- Location
- Massachusetts
Does anyone know the design life of a typical circuit breaker is?
How many faults before it is considered done?
How many faults before it is considered done?
Interrupting test
One break operation, followed by a cool down period, followed by a "making and breaking" operation.
(effectively it allows one rest of a breaker that has tripped at full fault current rating)
Thanks, that was what I was looking for.
I have to admit I really don't understand what it is saying.
Is it saying, 'one fault, rest, close, another fault, junk?
The rest and reclose seems to be testing for welded contacts.
Yes,Is it saying, 'one fault, rest, close, another fault, junk?
The following pdf explains:
http://static.schneider-electric.us...nsulated Case Circuit Breakers/0613DB9902.pdf
Yes,
After a full 'AIC' rated fault, the breaker needs to be replaced.
The rest and reclose seems to be testing for welded contacts.
Some companies must repeatedly test at least a sample of breakers at full fault current until the breaker stops functioning, catches fire, explodes, or fails in some obvious way. Otherwise I don't see how they can be assured of the certainty of withstanding just one fault trip.
After a full 'AIC' rated fault, the breaker needs to be replaced.
I have previously stated the NEMA test is Trip - Wait (2 sec to 1 hour)- Reset- Close &Trip.Jim, I read the UL test criteria as two AIC rated faults, how do you get one? Not saying you are wrong, maybe I am understanding it incorrectly.
That makes sense. How about this? 1st AIC trip, order spare. 2nd AIC trip, replaceI have previously stated the NEMA test is Trip - Wait (2 sec to 1 hour)- Reset- Close &Trip.
So yes, while the breaker can experience two full AIC trips, it can only be rest once. Therefore the breaker would not need to be replaced until you wanted to reset it a second time.
What really confuses the issue is how many >600% FLA and less than full AIC trips can a breaker tolerate?
[FONT=Helvetica-Bold+2]Of course, this is strictly personal opinion, but if there is any reason to believe a molded case circuit breaker, has interrupted a fault, it should be replaced. This is especially true for the instantaneous only type commonly used in combination starters.[/FONT]Does anyone know the design life of a typical circuit breaker is?
How many faults before it is considered done?
Interestingly enough, NEMA AB 4-1996 (GUIDELINES FOR INSPECTION AND PREVENTIVE MAINTENANCE OF MOLDED CASE CIRCUIT BREAKERS USED IN COMMERCIAL AND INDUSTRIAL APPLICATIONS) recommended a short circuit test as part of the inspection procedures ? this was the MCCB?s second fault!!! I pointed this out during one of the IEEE/PCIC Tech Committee meetings I was working on. The MCCB reps choked. (Several users did too) Since then, NEMA AB 4 has been rewritten slightly. It is available for free at NEMAs website.[FONT=Helvetica-Bold+2][FONT=Helvetica-Bold+2]3.35 Circuit breaker useful life[/FONT]
[FONT=Times-Roman+2]It is prudent to replace any MCCB that has interrupted, at most, two faults at rated maximum current. This is so because the MCCB short-circuit proof test consists of an ?O-t-CO? sequence, which means that in proof testing of the circuit-breaker design and in periodic follow-up testing thereafter, the circuit breaker is required to open a fault from an initially closed position (corresponding to the ?O? operation), then after a period of time (t) to reset is allowed, to be closed into a maximum fault and trip open for a second time (corresponding to the ?CO? operation). This demonstrates a circuit breaker?s ability to perform at least two maximum level fault interruptions with the second at least a little worse than the first. No maintenance of the circuit breaker on test is permitted between interruptions.[/FONT]
[FONT=Times-Roman+2]The problem, of course, is that fault-current levels are not usually monitored. It is difficult and expensive to tell if a fault was a maximum fault and in general, low-voltage system faults tend to be less than maximum. Therefore, circuit-breaker inspections should be performed according to a plan developed to suit the application. NEMA AB 4-1996 should be referenced for MMCB and ICCB field inspection and maintenance.[/FONT]
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I recommend getting a copy of NEMA AB 4 and reading Clauses 4 through 7, especially sub‑clause 6.6.Introduction?
?and two interrupting tests at maximum short-circuit-current rating. Thus circuit breakers have an extensive but finite interrupting capability, and breakers that experience multiple high short-circuit-current faults should receive a thorough inspection with replacement if necessary.
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It is not intended that molded case circuit breakers be disassembled for inspection. Rather, NEMA AB 4 should be referenced during periodic maintenance or during specific inspection following a high short circuit- current fault. This document is intended to ensure that molded case circuit breakers are well maintained, and provides guidelines for circuit breaker replacement.
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In summary, following an automatic overcurrent interruption at or near its interrupting rating, the condition of any protective device should be checked prior to circuit re‑energization. For molded case circuit breakers, the condition of the circuit breaker is assessed without opening or disassembling the breaker. Circuit breakers that have experienced multiple high short-circuit-current faults, as evidenced by conditions at the source of the faults, should receive a thorough inspection per the guidelines of NEMA AB 4. This document should also be used for recommended, periodic, preventive maintenance.