120 AC socket and switching questions

Discussion in 'The Projects Forum' started by Sparky, Nov 22, 2010.

  1. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    Greetings –

    I have 5 (somewhat related) questions –

    1) Regarding the AC “socket” with the male pins that are on the back of most monitors and PCs – which pin is the hot and which is the neutral?

    2) I could plug an AC cord up to the socket and if I do this – on a standard male plug that plugs into a wall outlet which of those 2 pins are the hot and neutral?

    3) essentially the same question as 2) on an AC plug that plugs into the wall that has 1 pin that is slightly wider than the one beside it (that won’t plug into the female side of Christmas lights J ) is the slightly wider pin the hot?

    4) How do I call out the simple AC socket found in the back of monitors and pcs? I have searched digi-key and thus far the closest I’ve found is a module with the socket but also with a switch and fuse for around 8 to 9 dollars. I would like the simple socket for cheap.

    5) If switching something on 120 VAC household wiring – light bulb for example – would you switch the hot or the neutral? I’m guessing the hot.

    Thanks
    Sparky
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Pull one from an old computer or misc. other old electronics. You can get old PCs for free.
     
  3. DigitalReaper

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    Aug 7, 2010
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  4. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    Regarding which to swicth -

    Would you switch the hot or the neutral through (for example) a realy to a light bulb?

    Thanks
     
  5. iONic

    AAC Fanatic!

    Nov 16, 2007
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    For an incandescent light bulb it really doesn't matter.
     
  6. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    I understand it doesn't matter electrically -

    I was curious if one method was safer or better practice (or standard practice) than the other?

    Thanks again
     
  7. DigitalReaper

    Member

    Aug 7, 2010
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    Switching the neutral is a bad idea, even if the bulb is off the circuit is still live. Switch the hot wire, or both with a double pole relay if you're paranoid :)
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    In a standard 120VAC light bulb socket in the USA, the outer threaded portion is connected to neutral, and the center is connected to hot (L1 or L2). The hot lead is the one that should be switched.

    On a standard USA 120VAC outlet, the round hole is the ground, the wider flat rectangular hole is the neutral, and the narrower flat rectangular hole is the hot (L1 or L2). For safety reasons, never attempt to force a plug into a socket in reverse.

    Very old lamps or other appliances that have same-width 2 prongs on their plugs should be replaced with modern keyed plugs (one prong wider). If they are old enough to have the same-width prongs, the entire cord very likely needs replacing as well.

    The Neutral wire is only the same as Ground at a single point; inside the breaker panel/fuse box/power distribution panel. Ground is there to protect humans; the ground wire should never carry any current; if it IS carrying current, there is an electrical fault with the device in use. GFCI (Ground Fault Interrupt Circuit) outlets like in the kitchen, bath, and outside, protect against such faults.
     
  9. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    Thanks so much -

    (Kind of what I thought but wasn't sure and I don't do much with household wiring projects)

    SgtWookie - thanks for the information.

    For what it's worth - I have a little embedded project (AVR based) in the works and I have a light buld that will switch on and off as "the example f an event" I will be connecting up to one of the standard white light bulb bases that I've seen used in demonstrations.

    Thanks for the help!
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Consider using LEDs instead of standard light bulbs. LEDs can be very bright, even at low current levels (<20mA), and you can drive them directly using one of your AVR outputs.

    You will need to use a simple current limiting resistor in series with an LED. 220 Ohms would be adequate limiting for just about any LEDs except for infrared (IR) or ultraviolet (UV). Optocouplers use IR diode emitters.
     
  11. Sparky

    Thread Starter AAC Fanatic!

    Aug 1, 2005
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    Thanks Sgt. !!

    Yes I agree an LED would have been simpler (and would have fit on my board).

    Part of this exercise was to demonstrate a circuit that can connect / disconnect household appliances. To keep it closer for the demonstration I'm using a solid state relay controlling the voltage to a standard (Edison style) receptacle and I have a small jumper cable that plugs the 60w light bulb up to the socket.

    -Sparky
     
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