Power with switch turned off Why??

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Old 11-29-11, 07:09 PM
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Power with switch turned off Why??

I was preparing to replace an overhead light and noted that I have 57V across neutral and hot wires when the light switch is turned off; 120 when on. I checked other switched outlets on separate circuits in the house and found the same situation. I stripped the panel of all circuits except for the one in question and I still have voltage. I thought I might have a ground somewhere backfeeding power. The only way to get to zero volts is to open the breaker for the circuit I am testing. Same thing for the other two I checked. Why why why? Do I have three separate problems or one common?
 
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Old 11-29-11, 07:15 PM
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Are you using a digital meter? If so, you are most likely seeing what is called ghost voltage.
 
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Old 11-29-11, 07:33 PM
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Originally Posted by belgarid View Post
Are you using a digital meter? If so, you are most likely seeing what is called ghost voltage.
Yes on the digital. This sparks a vague memory of something I once knew. How do I test using a simplified method and without special meters to make sure I am just seeing ghost voltage? I
 
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Old 11-29-11, 07:41 PM
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Do you have a two lead tester that is used to plug into outlets to check for voltage?

Another is with the power on, turn the light on. Then turn off the breaker that controls the circuit for the light. Without touching the position of the switch (on), check for voltage using the digital meter. This places a load on the line and you should now get a zero reading.

The other option is if there are any outlets on the same circuit is to plug in a lamp and turn it on. This also places a load on the circuit that will drain the ghost voltage.
 
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Old 11-29-11, 08:05 PM
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Originally Posted by belgarid View Post
Do you have a two lead tester that is used to plug into outlets to check for voltage?

Another is with the power on, turn the light on. Then turn off the breaker that controls the circuit for the light. Without touching the position of the switch (on), check for voltage using the digital meter. This places a load on the line and you should now get a zero reading.

The other option is if there are any outlets on the same circuit is to plug in a lamp and turn it on. This also places a load on the circuit that will drain the ghost voltage.
The light circuit has a few overhead and one outdoor light on separate switches. When I open this circuit at the breaker the voltage goes to zero. With the breaker closed I can turn on/off the other switches/lights for this circuit with no affect on the 50 volt meter reading. I am measuring across disconnected wires of the j box for the light I intend to replace. Should I connect a new light and measure across it? I have not completed much testing on the other identified circuits.
 
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Old 11-29-11, 08:12 PM
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If you get a reading of zero volts with the breaker open you should be safe. Leave the breaker open when replacing the light. You may also want to place a peace of tape across the breaker with a note to make sure no one turns the breaker back on.

When you are testing with the breaker closed (power to circuit) you can still be picking up ghost voltage that is generated in the lines after the switch with no load on those lines. If you connect the new light you should get a reading of zero as it will now place a load on the circuit and dissipate the ghost voltage.
 
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Old 11-30-11, 12:12 PM
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As great as digital meters are, nothing replaces a $3 neon tester.
 
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Old 11-30-11, 01:57 PM
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Or even a cheap analog. Of course my Daddy used two lamp holders in series mounted on a base. Half bright 120v, full bright 240v, though he would have probably said 110/220.
 
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Old 11-30-11, 03:48 PM
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Originally Posted by ray2047 View Post
Or even a cheap analog. Of course my Daddy used two lamp holders in series mounted on a base. Half bright 120v, full bright 240v, though he would have probably said 110/220.
Thank you all,
I went back today and hooked up a light and measured across it with the switch off... 0 volts. So if I dig out my old analog meter I wouldn't see the ghost voltage?
 
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Old 11-30-11, 03:52 PM
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So if I dig out my old analog meter I wouldn't see the ghost voltage?
I never say never but I'm reasonably sure you wouldn't.
 
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