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turn on light, bulb blows, circuit breaker trips - what caused what?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by pc88, May 23, 2008.

  1. Boncuk

    Boncuk New Member

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    indeed!

    :p:p:D:D
     
  2. stevez

    stevez Active Member

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    On a relatively frequent basis I will have a filament failure accompanied by circuit breaker tripping.
     
  3. The Crazy Swede

    The Crazy Swede New Member

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    It just happend to me. (light bulb vs circuit breaker) Re: arcs at 120 VAC; yes, the blue great flash seen when the filament opens, or is open and power is applied is an arc. If you could measure the lumens at that exact point you could determin the current and calculate the resistance. I still can understand after looking at trip current curves of 15 amp breakers how it can trip.
     
  4. dave

    Dave New Member

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  5. mvs sarma

    mvs sarma Well-Known Member

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    There might be hostile atmosphere with heavy lightening etc during this time, over there ?
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When the wrench glows red-hot then there is no arc.

    It takes a high voltage and a gap to make an arc.
     
  7. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You're slipping AG - check the post date, it's months old and already been answered.
     
  8. Willbe

    Willbe New Member

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    Lamps are supposed to have fuse wire inside to prevent the low resistance arc from tripping breakers.
    Maybe the I^2 T curve, the trip curve, of the fuse wire was a few amps to the right of the I^2 T curve for your breaker.

    Arcs have incrementally negative resistance; at some point in the V I curve an increasing voltage causes a decreasing current, but on the whole the V I curve slopes upward and to the right with increasing V or increasing I.
     
    Last edited: Aug 25, 2008
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    There are some extremely cheap light bulbs sold.
    They don't have safety fuses.
     
  10. The Crazy Swede

    The Crazy Swede New Member

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    No hostile weather at time. This is the 3rd time in ten years that it has happend, same fixture subject to vibrations from adjacent stairs. Re: current, the filament does show signs of physical distortion that would indicate high current considering the properties of tungsten. It doesn't make sence but I'm sure the flash seen is from an arc. And Nigel, unless there was a third page in the original discusion, It has not been answered. (If someone wants to talk lead acid stationary batteries, I'm the guy. Charging, step loads, short circuit currents, heat, testing, longevity, etc.)
     
  11. Hero999

    Hero999 Banned

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    Halogen bulbs certainly don't have a safety fuse - they're always tripping the breakers.
     
  12. mvs sarma

    mvs sarma Well-Known Member

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    I feel it is cold filament effect and lack of zero crossing switching of Power supply
    -- to clarify, if the switch on takes at a time the voltage is transiting or is at peak, this cold filament would draw heavy load.
    the circuit breaker(if not thermal) would sense it and trip
     
    Last edited: Aug 27, 2008
  13. neon

    neon Banned

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    What you think and the actuality in the real world are evidently not the same. A wrench across a car battery will actualy exlpode if the conncetion is good. Do you have any idea of a car battery current output during a short across it probably not. a "D" cell can deliver 2 amps try it.
     
  14. Hero999

    Hero999 Banned

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    The short circuit current will depend on the condition and charge of the battery.

    My reasoning was that the battery terminals are normally made of lead which has a higher electrical resistance and lower melting point than a wrench so it's more likely to melt.

    In reality I don't know what would happen because I'm not stupid enough to try it; I take it you've done it before or you wouldn't be so confident in describing it.
     
  15. crutschow

    crutschow Well-Known Member Most Helpful Member

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    One reference says the welding arc voltage is 17 to 45V. And I believe the voltage across a carbon arc lamp is about 35V.
     
    Last edited: Aug 27, 2008
  16. Torben

    Torben Well-Known Member

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    Yep--my welder says 27 volts. I typically weld smaller mild steel so I tend to set it to between 25-80 amperes.


    Torben
     
  17. Willbe

    Willbe New Member

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    Locked rotor current though the starter motor for my '94 Honda Civic is 400 A [@ 4 v across the motor] so the internal resistance of this battery = (12-4)/400 = 20 mΩ, so Isc = 12/.02 = 600 A.

    This should melt #6 copper wire.
    What is the fusing current for a wrench?
     
  18. The Crazy Swede

    The Crazy Swede New Member

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    For example: a group 27 standard GM pick-up batteries short circuit current is around 4000 Amps for 1 second. Car batteries vary in design and are very model dependant.

    Re: #6 AWG or GA. wire melting at 600 Amps...it depends on the time the current flows; it will not vaporize and the motorcycle battery would not be able to sustain a voltage long enough to melt the #6 wire...the insolation on the other hand would melt if it was not made of hapalon.
     
  19. Willbe

    Willbe New Member

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    Which gives 100x the heating effect in a conductor.
    Wear face protection, drop the wrench, post the video!
    :)
     
  20. The Crazy Swede

    The Crazy Swede New Member

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    The resistance of a 6 GA. copper conductor is between .00395 and .000465 Ohms per foot, 12.58 feet per lb (depending on strand count and copper quality.)and the meting point is 1083.0 °C (1981.4 °F) at sea level. The energy required to melt copper is 688 J/g.(g.=0.0022 pound)

    If you know the appoximate length...Bob's you uncle.
     
  21. The Crazy Swede

    The Crazy Swede New Member

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    Battery designs are very differant, a 75 pound battery LA (Lead acid battery) can have 1/16, 1/8 or 1/4 inch thick plates and the surface area of the plates can vary greatly base on the design of the battery. the nominal voltage is usually of each plate is 2 VDC but the short circuit current is really determined by the sum of the surface area of the total number of plates. The short current circuit is supplied by the discharge of the surface of the plates, long rate discharge is dictated by the thickness of the plates of the total mass.
     

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