Less than 120V? Newbie questions..


Old 05-21-05, 10:08 AM
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Less than 120V? Newbie questions..

I have 2 switches that I'm trying to troubleshoot. Neither of them work anymore. I tested the first line with a digital multimeter at the switch terminals and it was showing 50V. I thought that maybe I had a bad switch, so I cut power, removed the switch, and tested the wires at the box again... 50V yet again. Next, I removed the lighting fixture, capped the hot and neutral lines at the fixture end and tested again at the switch box... 120V. So, I'm assuming I have a bad fixture. Is this correct?

The second line in question is hooked up to a hallway light run by 2 3-way switches. Readings from both of the switches terminals shows 11V. What's the deal with this? Could it just be a bad 3-way switch? I haven't done any further troubleshooting with this one yet, aside from testing for voltage at the fixture which I believe didn't show any voltage.

Note: Bear in mind that while I've been working with DC (mobile audio, etc.) for many years, I'm pretty new to working around the house with AC so I'm a newbie. Be gentle.
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Old 05-21-05, 05:37 PM
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Update: Looks like I was right about the first line. Put up a new fixture and it's working fine again. The second one is still giving me problems, though. Replaced both 3-ways AND the fixture and nothing. Still showing very low voltage at either 3-way. I guess I have a break or bad fixture somewhere else in the line?
Old 05-21-05, 06:06 PM
Join Date: Sep 2003
Location: Central New York State
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Put away your digital multimeter and do not use it for AC testing. You are reading phantom voltage. Use either an analog multimeter for ac testing or use a simple neon light tester.

While switches do go bad, it is usually easy to tell because they don't feel the same anymore when you use them. Most problems are due to a failed connection.
Old 05-22-05, 07:13 AM
Join Date: Nov 2004
Location: CA
Posts: 2,041
The phantom voltage referred to means that you are measuring across an open in the circuit, or the high internal impedance of the meter is able to develop a reading from other stray sources. I use a digital MM all the time, but you have to understand what it is doing.

The chance that some point in your electrical system would actually have 50 or 60 volts, vs 120, is really nil. You just put Ohm's and Kirchoff's laws into effect and see what is going on in the circuit.

To reiterate, your 50 volt reading is probably across an open in the circuit.
Old 05-23-05, 04:55 PM
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Sometimes ( with digital meters ) the effect can really throw you off unless you are used to seeing it. Most electricians at some point have figured this out but in the event of the (2) 3-way switches....

On that same Digital meter you probably have a Continuiety tester feature as well....cut the power and using the 3 wires you have to each switch...you would ring it back to find which are the travelers and which is the hot and feed to the light....just another way to do it as well.....

Man I think I spelled Continuiety wrong....man I need spell check on my posts.....

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