5

I have a light switch in my building that frequently gives me a "shock" when I push it. The shock seems to come from the two mounting screws. It has a photoelectric sensor that turns the light off when I'm not in the room - I don't know if that's important.

  1. Using home inspection tools readily available, is there a way to determine if this is a grounding problem?
  2. If it is a real problem, what resource should I consult to figure out a way of repairing the problem?
  3. If I can not find a grounding problem, are there other reasons besides grounding that might cause this phenomenon? What professional resource should I utilize for a diagnosis if the problem does not appear to be grounding related?

migrated from engineering.stackexchange.com Dec 11 '15 at 17:10

This question came from our site for professionals and students of engineering.

  • Mark - this seems like a great question for DIY. I noticed that you have an account there. Was there a particular reason you asked this question here on Engineering instead of on DIY? If you'd like, I'd be happy to migrate this over to DIY for you. – GlenH7 Dec 10 '15 at 18:28
  • The question was posted here as I wasn't sure if it belonged to DIY or Engineering - I'm not an expert in Electrical Work, and the Building is a Commercial Building - not my home. So I wasn't going to DIY - I was going to hire someone, but wanted to investigate the costs. I don't know if that changes anything. – Mark Dec 10 '15 at 21:25
  • Whether the building is commercial or residential shouldn't really make a difference w.r.t. a simple light switch, even an energy-saver switch like this. – Air Dec 11 '15 at 0:55
3

I'd get yourself a non-contact voltage tester:

NCVD

These will only light up when it's right near something hot. Test it to make sure it's working by putting it in an outlet:

Testing recep

Make sure it's lighting when it should. Then, touch the screws with it. If the NCVT lights up (and stays lit) when you touch it to the screws, they're hot. If it flashes very briefly, that's static.

If it's hot, cover them with electrical tape until you can address the problem.

If you want to turn off the breaker, inspect the connections inside the box, and see if you see anything that looks wrong, that's not easy enough to do - if you have a basic understanding of how to work safely with your electrical, and how the connections should look.

If you're comfortable replacing the switch with a new one, that is an easy test. (You can use an inexpensive switch, no occupancy sensor, to see if the wiring is sound.) You could test the possible bad switch (disconnected from wiring) with a continuity tester to see if the switch is defective.

But it may be best to just turn off the breaker and call an electrician.

7

Typically the metal screws in the face plate/trim of a home electrical device (outlet, light switch, etc.) attach to the electrical device itself. This, in turn, should be grounded.

To address your question in general (the spirit of what you're after):

If it only shocks you one time, which is to say if you touch it and it shocks you, but subsequent touches without moving don't continue to shock you, then I would say that you are getting a static electricity shock because the screws in the trim plate are grounded and you are not. This would be more likely if you have carpet, the air is dry, and/or you are wearing clothes that are wooly and/or you don't use dryer sheets.

If you get shocked (badly - shocks from 110 HURT!), and every time you touch the screw you get shocked (badly!), then you have a serious problem and should contact an electrician.

Most likely, though, you're just experiencing drier air because Winter's coming and the dew point is dropping while your interior temperatures are staying relatively constant. Every winter every outlet in my house shocks the **** out of me. But only the first touch. Subsequent touches don't do anything because I discharged my static buildup.

To answer your numbered questions:

  1. Turn off the breaker to the offending outlet, remove the trim screw, remove the retaining screws that hold the device into the wall box, then pull the device out. Check for problems with the insulation - you may find these where the cable enters the junction box - and for bare wire ends touching the junction box. If you have a multimeter (not sure if most people would consider this a common household tool, though it should be!), then you can try turning the breaker on and measuring voltage between the ground wire in that device to ground in another outlet.

  2. If there is a real problem, contact a licensed, bonded electrician. You may need new wiring pulled to the offending device if the insulation is frayed/nicked where it enters the wall box.

  3. Yes, other things can cause you getting shocked - primarily the fact that the outlet is grounded correctly. Though I suppose maybe if your building has a ground wire that isn't grounded, and the thing that's shocking you is a doorbell or something else outside, and you're standing in a puddle, and that is when you get shocked, that maybe you're getting shocked by some piece of deranged (damaged and/or improperly grounded) piece of equipment somewhere else in your building that is powering the ground wire. But, in this case, the ground wire would have to go nowhere, else the deranged equipment would be safely handled, which is the point of the ground wire.

Anyways, like I said, ultimately the shocks are (annoying but) one-time events that don't hurt that bad and are nothing to worry about, or they happen repeatedly and hurt very bad and you should contact an electrician.

1

It's not clear from your question whether it's a plastic switch with metal screws or all metal (or what country you're in). I'll assume the former - plastic switch - metal screws.

It sounds as though there is a metal box behind the switch and that somehow this is live or there is a low enough resistance between live wiring and the box or conduit to make it live.

Any metalwork like that should be earthed properly. Take off the switch (with power isolated) and inspect the box and any earth connections and look for broken insulation. Then, with care, turn power back on and check for voltage on the box.

  • Switches with sensors typically draw a bit of current even if the lights are off. That may explain where the energy is coming from. – GlenH7 Dec 11 '15 at 16:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.