Remaining low voltage in outlet after fuse is turned off

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  #1  
Old 09-17-13, 10:48 PM
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Post Remaining low voltage in outlet after fuse is turned off

Hi,

I recently changed the power outlets in the living room and while doing that found that one of the outlets still has around 14V when the fuse that controls it is turned off (the voltage at the outlet is good 120V when the fuse is on). I am using digital multimeter to measure the voltage. Since I didn't want to touch the wires, I turned off all fuses and the voltage at the outlet dropped to zero then. I am not sure if turning off only a single fuse would have been enough, but I was wondering what could be the cause for this remaining low voltage?

Thanks.
 
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Old 09-17-13, 11:22 PM
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Welcome to the forums.

A digital meter can be very sensitive and can read induced or stray voltages. If you had plugged a table light into that receptacle you probably would have measured 0 volts.

When we make measurements like that all the time we use voltage testers that have a load in them that eliminate those erroneous readings. An analog meter would basically work the same way.
 
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Old 09-18-13, 07:08 AM
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I turned off all fuses
Fuses cannot under normal circumstances be tured off, but must be removed. You either removed the fuses, unscrewed the fuses or you have circuit breakers and not fuses.
 
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Old 09-18-13, 10:58 PM
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Thanks for the answers. Yes - I meant circuit breakers, thanks for clarifying the terminology for me.

When I put a load (a lamp) the voltage does drop to 0. Probably I am not the first to ask this question, but what is the reason such stray or induced voltage to exist for one of the outlets but not for others? Is it acceptable/permissible according to electrical standards? And why such a steady 14V reading I get (is the stray or induced voltage steady in nature)?

Thanks,
Ivan
 
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Old 09-18-13, 11:07 PM
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Picture this..........two wires are parallel to each other. One is live and one is not. The live wire sets up a magnetic field as the power passes thru it. That magnetic field will impose a voltage on the dead wire. It's a VERY low current signal. Strong enough for a digital meter to read it.... but weak enough that an analog meter, or a lamp will dissipate it and not respond to it.
 
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Old 09-18-13, 11:14 PM
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Originally Posted by Ivan Genov
[...]what is the reason such stray or induced voltage to exist for one of the outlets but not for others?
Induced or "ghosted" voltage is produced by inductance between a powered and un-powered circuit... specifically, the two circuit's cables running (at least roughly)parallel to each other. Length of the inductance determines current, while cable proximity/alignment determines voltage.
The current is typically miliamperes, like a small static charge. Only in industrial/commercial situations where there might be cables running in conduit (for say 100ft) would you run into any kind of significant current, enough to give you a harmless tingle.

Two cables touching but 90 degrees from each other will produce no induced voltage.
Two cables exactly parallel for any length but too far apart will produce no induced voltage.

As you might guess, this inductance is a very stable condition as the wires are not moving.
 

Last edited by Nick D.; 09-18-13 at 11:29 PM.
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Old 09-25-13, 09:05 PM
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Thanks to all for answers!
 
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