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1volt detected at light fixture when switch off?

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1volt detected at light fixture when switch off? java97301 07-28-2006
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Posted by on July 28, 2006, 2:00 pm
Hi,

I was hoping someone could tell me why my contactless volt detector
detects voltage at my light fixture when the switch is off and my
multimeter tells me there is a 1volt different b/t white and black.
Should I be concerned?

I have a 15amp circuit that comes into the switch and is then passed
onto the fixture. The fixture is probably the 9th item on the circuit.

Thanks for any help or references on reading material to learn more!

MG


Posted by peter on July 28, 2006, 4:50 pm
> Hi,
>
> I was hoping someone could tell me why my contactless volt detector
> detects voltage at my light fixture when the switch is off and my
> multimeter tells me there is a 1volt different b/t white and black.
> Should I be concerned?
>
> I have a 15amp circuit that comes into the switch and is then passed
> onto the fixture. The fixture is probably the 9th item on the circuit.

The 1 volt you measured could be an induced voltage. If you put a load on it
(e.g. screw back light bulb), it would probably drop to zero. Use your
ingenuity to figure out how to put a load on it and measure the voltage at
the same time :)



Posted by Jim Yanik on July 28, 2006, 7:48 pm

>> Hi,
>>
>> I was hoping someone could tell me why my contactless volt detector
>> detects voltage at my light fixture when the switch is off and my
>> multimeter tells me there is a 1volt different b/t white and black.
>> Should I be concerned?
>>
>> I have a 15amp circuit that comes into the switch and is then passed
>> onto the fixture. The fixture is probably the 9th item on the
>> circuit.
>
> The 1 volt you measured could be an induced voltage. If you put a load
> on it (e.g. screw back light bulb), it would probably drop to zero.
> Use your ingenuity to figure out how to put a load on it and measure
> the voltage at the same time :)
>
>
>

It's called "AC coupling";the small capacitance of the switch itself is
coupling voltage to the lamp.(google "capacitive reactance")

--
Jim Yanik
jyanik
at
kua.net

Posted by Bob on July 28, 2006, 4:52 pm

> Hi,
>
> I was hoping someone could tell me why my contactless volt detector
> detects voltage at my light fixture when the switch is off and my
> multimeter tells me there is a 1volt different b/t white and black.
> Should I be concerned?

The voltmeter is a high impedence device. Voltage can be induced
in the wire by the electric field where it is near other wires, but very
little current will be available. The voltmeter doesn't draw much
current, so it will display small voltage readings.
Don't worry about it - especially if it's only 1 volt.

Bob



Posted by EXT on July 28, 2006, 5:07 pm
One volt, heck I can get that reading by holding the voltmeter one of the
voltmeter in each of my hands. That is one volt between my left and right
hand.


>
>> Hi,
>>
>> I was hoping someone could tell me why my contactless volt detector
>> detects voltage at my light fixture when the switch is off and my
>> multimeter tells me there is a 1volt different b/t white and black.
>> Should I be concerned?
>
> The voltmeter is a high impedence device. Voltage can be induced
> in the wire by the electric field where it is near other wires, but very
> little current will be available. The voltmeter doesn't draw much
> current, so it will display small voltage readings.
> Don't worry about it - especially if it's only 1 volt.
>
> Bob
>
>



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