Is this induced voltage? Any danger?


Old 09-24-05, 12:26 PM
Bill W.
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Is this induced voltage? Any danger?

I suspect this is a normal phenomena of induced voltage but it surprised me. I am installing a wall-switch controlled, overhead light in a closet. I brought the cable from the source into the ceiling j-box where I connected the hot blackconductor to the white conductor of a length of romex which ran to the wall switch with the black conductor then returning from the switch to the ceiling box to be connected to the new fixture along with the white conductor from the source cable. It seems pretty basic.

When I turned to breaker back on my voltage detector showed both sides of the switch leg energized with the switch off. My digital multitester shows about 61-62 volts at the ceiling box with the switch off and 121.8 with the switch in the on position. My analog multitester barely registers with the switch off but shows 120-121 volts with the switch on. Is this type of reading just a characteristic of digital meters?

If this is an example of voltage induction resulting from the proximity of the source cable and the switch leg entering the ceiling box together there is nothing to worry about, right? Is there a shock potential from the 61 volts that the digital meter shows at the ceiling box with the switch off?

Thanks for your time and expertise.
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Old 09-24-05, 01:06 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Yes, this is induced voltage. Ignore it. It is not a danger as there is no current behind it.
Old 09-24-05, 02:46 PM
Join Date: Jul 2002
Location: upstate NY
Posts: 152
This is another reason to have a "wiggy" as well as a digital multimeter. A solenoid style voltage tester would not have shown this voltage and given you a more comfortable feeling about this situation.
Old 09-24-05, 07:48 PM
Bill W.
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Thanks racraft and weebee for your help. If anyone is interested in more info on "phantom voltage" someone on another web forum provided this link
Old 09-24-05, 09:33 PM
Join Date: Nov 2004
Location: CA
Posts: 2,041
It is NOT induced voltage due to the proximity of lines. It IS due to ohms law and Kirchoff's circuit laws, and the very high internal resistance of a DVM compared to an analog meter.
Old 09-25-05, 06:24 AM
Join Date: Sep 2003
Location: Central New York State
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In laymen's terms the voltage is induced.
Old 09-26-05, 01:12 AM
Join Date: Oct 2004
Location: USA
Posts: 719
More on phantom voltage. look at this link.

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