How do I test an outlet with a multimeter?

Discussion in 'Homesteading Questions' started by canfossi, Feb 27, 2011.

  1. canfossi

    canfossi Well-Known Member

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    I have an outside GFI plug that isn't working. I have pressed the reset button and still nothing. The circut breaker at the panel is fine and I have put the two probes from multimeter into the plug and I get a reading of zero. The multimeter was on the right setting to measure the AC current. I am wondering if there is a problem with the actual GFI receptacle. So if I pull the plug out from the receptacle box, can I test if there is current coming out of the actual wires (black and white)? How do I do this with the multimeter and do I keep it on the same setting as before, also what kind or reading should I get if everything is fine there, 120 volts? I am a bit of a novice when it comes to electrical, but would like to at least check if there is power from the wires. Hope you can help, thanks! Chris
     
  2. deaconjim

    deaconjim Appalachian American Supporter

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    Put your meter on ~Volts (~ means A/C) on the lowest range greater than 120 volts. Test your meter on an outlet that you know is working by putting one lead in each of the flat holes, being careful to not touch the metal part of the leads. Watch the meter display for the proper voltage reading (it should show between 110-130 Volts). Move to the outlet you are testing, and repeat. If you do not have voltage on the suspect outlet, pull the outlet cover off and check for voltage on the wires where they connect to the terminals. After you have tested that outlet, go back to the known good outlet and check your meter again.
     

  3. texican

    texican Well-Known Member

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    I'd check the grounding wire from the gfci circuit back on the panel first. Of course, taking the cover off the panel box and 'investigating' will get you kilt if you double dog sure don't know what your doing. Sometimes, even if you 'know' what your doing.

    If you're going to pull the gfci, you also need to be extra careful... if there is voltage coming to the gfci, the wires'll be hot, and will bite you. If you have a metal box it's in, I'd wear rubber gloves... I hardly ever can get a receptacle to come out of a metal box without getting 'sparks'. I'd turn the circuit breaker off, before pulling the actual gfci. Once it's out in the open, flip the breaker and then check for voltage. If bad, replace.

    Remember the old saying... There are two things in this world that'll kill you dead... Messin' around with another mans wife, and messin' around with electricity.

    I have had to replace gfci's before... prefer gfci circuit breakers... easier to deal with.
     
  4. canfossi

    canfossi Well-Known Member

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    Yes, I'll switch off the power before I pull out the GFI, then turn it back on to test. So I just put one probe on the black wire and the other probe on the other white wire? The multimeter has a black probe and red probe, does it matter which one goes to the black wire and which one goes to the white wire to test? Or do I put both probes on the black and then both probes on the white wire? Thus if I get a 120 volt or thereabouts reading while touching the wire that will tell me that the problem with with the actual GFI not the power going to it, correct? Thanks Chris
     
  5. artificer

    artificer Well-Known Member

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    The colors with AC power are typically:
    white = neutral (this is connected to the ground at your main service entrance/panel)
    black, red, blue = hot

    DC power colors are:
    black = ground
    red = +volts

    For AC, it doesn't matter which lead goes where. For DC, it does, so they are colored red/black.

    Once you have safely exposed the wires going into the GFI, turn power/breaker back on. Set the multimeter to AC (~volts), and put one probe on each of the wires going into the GFI (white and black) at the same time. If you get the 120V reading, then power is good to the GFI. If you get no voltage, then something is wrong with the house wiring.

    If power is good to the GFI, and you've hit the reset button, and still don't get voltage at the GFI, then its dead. Its fairly common for them to die, and you just replace them.

    A GFI will work withou a ground wire. Its one of the uses for them. Its better to have a good ground, however.

    Michael
     
  6. Jim-mi

    Jim-mi Well-Known Member

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    For AC it makes no difference what probe goes on the 'black and white' in the box.
    One probe must go on the black & and one on the white........

    If in dought PLEASE get some help.........

    Like Tex says it is very easy to get badly bit when working on those darn GFI's
     
  7. Nimrod

    Nimrod Guest

    Assuming that the outlet worked fine before you had problems and the reset button resets the outlet, you could have a bad outlet because (1) One of the wires is loose at the outlet or at the other end, usually another outlet or (2) the outlet itself has gone bad. It's also possible but very unlikely that there is a break in the wire between the outlet and whatever it comes off of.

    It sounds like you have already tested to see if there is power at the outlet and there is not. Turn off the power at the breaker, undo the 2 screws that hold the outlet into the box, pull the outlet out of the box, keep the wires attached but make sure the bare part and screws don't touch anything, leave the outlet hanging out in space by the wires, turn the power back on, carefully touch you multimeter leads to the screws, one to each screw on either side of the outlet and nothing else. Do not touch the screws or the bare part of the multimeter leads with you hands or you could get zapped. One screw should be brass colored (hot or black wire), the other is silver colored (neutral or white wire). There is also a green screw on the top or bottom of the outlet with a bare or green wire attached. This is the ground which would be at fault only if the outlet wouldn't reset. If your multimeter shows about 110 volts it could be the outlet or the connection to the outlet. Turn off the power at the breaker and redo the wireing to the outlet. Turn on the power and retest the plug holes in the outlet. If there is power, problem fixed. Turn off the power, screw the outlet back in the box, put on the cover, and turn the power back on. If the multimeter doesn't show voltage go back to the box where the wire to the outlet comes from, turn off the power at the breaker, redo the wireing, turn on the power and retest at the plug holes on the GFI breaker. If power, problem fixed. If no power, turn off the power at the breaker and replace the outlet.
     
  8. tiogacounty

    tiogacounty Well-Known Member

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    Just as a general note here. The failure rate of GFCI receptacles is absolutely astounding. Last year I had two out of the same case that were defective. They are designed to "fail-safe" meaning that they will not reset if they have suffered a failure. I no longer by the Levition brand due to repeated failures. The best way to test a GFCI is with a cheap outlet tester. You plug it in and it will tell you if the outlet is wired correctly and is properly grounded. You press a test button and it tests the GFCI.
    The one I use is an "Ideal" brand and they run $8 at Home Depot or Lowes.
     
  9. Oldcountryboy

    Oldcountryboy Well-Known Member Supporter

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    I'm probably too late unless your still having problems. You should be able to check the side terminal screws without removing the GFI from the box. If there is no voltage then check from each terminal screw to ground to make sure there is no voltage again.

    Reason for this is just incase each terminal has 110v and coming from the same power leg, then it will register as having no voltage when you actually have voltage. If you accidently touch one of the terminals and touch ground at the same time you will get zapped. So its always safe to be sure you check from each side to ground.

    Once you have determined there is no voltage, carefully remove the screws holding the GFI device in and then gently pull the GFI out of the box. Once you have it pulled out far enough you can use a screwdriver to unscrew the terminals. When the terminals are unscrewed the wires will slide out of the back. Now double check these wires for voltage , from white to black and from each white and black to ground. If no voltage your problem is somewhere else. If you have voltage, then you probably need to replace the GFI.
     
  10. canfossi

    canfossi Well-Known Member

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    Thanks everyone, doesn't sound too difficult. It's raining today so I will check it tomorrow. Thanks again, Chris
     
  11. Shrek

    Shrek Singletree Moderator Staff Member

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    Rain, electricity and tomorrows to do list___a very wise combination.