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Thread: Circuit breaker did not trip why?

  1. #1
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    Question Circuit breaker did not trip why?

    Went to a customers house because he smelled burning plastic in the garage.
    Opened up the panel and found that the 2 pole 30 amp circuit breaker that powers the pool equipment was charred. The back of the breaker was burned badly. Also a couple of the surrounding breakers were charred. My question is why did'nt the main breaker trip to protect the buss bars? Why did'nt the 30 amp breaker trip? This home is not that old probably built around 1995-2000. 200 amp Siemens panel with a 200 amp main breaker. Anyone seen this before. Thanks for your feed back.
    Licensed Electrical Contractor
    Dallas,Texas

  2. #2
    Quote Originally Posted by hotblueelectric View Post
    Went to a customers house because he smelled burning plastic in the garage.
    Opened up the panel and found that the 2 pole 30 amp circuit breaker that powers the pool equipment was charred. The back of the breaker was burned badly. Also a couple of the surrounding breakers were charred. My question is why did'nt the main breaker trip to protect the buss bars? Why did'nt the 30 amp breaker trip? This home is not that old probably built around 1995-2000. 200 amp Siemens panel with a 200 amp main breaker. Anyone seen this before. Thanks for your feed back.
    It's unlikely the main would care this is happening. And actually, you can have alot of arcing on loose buss connection that is well under 30 amps. The breaker will not care. Motor runs,,,normally draws 20 amps(for example),,,,,bad buss connection,,,arcing,,,,burning,,,,still only drawing 30 amps(for example),,,,,,,You don't think that's possible?

  3. #3
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    Those breakers did not trip because there was no overloaded or short circuit.

    You had a loose connection and/or bad breaker. The breaker literally cooked itself from the inside-out, due to the bad connection(s). :mad:

  4. #4
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    I agree, sounds like a loose connection. Customers always ask me the same thing when I find receptacles burned up due to a loose connection and the breaker didn't trip.

  5. #5
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    Ok, so then with a loose connection and arching amperage can still be below the threshold of the circuit breakers capability (80%) and not cause it to trip.
    Licensed Electrical Contractor
    Dallas,Texas

  6. #6
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    If the arcing was at the bus, the 30 amp circuit breaker does not see this. It would take heat at that point to open the circuit breaker. That condition was on the supply/line side of the circuit breaker.

    It was most likey a glowing arc, which the main would not pick up, as there is an intermittent factor that keeps the level low enough the main breaker did not see it. That is one of the features of Arc Fault Circuit Interrupters - these types of circuit breakers can see arcing faults at a much lower level than standard circuit breakers can.
    Instructor, Industry Advocate

  7. #7
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    Normal breakers like a main or feeder breaker do not "see" or analize anything - they are dumb as posts... It doesn't know anything... It takes some specific conditions for it to even open for a short circuit or over-load. Take a look at the trip curves of some and you might be surprised what it takes to trip one... And that is only on the load side of the breaker... A 200A main could hold nearly ~150% (~300A) of the rating for over two hours...

    In the case of the OP - it very well couldve been dirt or sheet-rock dust on the buss....
    Electric heretic
    It's always gonna be in the last place you look....

  8. #8
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    Many years ago I witnesses a overcurrent device on the POCO transformer trip before the 200A Main Service Breaker did. The enclosure with the 200A breaker was glowing green inside. Light was coming out of every crack. The overcurrent was on the load side of the 200A breaker. The disc in the meter base looked like a 78RPM record.

    Most people think that circuit breakers will protect them from anything that can go wrong with an installation. Big mistake.

  9. #9
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    Before you know it, these breakers will be able to protect you against identity theft! I definately like arcfault breakers! Yes they have their kinks but all in all they will save lives. Sometimes it seems like big industry is in the codemakers pocket but Im starting to believe these people know what their doing!
    Last edited by aelectricalman; 12-15-09 at 09:47 PM.
    Chris Hill, EE,ME,GA-CR
    Power Factor Correction

  10. #10
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    Anyone seen this before
    All the time. Usually with A/C breakers (in the desert)

    Stuff happens.
    Disclaimer: The opinions expressed here are solely mine and do not necessarily reflect the views of other members of this community. Do not misunderstand them as an encouragement to violate the NEC. Also, don't forget that the NEC is not necessarily the AHJ.

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