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Old 06-05-2010, 09:57 PM   #1
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Got a Little Shock


I'm in the process of installing drywall in a utility room. As I began to work around one of the outlets, I touched the metal box and got a light shock. I called out an electrician and he found that two of the wires in one of the two ceiling fixtures were crossed. He corrected the wires and said that would fix the problem.

The next day, I resumed installing the drywall. While mudding the joints in the drywall I got a slight shock. I began testing with a voltmeter and found that if I test between the ground wire and the drywall near the socket, I get voltage readings of .1 to 4.0. I get these readings even though the circuit breaker is off. Any idea what's causing the problem?

Thanks!

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Old 06-05-2010, 10:36 PM   #2
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Got a Little Shock


Maybe a nail penetrated another wire in that wall? Have you tried switching off all the other breakers, and does the voltage remain?

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Old 06-06-2010, 09:55 AM   #3
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Got a Little Shock


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Originally Posted by J.Gregors View Post
between the ground wire and the drywall near the socket, I get voltage readings of .1 to 4.0. I get these readings even though the circuit breaker is off.
Getting voltage with the breaker off makes me think it is a phantom voltage, and therefore usually harmless because it cannot deliver more than a few mA of current.

To get a shock with only 0.1 vac your skin almost has to be wet.

If the metal box is connected to a ground wire I'd say the ground wire is disconnected at the panel.
You can check this by measuring between the hot [black] lead and the ground lead. If you don't get a solid 120vac with this measurement the ground is floating.

Loading down the meter with any incand. lamp while you measure should also provide a clue as to where this voltage is coming from.

Last edited by Yoyizit; 06-06-2010 at 10:21 AM.
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Old 06-06-2010, 11:23 AM   #4
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Got a Little Shock


You wasted your money on that electrician. What wires were crossed? Crossed wires due not cause shocks????? Bad or wrong connections are the correct term, and very unlikely the cause. Sounds like static electricity due to the construction and dust in the room. Very very dry.

I personally can pull a 3-4 inch arc getting out of my truck. And that hurts. Hurts bad.
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Old 06-06-2010, 11:46 AM   #5
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Got a Little Shock


Thanks for the replies...

This morning I pulled the outlet out of its box and connected one of the voltmeter leads between the ground wire and the other to a nearby window screen. With the main breaker to the entire house off, I get .3 volts.

I then turned all the individual breakers off and turned the main breaker back on. I turned each of the circuit breakers back on one at a time. The readings I got, with the meter still attached as above, varied from .3 to 9.5 volts. The highest readings being when the major appliances were turned on. I suspect my initial shock yesterday happened when maybe the a/c or water heater kicked on.

Yoyizit,

I tried what you suggested...With the meter attached between the hot and ground wires, and the lamp turned off I get a steady 123v. With the lamp turned on I get a steady 122.9v. Does this tell you anything?

Thanks again!
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Old 06-06-2010, 12:00 PM   #6
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Got a Little Shock


J.V.,

Thanks for the input, I was typing my previous reply while you were posting...

The "crossed wires" term was what he told my wife, I was not here when he did the repair. I think he was referring to the neutral and grounds being switched. I'm going to have him come back tomorrow to take another look and show him what I found.

I think it's more than static electricity. I can actually get a voltage reading by touching the drywall near the outlet with one volt meter lead and the "ear" on the outlet with the other.

The first shock happened as I was putting the drywall joint compound on. It is moist, as I'm sure you know, and was apparently a pretty good conductor (as I was 3-4 ft from the outlet). The shock was one of those that makes you arm ache!

I appreciate your suggestions though!
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Old 06-06-2010, 12:13 PM   #7
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Got a Little Shock


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Originally Posted by J.Gregors View Post
I tried what you suggested...With the meter attached between the hot and ground wires, and the lamp turned off I get a steady 123v. With the lamp turned on I get a steady 122.9v. Does this tell you anything?
Yeah, it's a good ground, if the lamp was wired across [shunting] the voltmeter leads.

That window screen reading was a stray, with the screen acting like an antenna. I think it would read zero if your meter was loaded down with the lamp.

Mostly this doesn't make much sense, which means we're assuming something that isn't true. Figuring out what that could be can be real work.
If it weren't for your 'real' shock I'd say your meter was bad. You are using a DVM, right? I doubt that an analog meter would pick up window screen voltage.

I'm wondering if drywall mud contains salts, so it makes your skin very conductive.

The current path was through both arms or from a hand down to your feet?

Last edited by Yoyizit; 06-06-2010 at 12:25 PM.
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Old 06-06-2010, 12:42 PM   #8
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Got a Little Shock


Yoyizit,

I just connected the voltmeter between the groundwire on the outlet and the window screen, with lamp plugged in...with the lamp on or off, I get 1.9 volts. (Dont' know if that's good or bad??)

The meter is a Cen-Tech digital.

I'm definitely not an electrician, but it seems odd to me that I'm getting a voltage reading on a ground wire.

I don't know about the mud containing salt, but I still get a voltage reading after it is dry.

As far as the path, I'm not sure. I just know it was enough to make my hand and arm tinlge and ache a bit. It also shocked my daughter who was helping me with the drywall mud.

Thanks!
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Old 06-07-2010, 11:37 AM   #9
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Got a Little Shock


Have you duplicated the shock more than one time? Your voltage readings are completely normal.
Crossing of neutral and ground wires could cause an issue as the neutral is a current carrying conductor (CCC). So, it is possible your electrician was correct. I should say he did correct a problem.
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Old 06-07-2010, 09:31 PM   #10
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Got a Little Shock


J.V.,

The problem, and the voltage readings on the ground wire, persist even after the electrician corrected the wiring at the light socket.

I've found that when the house was built, they used the plumbing system as the ground. The ground wire is clamped on the line going into the water heater (which is near the breaker box). I think the system needs a proper gound (i.e. a metal rod in the ground). Anyone agree?
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Old 06-08-2010, 11:46 AM   #11
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Got a Little Shock


If you live within a half hour of Rockville, MD, I'd like to lug my bagful of test equip. over and check this out myself. Gasoline is on you. . .
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Old 06-09-2010, 11:00 AM   #12
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Got a Little Shock


Quote:
Originally Posted by J.Gregors View Post
J.V.,

The problem, and the voltage readings on the ground wire, persist even after the electrician corrected the wiring at the light socket.

I've found that when the house was built, they used the plumbing system as the ground. The ground wire is clamped on the line going into the water heater (which is near the breaker box). I think the system needs a proper gound (i.e. a metal rod in the ground). Anyone agree?
Just to keep thinks separate....
You haven't proved that you have voltage on the ground. Digital meters have a high input impedance and therefore can detect and measure voltage without loading the "circuit." The screen is an antenna which is full of 60 cycle interference. To get a shock you need to have a difference in potential between two points and the power source has to have enough power to provide current flow (ohms law). Even if the earth ground for you panel isn't perfect, everything in the house is referenced to this imperfect point. At your main panel, the ground bus and the neutral bus are bonded together so the only way to measure voltage on the ground would be to find an external know good earth ground and connect your meter to it and the ground bus in your panel.
I'm assuming all your boxes are metal. Metal boxes and all metal parts connected to it need to be grounded. If you have an open ground and a hot wire is touching somewhere you could have a hot box and everything will work just fine.
Here is one thing to do at the faulty outlet. Turn off your main breaker. Visually check the wiring in the box to make sure the box is grounded and the outlet is also connected to this ground. Then measure resistance from the box to the wide slot in the outlet. Use the continuity function or the lowest ohm scale. You should have less than 1 ohm.
Here are some things to help you understand this.
Take a common 9volt battery and put one index finger on one button and the other index finger on the other button. No shock. Ohms law I=E/R
9V/300,000= .00003 amps 300K ohms is typical body resistance. You need about 5ma (.005amps) to get a tingle. The body doesn't detect voltage - it detects current flow.
Question... Is the floor in this utility room concrete?

I've read back through the comments you have made and copied this from one:
The first shock happened as I was putting the drywall joint compound on. It is moist, as I'm sure you know, and was apparently a pretty good conductor (as I was 3-4 ft from the outlet). The shock was one of those that makes you arm ache!

When this shock happened what were you touching? You had a taping knife in one hand but where was your other hand and what were you standing on? It says you were 3-4 feet from the outlet so why would the outlet come into play?

Last edited by a7ecorsair; 06-09-2010 at 12:06 PM.
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Old 06-09-2010, 11:37 AM   #13
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Got a Little Shock


Quote:
Originally Posted by J.Gregors View Post
J.V.,

The problem, and the voltage readings on the ground wire, persist even after the electrician corrected the wiring at the light socket.

I've found that when the house was built, they used the plumbing system as the ground. The ground wire is clamped on the line going into the water heater (which is near the breaker box). I think the system needs a proper gound (i.e. a metal rod in the ground). Anyone agree?
The plumbing system and the ground rods are required to be bonded to the service panel, main disconnect or meter depending on who installed the electrical system. This is required and not wrong. The wire from the plumbing system and the ground wire should terminate at one of the locations mentioned above. Your meter readings are completely normal. You are using a digital meter correct? I can read a couple volts across my two hands with a digital meter. If you want to know for sure use a solenoid tester.
The bonding system should be comprised of the water line (plumbing system) buried metal plumbing pipe for at minimum 10' and within 5' of entering the house. There should be either ground rods, equipotential grid or re-bar footer connection. If you have at least one of the latter with the plumbing pipe you are compliant and correct.

Have you duplicated this shock? Your electrician may have already corrected the issue. I for one. think you and Yoyisit are making a mountain out of a mole hill.
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Old 06-09-2010, 02:34 PM   #14
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Got a Little Shock


Quote:
Originally Posted by J. V. View Post
making a mountain out of a mole hill.
FWIW, discriminating between mountains and mole hills: build a 120v "shock meter" to help separate matters of opinion from matters of fact.

Parts list
3000 ohm 2W resistor
300 ohm 2W resistor
30 mA or slightly larger fuse
100 mA fuse
AC milliammeter with a 200 mA range

Resistors are available from Radio Shack or places like Hosfelt. com. Total parts cost is a few bucks.

It also can be used in some cases for tracing leakage currents that trip GFCIs or AFCIs.

Last edited by Yoyizit; 06-09-2010 at 07:11 PM.
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Old 06-09-2010, 10:13 PM   #15
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Got a Little Shock


First, let me say thanks for all of your input. As I said in one of my previous posts, I'm no electrician, but I would like to be able to talk with the electrician and maybe give him some suggestions from you guys to see if we can solve the problem (be it mountain or mole hill) .

To clarify things a bit, there are four outlets in the room. They were all metal boxes but the electrician changed two of them to plastic when he came out last week. He indicated that would help reduce the risk of shock.

a7ecorsair,

I had the plastic putty knife in my hand, but was touching the drywall mud with my finger as I was spreading it. I was barefoot and standing on the concrete floor when I was bit.

After being shocked, I noticed that the joint in the drywall, that I had just taped and mudded, was touching the "ear" on the outlet where it screws into the box. I deduced that the current was apparently traveling from the "ear" thru the mud and then thru me .


I checked again tonight, and there is definitely some significant voltage coming thru the ground wire. I currently have 3 of the outlets pulled out of the boxes and if you touch the "ears" that hold the outlet to the box, you will get stung. I've changed out several lights switches and plugs over the years and have never had this happen before. Keep in mind, this wil happen even if you turn off the breaker to the entire room.

I spoke with the electrician's boss today and told him of my problem. I also told him how the electrical system appears to be only grounded to the plumbing system. He said that was the way they were allowed to do it back when the house was built (early 80's). (I think the house is lacking one of the items J.V. mentioned - "There should be either ground rods, equipotential grid or re-bar footer connection.")

Anyway, they are going to come out tomorrow and check into it further.
I'll be sure and post what they find.

I may be wrong, but it sure seems like this is not normal.

Again, thanks for the advice and Yoyizit, thanks for the offer, but I'm in Georgia and with the price of gas...

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