDITION |
FAILURES |
|
|
% (#failed/#tested) |
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|
Before Mechanical Operations |
After Mechanical Operations |
|
|
No-trip: 200% of rating, both poles |
0% (0/122) |
1% (1/107) |
|
No-trip: 200% of rating, individual poles |
1% (3/244) |
10% (21/214) |
|
No-trip: 135% of rating, both poles* |
25% (31/122) |
36% (39/107) |
|
No-trip: 135% of rating, individual poles |
51% (125/244) |
65% (144/220) |
|
Trip: 100% of rating, both poles* |
3% (4/122) |
6% (7/111) |
|
Dielectric Breakdown (short)* |
0 |
1% (1/111) |
|
TABLE 1 - SUMMARY OF FAILURES *UL 489 Test Conditions | ||
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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