Switch Testing


Old 09-04-05, 10:22 AM
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Switch Testing

Hello, I'm currently wiring my unfinished basement and have started testing my work before putting up drywall. When measuring the voltage for my 3-way switches, I'm getting 120V (on) and 60V (off). This is the case for 2 different pairs of 3-way switches now. The lights work fine - if I wasn't measuring the voltage @ the switch, I wouldn't suspect a problem. Have I done something wrong?

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Old 09-04-05, 12:13 PM
Join Date: Nov 2004
Location: CA
Posts: 2,041
You have to draw the electrical circuit and realize exactly where in the circuit you place the meter. A meter placed across and open completes the circuit thru its internal resistance. Current flows, and some voltage is dropped across the load ( the bulb). The current is too low to cause the bulb to glow, but it will cause the meter to read volts. Digital MM with hi Z-in are especially prone to this so-called phantom voltage. Just as sure as the law of gravity applies if you drop your meter, Ohm's Law will always prevail in a circuit.
Old 09-04-05, 03:20 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Digital multimeters are of extremely limited usefulness in testing home wiring. If you want to test your wiring, it is much, much better to buy a simple $3 porcelain light fixture and connect it at where you will put the light, or temporarily install the receptacles and use a plug-in lamp. In fact, if you're unsure of your wiring, then temporarily connect all light fixtures, switches and receptacles and conduct a full operational test. Of course you'll have to remove them all before the inspection and drywalling, but it'll give much clearer results than your meter.
Old 09-05-05, 02:47 PM
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Switch Testing

Thanks a lot for your input - I've wired in switches, recepticals, & fixtures like you suggested and everything looks good!

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