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Old 08-05-2008, 06:31 PM   #1
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Metal fixture has a charge


Hi again,

Now that my front lights are working properly again I have noticed something else. If you touch a voltmeter to the steel of the fixture and then touch the other end of the voltmeter to something that is grounded you get about 110 V. Also if you touch the metal of the fixture you get a mild shock. I noticed this once when I was moving into the house last year but I forgot to have a look at it until now. Has anyone run into something like this before.

Thank you for your time,

William

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Old 08-05-2008, 06:39 PM   #2
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Metal fixture has a charge


If this voltage can light an incandescent bulb, it is capable of supplying possibly lethal current.

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Old 08-05-2008, 06:40 PM   #3
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Metal fixture has a charge


Sounds like a "hot" wire is touching your ungrounded fixture. Fix the bare wire or replace the fixture, then ground it properly.
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Old 08-05-2008, 06:48 PM   #4
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Metal fixture has a charge


You have energized metal due to a ground fault. Cause is almost always no equipment ground in the wiring with a bare hot touching the metal of the fixture or you have a equipment ground in the wiring and it is open somewhere and a hot wire is touching metal, this will cause all metal to come to line voltage between the open in the equipment ground and the fault.
This is a very real electrocution hazard to humans if you touch something that is low impedance back to the source. Even the shock you received likely was enough amperage to be fatal if the current gets in series with your heart.
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Old 08-05-2008, 09:48 PM   #5
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Metal fixture has a charge


The fixtures themselves are grounded, so we can eliminate the no ground scenario. I'll start looking for a hot wire touching metal then. Thanks everyone.
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Old 08-05-2008, 10:16 PM   #6
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Metal fixture has a charge


If the ground was proper there could not be a voltage on the metal of the fixture. There are two problems. The ground on the circuit is open somewhere and the hot wire is somehow shorting or leaking to the ground.
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Old 08-05-2008, 10:59 PM   #7
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Metal fixture has a charge


As Joed is saying the fact that the fixture is grounded does not mean it will not have voltage on its metal. If the equipment ground of the wiring supplying the fixture is open ie broken anywhere on the way back to the circuit breaker panel all metal before that open is energized.

Please study this diagram below and I think it will be come clear. If the effective fault path is intact so that fault current can get to the center tap of the dwellings utility transformer the breaker will trip and deenrgized any line fault to ground on a branch circuit. Open the effective fault path at any point and a breaker can not trip and any metal likely to become energized will come to line voltage.
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Metal fixture has a charge-bonding-diagram.jpg  

Last edited by Stubbie; 08-05-2008 at 11:58 PM.
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Old 08-05-2008, 11:13 PM   #8
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Metal fixture has a charge


Quote:
Originally Posted by Stubbie View Post
Even the shock you received likely was enough amperage to be fatal if the current gets in series with your heart.
Please pay close attention to this fact that Stubbie points out. Even though the shock may feel "light", it'll kill you if it goes through your heart, which could happen under the right circumstances. Definately good to use extreme caution when investigating this problem.
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Old 08-05-2008, 11:59 PM   #9
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Metal fixture has a charge


When dealing with live power its usually best practice to always keep your LEFT hand in your pocket so as to prevent a path to ground through your heart. Also, its a good idea to remove any jewelry from your hands as well; getting electrocuted on a ring won't feel so good and may be more difficult to break away from it.
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Old 08-06-2008, 06:19 AM   #10
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Metal fixture has a charge


When testing for electrocution with bare hands never touch anything with the inner side of your hand - The hand will close on the thing and you will not be able to release it

Touching with the back side of the fingers ensures that if you get shock your hand will move away and disconnect from the electricity source

But there are better and safer ways to determine presence of hot on metal. A tester screw driver is probably the best one



Note that when a ground wire is broken somewhere the hot from one device may lead other grounded devices to become hot :



By testing ground wires in near locations you may find the broken ground wire place
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Old 08-06-2008, 09:03 AM   #11
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Metal fixture has a charge


Hi Ash,

So If I understand your diagram, the smaller hole in a receptacle is supposed to be the neutral wire?
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Old 08-06-2008, 10:14 AM   #12
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Metal fixture has a charge


wsixsmith No, the smaller hole is the hot side. Clockwise from the top; Hot, ground/earth, Neutral. That type of receptacle is for a grounded, polarized plug. On a polarized plug, the neutral blade is wider (taller) than the hot side. pete
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Old 08-06-2008, 10:49 AM   #13
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Metal fixture has a charge


My drawing is intended to show what becomes hot. They are the metal parts of the light fixture and the socket and the sockets ground hole

If you pug anything into the socket it will get energized too through the ground wire

The shorter slot in the socket is hot cause it is meant to be hot
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Old 08-06-2008, 12:23 PM   #14
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Metal fixture has a charge


Pretty soon you guys will be posting videos on this stuff!

And I guess with YouTube, it's possible. . .

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