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Defective Bulb Tripping Ckt Breaker: How Possible ?

Discussion in 'Electronic Repair' started by Robert11, Oct 31, 2006.

  1. Robert11

    Robert11 Guest

    Hi,

    Boy, this is a funny one.

    Wife turned on a hall light switch last night, big flash by one of the hall
    lights, and the ckt breaker tripped.

    Was about 2 days since putting in a new bulb there.
    Was the el-cheapo brand picked up at CVS, and made in China.

    Replaced the bulb with a GE one, and so far everything seems O.K.

    Question: I can't imagine how anything, like e.g., a broken filament
    perhaps, can short out the circuit.
    But, perhaps ?

    Can anyone think of a bulb failure mechanism that might trip the breaker ?

    Or, might this be just a coincidence ?

    Thanks,
    Bob
     
  2. This often happens. It's because when the filament breaks, it falls
    across part of the wire nearer the mounting points, thus horting them
    out. That's why there's a bright flash, and the fuse/breaker goes
    because of the increased current through the much lower than normal
    resistance.

    --

    rgds
    LAurence

    ...."I forgot to increment the counter" said Tom, nonplussed
    ---*TagZilla 0.059* http://tagzilla.mozdev.org
     
  3. Meat Plow

    Meat Plow Guest

    Might have a problem with the base of the bulb or the socket.
     
  4. N Cook

    N Cook Guest

    I'm only going by memory and may have it a bit wrong.
    A tiny part of the filament wears to the point it creates a hot-spot which
    rapidly gets worse causing the first part of the intense flare. In that
    super-heated process a plasma state is formed within the bulb. In a plasma
    state the effective conductivity across the 2 filament suspension end points
    becomes orders of magnitude less than the original filament resistance so
    for very short duration , can pass tens or hundreds of amps.
    It is the same mechanism whereby a lightning discharge through air can pass
    millions of amps through a channel that is only about 1/2 inch in diameter
    which no metal could pass. The same discharge passing into the right soil/
    conditions leaves a yards long but same 1/2 inch wide hollow tube punched
    through the ground, see keyword fulgurite.
     
  5. Sure. There should be a fuse in one of the leads inside the bulb, but China
    ???
     
  6. Yukio YANO

    Yukio YANO Guest

    This all sounds nice BUT the two strands of the broken filament limits
    the current to ~ current to less than 1 Amp. !

    More likely the Light-bulb in question was mounted Socket-Down and a
    portion of the broken filament dropped down and shorted across base
    conductors. The short length of filament's Resistance would be much less
    than the nominal ~ 200 ohms of the intact filament. The resulting arc
    would vaporize in the Argon Gas of the light-bulb and create a miniature
    MIG (Metal Inert Gas)Welding condition at which time, the Circuit
    Breaker would Open due to the excessive current draw. A photographic
    Flash-bulb would be a good analogue. Source Impedance and Current
    Limiting of Household wiring were engineered to safely harness
    electrical energy!

    Yukio YANO
     
  7. Have you recently changed from fuses to circuit breakers? A bulb blowing
    and tripping one isn't uncommon.
     
  8. Lionel Sharp

    Lionel Sharp Guest

    G'Day

    This has happened to me. The bulb was a "Reflector Lamp Type R80" with
    an Edison Screw Base". It was used in a "down light" and they have a
    very short life (6 months or so). In the process of removing it the
    brass base and the glass globe separated and I had to get the base out
    of the socket (with power turned off of course.) with a pair of pliers.

    Recently purchased a couple of bulbs from China and on the side of the
    box it says:-

    For your added safety every globe has 2 built-in safety fuses.

    Seems like the some manufacturers are aware of this problem

    Lionel L Sharp
     
  9. James Sweet

    James Sweet Guest


    This is common, the filament breaks and an arc strikes in the fill gas
    between the ends, this quickly vaporizes what remains of the filament
    and will sometimes melt a good portion of the filament support wires
    before the fuse in the stem blows. If the fuse is poor quality or not
    present (as may be the case in a cheap import bulb) it can easily trip
    the circuit breaker. This arcing is what kills most dimmer switches and
    touch lamps, the triac is destroyed before the fuse can react.

    This is one more thing I like about compact fluorescents, when they fail
    they don't blow with a bright flash and a pop which is always a
    startling experience when you flip on the only light in a dark room.
     
  10. Meat Plow

    Meat Plow Guest

    I saw flames shoot out of the side of the base of a screw in fluorescent.
     
  11. Right, they blow with a considerable BANG and a bad smell. The CFL in
    my wife's bedside lamp did that. Of course I had to open it up and see
    what happened. The first capacitor of the voltage-doubler ( a tiny
    10uf cap ) had popped. Really popped. It spread black goo all over
    the insides of the thing.
     
  12. Plasma, most likely, from the internal arc. Light bulbs are filled
    with argon gas which can conduct quite nicely once started.

    Or the floppy wire ends had enough magnetic attraction to attract each
    other, which makes the field stronger, attracting each other some
    more...
     
  13. James Sweet

    James Sweet Guest


    Interesting, well I suppose it could happen, in 8 years of using them
    almost exclusively mine so far have all just failed to turn on, save for
    one that made a soft buzzing noise and let out a puff of stinky smoke.
     
  14. Meat Plow

    Meat Plow Guest

    Also could have caused a momentary neutron star.
     
  15. default

    default Guest

    Happens more than a lot - depending on the circuit breaker.

    Magnetic beakers trip faster than thermal ones.

    Filament opens - the tungsten is in a partial pressure of nitrogen as
    a rule - not a vacuum just inert gas at low pressure. The filament
    separates and sparks an arc in the bulb. The ionized gas is a dead
    short.

    Low pressure gas conducts electricity better than high pressure gas -
    until you start approaching a total vacuum. Ionization gauges are
    used to monitor vacuum pressures in lab instruments - put 200+ volts
    on it and it conducts until you get to near perfect vacuum.

    That failure will trip a magnetic breaker and not phase a totally
    thermal breaker - event is over before the breaker heats.

    Solid state relays are toast - if they drive an incandescent lamp that
    opens.
     
  16. Sjouke Burry

    Sjouke Burry Guest

    The filament in the bulb vaporises at the point
    where it breaks, and produces a nice hot plasma
    and a dead short across the input.
    If you want to see such a plasma cloud, put a
    defunct bulb in the microwave oven(for a few seconds
    only).

    That in turn can vaporize the connections
    to the base of the bulb.
    I have had lamps producing a pop sound close to
    an explosion that way, and sparks flying.
    On checking, the base of the lamp was looking burned
    around the attachment point of one of the wires.
    It works much better with 240 Volts :) :)
     
  17. Eeyore

    Eeyore Guest

    Yup.

    If there's an arc, which it sounds like, that has negative resistance and the
    fault current can be very high.

    Graham
     
  18. You've got it about right. And in response to the other post, it's
    rarely a matter of the filament falling across the terminals.

    http://members.misty.com/don/bulb1.html#wbs

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
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    Important: Anything sent to the email address in the message header above is
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  19. Nope, he's got it right. Once the arc forms, it may not stay between
    the broken ends. Because the arc is a negative resistance, increasing
    the current lowers its resistance. So, it can grow towards the ends of
    the filament in an instant and then it's nearly a short circuit.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  20. But they may blow with a puff of smoke and a acrid smell.... :)

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
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