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Abnormal behavior from [working] voltage detector

  1. Feb 16, 2012 #1
    It is a GREENLEE "GT-11 Voltage Detector" "50-1000V AC CAT IV"

    It has a little plastic encased metal nib on the end and it looks like a fat marker. You just stick it in an outlet and it lights up and beeps to indicate a current. There is no read-out, it just detects.

    Anyway, an outlet of mine hasn't been powering things up. The detector was kind of old, but I just opened it today. Because of all this I have attempted to ensure it works properly - I put it into a socket, and it will go off when I put it in the right side of the socket only. I assume this is normal and that's how it worked on all the working electrical outlets in my house.

    So when I go up to test the 'broken' socket, the voltage detector goes off about 10-15 mm away from the outlet. It will do this for either hole (left or right side), as where with my working outlets in the house it only works when put in the right hole, and it has to be fully inside it. Any explanations as to why the outlet that wont power up anything is detectable farther away?

    Doing all this, I brush up against my 10 year old TV, which is on, and the voltage detector goes off. A few minutes of experimentation-
    it only goes off when TV is on
    it is detectable about 1.5 feet from the front of the TV, and the range grows smaller as you go behind the TV screen. Range diminishes to about 3 inches from all sides of the tv screen once you are on the same plane as the screen.
    After moving the detector about 3 inches behind the tv screen, the voltage meter no longer goes off, and doesn't anywhere else Behind the TV. So the range directly in front of the screen is quite far, grows increasingly smaller until I am on the same 2d plane as the TV screen, then goes away behind the TV.
    Why is anything detectable at all? what is being detected? some increased electrical voltage in the air from my TV? The new LCD isn't 'detectable' by this tool period, just the old tv.

    I also found it weird that some wires, or more like cords (to my vacuum, the first half of my laptop charger- as in the part of the cord that goes from the socket to the power converter block) are 'detectable' when the tip is pressed against the insulated cord/wire. It must be touching it, but the cords are fully covered, and its detectable anywhere along the length of the cord. The cord to my toaster, when on, is not detectable...
    Help me understand this PF? I am fairly positive its not a matter of the detector going haywire. I don't understand some of these detections though..
  2. jcsd
  3. Feb 16, 2012 #2
    Here is a link to the manual for your device. It is a PDF.


    It says "Operation
    The Greenlee GT-11 is useful for identifying hot and neutral
    conductors, finding a break in a wire, and detecting the presence of
    AC voltage at outlets, switches, circuit breakers, fuses, and wires
    and cables,"

    The outlet sounds as if it has a good current though it. Get it fixed. In other words an actual short circuit may be going on there which is a fire risk.
  4. Feb 16, 2012 #3

    jim hardy

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    Walmart sells an outlet tester for about five bucks. Look in electrical section.
    Mine is orange. It's about the size of an ice cube and has three lights on front.
    It plugs into an outlet and the pattern of lights tells you whether the outlet is wired properly.
    It sounds to me like your 'funky' socket has an open neutral, which the Walmart gizmo will detect. (actually it's Hubbell gizmo)

    Many electrical outlets have a labor saving feature on the back. It's a way to save time when wiring a house.
    Instead of wrapping the wire around a screw and tightening said screw, you skin the wire and poke it into a hole in rear of outlet. A spring holds the wire.
    I personally dislike that feature because i've found sockets that lost spring tension then lost electrical connection.

    Sometimes outlets are daisy-chained one after another. Have you any other outlets nearby that dont work , perhaps on a nearby wall in adjacent room??

    So get a tester and check that outlet, and the others nearby.

    On your old TV: be aware CRT's use very high internal voltage to make the elctron beam that draws the picture. That's what your Greenlee is detecting.
    If you stand close to screen and switch the set on, you will feel that electric field tug at the hairs on your arm.

    old jim
  5. Feb 17, 2012 #4


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    These sorts of non-contact voltage detectors detect the RF radiating off the hot leg of wiring--usually at very short distances (usually less than a half cm). As Jim Hardy suggests, a receptacle tester might come in handy:

    However, if you're detecting it at a further distance and on both the longer left prong (neutral) and the shorter right prong (hot) chances are that your receptacle has been damaged (they do fail), or that a leg's shorted on the box (meaning the ground wire, if present, has been disconnected). If you don't have a lot of experience doing this sort of thing (or local regulations / your insurance policy prohibit it), you might want to call an electrician. I'd definitely turn off the breaker / fuse that supplies current to the receptacle before working on it.
    Last edited by a moderator: May 5, 2017
  6. Feb 18, 2012 #5
    Thank you for the replies. I am actually looking more for an explanation of why the air is detectable that far from my TV. I'de say it's obvious that it has to do with the fact it is one of those bigger CRTV's, but why is there so much electrical activity in the air that I can detect it that far away? Also, getting signals when I would put the 'voltage meter' on thick, rubbery plastic coated wires. I would imagine that that would prevent detection. Is electricity escaping outside the wire since I can detect it?

    The TV interests me the most though. How is it making it so I can detect it with this not-so-sensitive 'voltage meter'. Is their more ions in the air somehow? Some particles or energy being emitted that is interacting with the surrounding air? Or is it like some field of it's own and I'm all caught up with the word "air"?

    I tried to google around for a while and couldn't exactly find an explanation. I think I need a real person to connect the various phenomena and produce the correct terminology. I usually can do things like this by myself but I would appreciate help this time.
  7. Feb 18, 2012 #6
    Think more the electromagnetic field around Ac. That is what they detect. That is why it does not have to be in direct contact with the conductor.
  8. Feb 18, 2012 #7

    jim hardy

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    TV has 25,000 volts inside to make the electron beam go. It's pointed at the sreeen...

    Your Greenlee looks for ~ 100 volts at close distance, and the stronger field from your CRT shines farther ..
    Field is measured in volts/distance. 100 volts at 1 millimeter is same as 25kv at 250 mm, not quite a foot.

    That's what i think, anyway. I am not familiar with that Greenlee instrument.
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