Light bulb and electric shocks

Discussion in 'General Electronics Chat' started by Thanks4helpin, Apr 1, 2012.

  1. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
    19
    0
    Hi everyone!

    I want to thank all those who answered my other threads. So helpful. I'm so happy to have knowledgeable people dedicating their time to help other newbies. I have a few questions about light bulb and electric shocks.

    1) can you get a shock from a light bulb if you are not changing it? why is there metal on the bottom when it could pose a hazard?

    2) I read on the internet that a shock you get from a light bulb or light switch (say, while touching it with wet hands) is worse than touching a live plug. Is that correct? i'm thinking no because they should be both 120 v (north american standards) but i believe wiki answers said otherwise. then again, i doubt the people there are as knowledgeable.

    3) Is the only 'dangerous' part about changing a light bulb coming into contact with the small metal tip in the middle of the bottom of the light bulb (the only part that juts out the most, around half a cm in diameter) or touching the metal portion of the lamp where the light bulb sits on? I'm assuming it's a small metal portion that only makes contact with the small metal tip. Please advise.


    thanks so much!!
     
  2. evilclem

    Member

    Dec 20, 2011
    118
    16
    1) A light bulb will only shock you if you touch the contactors in the socket (or if you're up to no good and someone turns the light on catching you). Metal is required on the bulb and socket to permit the bulb to work, the bulb not in the socket is safe to touch (although I wouldn't advise doing so directly after unplugging, just incase there's some stray capacitance in there).

    2) The light circuit may not have a safety switch (or RCD), this means that it will not turn off after you touch it. The voltage is the same regardless of the circuit you're trying to get hung up on.

    3) The only dangerous bit is the metal contactors that come into contact with the bulb. Any metal on the exterior of the lamp should be earthed. I would advise turning the light/lamp off prior to changing any bulb.
     
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  3. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    That's only true if the lamp has a polarized plug. And even then, if it were wired incorrectly (easy to do) the outer base conductor of the bulb could be electrically hot if the switch is on.
     
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  4. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
    19
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    so meaning, you could get a shock from a bulb plugged into the socket just by touching any other part this is not glass??
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    If the socket is live, yes.
     
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  6. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    1. If everything is wired to code, touching the metal screw shell of a bulb should
    not give you a shock. It should be connected to neutral, and barring a large
    load on the circuit causing excessive voltage drop, should be close to ground
    potential. Note that this is the ideal world. In real life, things can be
    miswired or wires can get broken, so the screw shell *could* get energized.
    The screw shell is one of the two terminals of the filament. Bipin bayonet bulbs
    (I think they are common in Europe) have the two terminals on the bottom and the
    metal shell is floating.
    2. A 120V shock is the same, regardless of how you are contacting the 120V. Messing
    around with a lightbulb, however, could get you burned from the heat as well
    3. The dangers in changing a lightbulb include burns and dealing with broken glass as
    well. As mentioned in 1, touching the screw shell should not be dangerous in the ideal
    condition, but why risk it.
    4. There's no electrical danger in touching an incandescent or halogen lightbulb that's
    not in a socket. CFLs and LEDs both have electronics in the base including capacitors
    that can store a charge. They should be safe (there are bleeder resistors to drain the
    caps, or they use the switching FET to do so) barring any damage.
    /mike
     
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  7. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    They may be referring to a GFCI plug. A GFCI plug is designed to trip & stop delivering power if someone is being electrocuted. A lamp socket however does not have a GFCI circuit. If you were to put your hand in there, and for some reason were not able to remove it, it could continue electocuting you until you are dead.

    But yes, during the brief electrical shock, the experience would be the same.
     
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  8. Thanks4helpin

    Thread Starter New Member

    Mar 14, 2012
    19
    0
    Thank you everyone for your kind help.

    sorry I am unfamiliar with the types of lightbulb and terms used in some of your answers. For example this lightbulb shown attached - it is a halogen or CFL lightbulb? or some other. The socket that it fits on is a long light structure above my bathroom mirror. If you were to put one end of this light in, and touch the other end of this light with your finger, will you get a 120 shock? does it matter whether you touch the left or right end?

    I assume that if you just touch both of the metal parts of the socket clamps, your hand would act as the 'lightbulb' and the current would go through you, all 120 volts?

    In which of these situations would you get the most shock? or would it be equal it is 120 volts no matter what.

    Assume in all these situations the switch is on.

    Thank you so much again! Because of all your help my anxiety has much decreased. Really appreciate it, and don't worry I'm not trying this at home. But as I mentioned earlier, have OCD and get very anxious when I'm unable to find out something that is severely invading my mind.
     
    Last edited: Apr 18, 2012
  9. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    That's a halogen bulb. It can shock you if you hold one end while the other is in the socket. Halogen lamps are infamous for burns and fires but they're safe in well-constructed fixtures.
     
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