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Old 09-24-2005, 07:50 PM
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Bill W.
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 09-24-2005, 08:21 PM
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Yes it is, only with digitals will you see it. It's called Phantom Voltage. Here's a link that'll explain it in detail.

http://repairfaq.ece.drexel.edu/REPA...ml#APPFAQJ_019

It's not dangerous, no worries there.
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Old 09-24-2005, 09:44 PM
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Bill W.
Thanks for the information and the link. I really appreciate it.
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Old 09-25-2005, 07:36 AM
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Digitals are highly sensitive. Analog meters inputs feed through several range resistors before the actual meter. Digitals have amplifier circuits, range resistors and a 555 up/down counter circuit so it will pick up anything.
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