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Thread: Why a small shock through a switch that was off?

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    DIY scratch-pad engineer leejosepho's Avatar
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    Default Why a small shock through a switch that was off?

    I just added a new circuit in my basement, and I am sure I did everything correctly. I ran Romex to a junction box, then wired down to a switchbox box with two switches. One of the switches is lighted when off, and I had the power on while attaching its single light a few feet away ... and I got a very slight shock between the bare ground wire and the black while stripping the end of the black wire. With the box grounded, the switch was lit up while the run to the bathroom light was still completely open, and I had assumed no power would be coming through the switch while it was off. So, what caused that bit of current that gave me a slight tingle? What I felt was so light that I first thought it was just from my arthritis or whatever while squeezing the wire strippers.

  2. #2

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    Unless the circuit is shut off, all switches have power to them whether they are on or off. The power is always there waiting to be sent to the fixture.
    http://www.inspectpa.com/forum/forum.php
    My answers are based mostly on the ICC codes. Advice given is my personal opinion and every person performing work should acquire a permit from his/her jurisdiction and get the work inspected. My opinions are not directions to follow for DIYs or professionals

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by leejosepho View Post
    I just added a new circuit in my basement, and I am sure I did everything correctly. I ran Romex to a junction box, then wired down to a switchbox box with two switches. One of the switches is lighted when off, and I had the power on while attaching its single light a few feet away ... and I got a very slight shock between the bare ground wire and the black while stripping the end of the black wire. With the box grounded, the switch was lit up while the run to the bathroom light was still completely open, and I had assumed no power would be coming through the switch while it was off. So, what caused that bit of current that gave me a slight tingle? What I felt was so light that I first thought it was just from my arthritis or whatever while squeezing the wire strippers.
    Current flowing through the pilot light on the switch

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by jwelectric View Post
    Current flowing through the pilot light on the switch
    I suspected that, but I would think "off" would actually mean "off"!

    So then, there is always some current flowing through the light bulb on down the line even when the switch is off and even though the pilot circuit is already complete through the grounded switchbox?

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    Never assume my friend.

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    Plumber Cass's Avatar
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    Were you using uninsulated wire strippers?

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    Plumber jimbo's Avatar
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    Quote Originally Posted by leejosepho View Post
    I suspected that, but I would think "off" would actually mean "off"!

    So then, there is always some current flowing through the light bulb on down the line even when the switch is off and even though the pilot circuit is already complete through the grounded switchbox?

    The pilot circuit is NOT completed through the ground connection. It is never allowed to run any current to ground. The small current used for the pilot flows through the circuit load (light bulb, or your body!).

    This is why switched like that will often cause flakey operation of fluorescent bulbs ( flicker, etc).

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by jwelectric View Post
    Current flowing through the pilot light on the switch
    Yes. The 1 mA that passes through a neon lamp is just perceptible.
    I don't think most phantom voltages can deliver enough current to be sensed, unless you got the shock at the end of at least 200' of Romex.

  9. #9
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Cass View Post
    Were you using uninsulated wire strippers?
    No, but I was touching some of their exposed area.

    Quote Originally Posted by jimbo View Post
    The pilot circuit is NOT completed through the ground connection. It is never allowed to run any current to ground.
    I understand, but it did first light up even before the fixture and bulb had been attached ... yet now the pilot goes out when the bulb is removed from the fixture at the end of the line. Go figure, eh?! Overall, it just surprises me that "off" does not always really mean "off"!

    Quote Originally Posted by Thatguy View Post
    I don't think most phantom voltages can deliver enough current to be sensed, unless you got the shock at the end of at least 200' of Romex.
    The shock (barely a tickle) was at the end of a 35' piece, and now that I see the switch's pilot goes out when there is no bulb at the end of the circuit, everything seems fine.
    Last edited by leejosepho; 12-22-2008 at 04:02 PM.

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    Plumber jimbo's Avatar
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    I disagree that this would be referred to as phantom voltage. It is real voltage. There happens to be a high resistance in series, which limits the current which can flow through your body.

    This probably also reinforces the idea that a switch should not be relied on as the means to remove power from a circuit prior to work.

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