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While reaching behind a desk in my office, I leaned against the wall and felt a pinch on my shoulder. I realized I was leaning on the lower screw of the light switch and thought it had a metal burr or something sticking out. I touched the screw with my hand and felt electric current flow through my hand. I tried it again a few minutes later and felt no current.

I'm going to call an electrician ASAP but was curious, what could be causing this?
My house is 58 years old and the wiring is probably that old as well.

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Were you touching anything metal or standing barefoot on concrete? Was it an actual painful shock or tingling? –  Grant Aug 24 '13 at 3:43
    
I was standing barefoot on the hardwood floor. The house is on a raised foundation over a crawl space. It wasn't a painful shock, just that tingling sensation that feels like your muscles are vibrating. –  Sam Aug 24 '13 at 8:37
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It may be that if you were well grounded (barefoot on wet concrete) you would have gotten a serious shock with enough current to potentially kill. That can happen if the metal box behind the switch is NOT grounded AND the HOT wire is electrically contacting that box. But it can also happen with capacitive interfacing (wires near each other) in a way that would cause little or no current. But you don't know what the problem is, so be careful. Let the electrician figure it out and fix it. –  Skaperen Aug 24 '13 at 21:20
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3 Answers

up vote 2 down vote accepted

There are (at least) three possibilities:

  1. Static electricity.
  2. Current flow to something grounded
  3. Capacitive flow.

Most everyone is familiar with static electricity I think. Sparking to a properly grounded electrical box is to be expected. Static charge can be built up and stored on your body in many way, like rolling acrylic wheels of a desk chair across the floor. Or walking on a carpet. After being discharged, if you don't build up another charge, then there is nothing to discharge, so you don't feel anything.

For there to be current flow, there would have to be a potential. It is possible (though unlikely) that the light switch is mis-wired and presents a potential to the screw. If you touch it while also touching something grounded like the desk, a land-line phone, etc. then an electrical path exists through you. If you are not grounded, like when you repeated touching the screw, there is nothing to feel.

A capacitive path is even less likely than the second possibility. I am only aware of it under high voltage situations, such as this video of a flying helicopter being bonded to high voltage. It is current flowing each a.c. cycle back and forth and stored in a conductive object. It stands to reason that if huge sparks occur at, say, 200,000 volts, that a small version could occur at 120 volts using your body as a capacitor. If you are sensitive enough, you might be able to feel it. However, if you use a less sensitive part of your body, then maybe you wouldn't. Electrical sensitivity could well vary millimeter by millimeter across a fingertip. This explanation also requires that there be an (erroneous) potential on the light switch screw.

If the second or third situations exist, there is a wiring fault, so it is good an electrician will be checking it.


Just thought of another one:

A fourth possibility is that there is a strong radio transmitter near by. The capacitance of your body is more of a factor at higher frequency. Maybe you would feel it sometimes but not other times because the transmitter is not continuously on. There isn't really much to do about it.

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Can static electricity be discharged by a tingling sensation? I'm used to feeling a shock and a spark when discharging static. –  Sam Aug 24 '13 at 8:39
    
@Sam: Sure, especially low levels of static like might occur while one is being discharged continuously at the same time static is being generated. –  wallyk Aug 24 '13 at 16:02
    
@Sam What you've described is almost certainly not static electricity. It's most likely, as Grant described, improper grounding –  BlueRaja - Danny Pflughoeft Aug 26 '13 at 9:28
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I have had this happen when touching two items that were both grounded, but not bonded properly. I used to get it when touching any cable tv coax cables in the house. The cable company hadn't installed a proper ground to the water pipes. If I touched the cable and anything connected to the electrical ground I would get a tingling feeling. Sometimes a painful one.

This happens because ground isn't an absolute voltage. Ground at my electrical panel and ground on the pole the cable company used differ by enough to be felt. This can be dangerous if there is a big enough difference.

Check that all cables for TV and phone and such are properly grounded.

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that age home probably does not have ground rods. those days grounds and neutrals tied together in main panel. ccode says two 8' less than ten feet apart tied together then connected to ground strap (existing or added) in main panel. then if need be separate neutral and grounds in panel. doing all this with main circuit breaker off!!! white neutrals connected to service bare cable.

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