What causes this kind of electrical problem?

May 14, 2008 9:14 AM

What electrical misconfiguration would cause there to be enough current to give a mild shock when the screws going into a switch plate are touched -- yet not enough of a problem to pop the circuit breaker?

I know I'm supposed to get an electrician. However, I'm in a rental house and I want to educate myself so that whoever gets sent out here diagnoses the problem correctly.

Basically there's current coming through the screw to the gang box, the light works, and the circuit breaker is not popped.

I figured it might have been a hot wire touching ground (gang box) but I would assume that would trip the breaker. Interestingly this switch and the outlet it feeds went dead this morning (circuit breaker still untripped) and no longer works, but the wiring problem is still there I'm sure.

posted by tinkertown to home & garden (7 comments total)

The screws are carrying full line voltage. The reason you get only a mild shock when you touch them is that you are very weakly grounded. If you were touching a good ground, you could easily be killed. Get a professional electrician to fix it NOW.
posted by KRS at 9:37 AM on May 14

First: Turn off the breaker and wait for help.

It does sound - off the cuff - like a hot leak to ground or an open neutral.

The breaker not tripping is not unusual or indicative of a problem, not enough current was drawn on the leak to trip it. A normal breaker is not designed to protect you from shorts or leaks to ground. It is to trip when the current drawn through a wire exceeds limits that would melt it or ignigt fire in the insulation, it shuts down TO PROTECT THE WIRE FROM BURNING, not to prevent the current from killing you. So you could have a leak to ground or an open neutral and the breaker wont trip until so much current runs through it, many times the current needed to kill you. A GFI (GFCI) breaker is designed to protect you from harm.

Anyway your possible issue: the ground may be broken between the leak and the panel, in effect isolating the box and device, so the only pathway for the current to ground is through the device to the screw and then through you.

The electrician should of course check for a loose hot leg but also for a proper pathway of a ground from the device (switch/receptacle) to the breaker panel and beyond but...

Also iy is also possible that there is no proper ground at all and instead the neutral is loose, which might explain why the devices dont work and the current wants a path to earth through you.

An electricain should know this right off, it is pretty common: possible loose hot leg, possible loose neutral, ensure proper path to ground.

Good luck.
posted by Kensational at 9:46 AM on May 14 [1 favorite]

I'm not really familiar with the US electrical system but if it's similar to other places then I'd say that there is some leakage between the phase (hot) line and the metal screws. The power system basically has two wires. One (called neutral) is effectively grounded. When you touch the screws, the current goes from the hot line, through a leaky insulator or something to your fingers and then through your body to ground somehow, probably involving your feet and floor.

It's potentially quite dangerous. You should tell the landlord asap.

A circuit breaker is mostly there to stop your wiring and house going up in smoke in the case of an overload or short circuit. I don't think it's possible for enough current to go through your body to trip a circuit breaker. If it did then you probably wouldn't be here to tell the story. I'm talking about normal circuit breakers here, not those ground fault circuit interrupter things that are on bathroom and outside sockets. They detect exactly the current you're experiencing.
posted by tetranz at 9:52 AM on May 14

Yep this is an open neutral or bad ground or both. Possibly exasperated by a faulty single insulated appliance. Once you turn the breaker off you should see which other outlets are on the same circuit and verify that anything plugged into those outlets isn't shorted out.
posted by Mitheral at 11:32 AM on May 14

You could check the voltage on the screw with a multimeter measuring between the screw and an earth ground such as a water pipe. If it is approaching line voltage you have a very serious hot leak. Kill the power until you can rewire it or have an electrician do so. If it is more like 40 volts or so it looks more like a floating ground. This is also quite dangerous. You should have three wires, hot, neutral and ground. The ground should go back to the panel ground which is earth grounded. Neutral should be at essentially the same potential, which is zero volts compared to earth ground. This can rise in an improperly wired circuit. If the grounding is faulty and some tyro has tied the neutral to the ground screw at the box the box, and that screw screws into the box. This could put the box at some level above earth ground, quite a dangerous thing. In any event I will kill the circuit, if you have access, until this is fixed. Basically, since you are renting you should call your landlord and have them send over an electrician PDQ.
posted by caddis at 12:01 PM on May 14

NOTES:

0) I may be wrong. :-) Read and follow at your own risk. If a number of MeFites jump in with "He's wrong", it is far safer to believe them. Please.

1) If you are not in the United States, IGNORE THIS.

2) If the area you are working in isn't dry, or has metals near -- wet floor, metal rails, water pipes nearby, IGNORE THIS. This could KILL YOU if you took full current in one hand and a solid ground in the other.

3) If you don't feel confident that you understand after reading this, IGNORE THIS.

4) If there's no power, it can't hurt you. The safest breaker to throw is "all of them." Does make it hard to work, and is annoying. If you throw all the breakers, including the master, and the outlet tester still lights up, CALL THE ELECTRICIAN.

If you have a plug-in outlet tester, like this, you can figure out what's wrong. More importantly, you can test all the outlets and see if A) any more are badly wired or B) if the entire circuit is badly wired. If many outlets show the same fault, it is very likely to be a central wiring problem, and you need an electrician.

A) you can fix yourself if you are careful. Turn the power off. Test the outlet again -- if the tester lights up, then you didn't turn off the right breaker. If you can't find the right breaker, you're out your realm.

Once the power's off, remove the faceplate. The outlet should be held to the box by two screws, top and bottom. Remove those and pull the outlet, with wires, out.

Examine the wires attached to the outlet. There should be three -- a white or gray one, a bare-metal or Green (possibly with Yellow Stripe) one, and another one, which is often Black or Red, but might be some other color -- but not Green, Grey, or White. If you have two blacks, two reds, two whites -- anything not clearly a Color or Black, White/Grey, and Bare Wire/Green, replace the outlet, call the electrician -- it's either an older wiring spec, or it's completely screwed up and you don't want to mess with it.

The most common combination on stuff built in the last 25 years is White, Black and Bare wire.

Now, examine the outlet. It should have one or two silver screws on the (usually) left side of the outets, one or two brass screws on the (usually) right side of the outlet, and one (usually) silver screw somewhere else -- often at the bottom of a normally hung outlet. If this isn't clear, put the outlet back, call an electrician, or go buy one that is clear.

The White or Gray wire is the Neutral wire. It should be hooked up to the silver screw on the outlet. The bare wire is the Ground, it goes to the other screw. The other wire -- probably black, but it might be a color -- connects to the brass screw. Ensure that all three wires are tightly attached to the correct terminals. Replace outlet, reset breaker, test again.

If it fails the same way, you have one of two problems -- a bad outlet, or a miswired line. The former is *very* rare, but not impossible. However, the only safe way for you to test it to replace the outlet. If you do so, and the result is the same -- and wrong -- then you do three things. You flip the breaker, you call the electrician, and when he show up, you warn him that you think that the outlet may be wired wrong.

Notes:

1) You may not have screw terminals at all. In this case, you have stab-in terminals. These should be clearly labeled, and the white/grey wire goes to Neutral (or N), the bare wire to Ground (or G, or SG) and the other wire to Hot (rarely H, almost always spelled out.) Good stab-ins are very hard to remove the wire from, so replacement is easier. Some (more common nowadays) have both stab-in and screw terminals, in which case, you can pull or cut out of the stab-in and wire to the screw, if needed.

2) There are times in boxes where you will see two hots and no neutral, or two hots and a neutral, or two *different* hots and a neutral. Explaining all of this in a short AskMe answer is not a good idea. If you see more or less than One Hot, One Neutral, One Ground, close it up and call for help.

3) If there's more than one wire on a screw, it's wrong -- call an electrician (Besides, we're beyond the One Hot/One Neutral/One Ground rule here anyway.

4) If you die doing this, I'll cry for you, but it's your own fault!
posted by eriko at 12:21 PM on May 14

To keep it simple.. Does your apartment have all three prong outlets, all two prong outlets, or a mix?
posted by Chuckles at 6:54 PM on May 14