Voltage Detector doesn't beep when light switch is on??

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Old 10-22-12, 10:49 AM
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Voltage Detector doesn't beep when light switch is on??

Does this raise any red flags to you?

Tool: a non-contact voltage detector...I've used it hundreds of times in other houses before, but I've never come across this...

Setup: POWER SOURCE === BULB === SWITCH (switch at end of circuit)

When tweeting the conductors between the BULB and the SWITCH (===),
  • Switch & light OFF: Voltage detected (BEEP BEEP)
  • Switch & light ON: Voltage not detected (silence!)

Maybe the wiring in the fixture is backwards, with the switch in the neutral? I haven't opened up any of the lights yet. Since all of them are like this, I'm hoping that this makes some sort of sense...
 
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Old 10-22-12, 01:18 PM
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If it is a spst switch you should have voltage on both legs when it is "on". If it is a 3 way switch, then only one traveler at a time will show voltage. You may want to get an analog vom ($20 at Lowe's) to help with more accurate measurements. Non contact testers will give false readings when you least expect it. Also, if you are using one, be sure to test it in a known good source (receptacle) before you go testing. If your battery is dead, it won't show voltage present, which can make for a non happy day.
 
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Old 10-22-12, 01:40 PM
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I tested near outlets and the n/c voltage tester is working great. Everything else is predictable except for these switches. It is a SPST switch.

[Breaker]
||
||
||
[Light]
||
|| <-- Holding N/C volt tester here
||
[spst]

Lights off: Tester shows voltage present
Lights on: Tester shows no sign of voltage on either leg.

This seems bizarre to me.
 
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Old 10-22-12, 02:42 PM
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And I have never wasted my money on a non-contact tester because they are all but worthless. Get a cheap analog multimeter. The fact you have used it three hundred times and guessed correctly only means you should play the lottery.

Is the light not working? At the switch disconnect the incoming power and test between the black and white with a meter or test light. (No need to test switch connections with a meter or test light.) Reconnect power. Open up the light and test for power with a meter or test light. To test switch remove the two wires connected to the switch and wire nut together.
 
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Old 10-22-12, 02:57 PM
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The lights do work. The switch seems fine.

I'm not trying to get the light to work...just trying to understand why on earth the n/c tester chirps only when the light is on.

I've seen plenty of false positives, and I'm OK with that.

So, faulty tester or not... this is a curiousity thing. What is it about the light switch that could make the tester NOT chirp when the lights are turned on? (but chirp when they're off)
 
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Old 10-22-12, 06:26 PM
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If I understand correctly, you have a switch loop that is probably connected incorrectly at the ceiling box. You probably are switching the neutral conductor instead of the hot conductor, thus no voltage is detected when the light is turned on. I've seen it many times.
 
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Old 10-22-12, 06:57 PM
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If you open the fixture you will see the line power in the box. The black of that should be tied to the white of the switch wire

whats happening I think is that the switch is interrupting the neutral instead of the hot
 
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Old 10-23-12, 06:27 AM
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Thanks CasualJoe and Jayhova. I'll open some fixtures and see if the line's hot or neutral is being switched.

I'm under the impression that for the sake of future debugging, testing, etc... the hot black should be switched. If it were your house & the switch was interrupting the neutral leg, would you take down the fixtures and redo it so the switch interrupts the hot? Would this be necessary in case a fixture is ever installed with a ground?

(typo fix from a previous post)
The lights do work. The switch seems fine.

I'm not trying to get the light to work...just trying to understand why on earth the n/c tester chirps only when the light is off.

I've seen plenty of false positives, and I'm OK with that.

So, faulty tester or not... this is a curiousity thing. What is it about the light switch that could make the tester NOT chirp when the lights are turned on? (but chirp when they're off)
 
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Old 10-23-12, 06:22 PM
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If it were your house & the switch was interrupting the neutral leg, would you take down the fixtures and redo it so the switch interrupts the hot?
Definitely YES! I think what you'll find when you remove the fixture is 2 white wires and 2 black wires. Normally all neutrals (whites) are spliced together, but not in this case because 1 white wire IS NOT A NEUTRAL. In this case the hot black wire should have been spliced to the white switch loop wire leaving in the ceiling box 1 white neutral and 1 switched black hot wire to connect to the fixture wires. What I believe you'll find is 2 white wires spliced together (as if they were both neutrals) and 2 black wires connected to the fixture wires. If this is the case, the fixture now has power going through the lamp filament all the time. Voltage now will be read at the switch till the switch is turned "On". Once the switch is "On" and fixture lights up, the wires at the switch are simply connecting the neutral side of the load to the circuit neutral. As it is, you have a shock hazard just in replacing a burned out lamp.

Try this, with the switch in "Off" position, check for voltage at the switch. Now, remove the bulb and check again for voltage at the switch.
 
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