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Why circuit breaker shuts off when lamp burns out?

  1. Apr 18, 2012 #1
    Isn't the case that when the lamp filament melts the resistance of that part of the circuit goes to infinite? So why does the circuit breaker turn off current?
    Thank you
    Regards
     
  2. jcsd
  3. Apr 18, 2012 #2

    Bobbywhy

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    The answer to your first question is yes, when a lamp filament melts the lamp's resistance goes to infinity (open).

    Now, to answer your second question will you please describe where is the circuit breaker? What equipment is this? We can't know why the CB trips until you tell us the details.
     
  4. Apr 19, 2012 #3

    jim hardy

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    from http://www.megavolt.co.il/Tips_and_info/incandescent.html

    see also this informative diagram

    http://www.dumet.net/lamps.html
     
    Last edited: Apr 19, 2012
  5. Apr 19, 2012 #4

    Bobbywhy

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    Thank you, Old Jim. Never imagined that arcing scenario drawing hundreds of amps and tripping the breaker!

    Us old dogs CAN learn new tricks!

    Bobbywhy
     
  6. Apr 19, 2012 #5

    jim hardy

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    Thanks for the kind words Bobbywhy !

    I have to think the hundreds of amps scenario is the exception.
    I've only seen two lamps blow their tops off. But we all know that "flash-thud" when they go.

    I didnt know about the internal fuse until found that link. A good reason to buy the $1.59 lamp instead of the $0.49 for locations where falling glass shards could be an annoyance..

    but the point is, an arc conducts well. Only after it goes out do you see infinite resistance. That should be at next zero crossing of sinewave.
     
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