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Old 10-07-2010, 02:07 AM   #1
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Post Stumped! Continuity but no voltage.

Any help would be appreciated... Today I had a customer who's stairway night lights were out (120 volt). I checked the photo sensor outside and it was fine. The photo sensor feeds two lights over the garage doorway before the line runs into the house and to the stairs.

I put a tone generator on the line at the stairs (black only) and got a strong signal at the photo sensor. Same for the neutral.

I bypassed the photo sensor and the garage lights work fine, but still no stair lights. I get about 2 volts at the stairs. Turned off the breaker and voltage dropped to 0.

I'm stumped. Any ideas? Anyone? Thanks!

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Old 10-07-2010, 02:10 AM   #2
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Originally Posted by hometodos View Post
Any help would be appreciated... Today I had a customer who's stairway night lights were out (120 volt). I checked the photo sensor outside and it was fine. The photo sensor feeds two lights over the garage doorway before the line runs into the house and to the stairs.

I put a tone generator on the line at the stairs (black only) and got a strong signal at the photo sensor. Same for the neutral.

I bypassed the photo sensor and the garage lights work fine, but still no stair lights. I get about 2 volts at the stairs. Turned off the breaker and voltage dropped to 0.

I'm stumped. Any ideas? Anyone? Thanks!
2 volts from what to what? Ungrounded to grounded, ungrounded to grounding?

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Old 10-07-2010, 02:22 AM   #3
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I'm stumped. Any ideas? Anyone? Thanks!
Did you physically open up the 2nd garage light and check out the connection feeding in to the stairs?

A toner has it's place but I prefer physically checking splices if part of a circuit is mysteriously not working after a certain point.
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Old 10-07-2010, 02:24 AM   #4
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really, silly question, but sometimes it's the right one.....did you check the light bulb itself? Or flip the breaker? Or that gfi hidden in the garage for some weird reason?
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Old 10-07-2010, 02:27 AM   #5
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Time to call an electrician.
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Old 10-07-2010, 02:53 AM   #6
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Yes, erics37, I checked both lights over the garage and the wiring is fine.

Answer to BCSparkyGirl: My tests at the stairs were on the line feeding it, with the chain of lights diconnected. (they all work fine with another power source). No GFCI on this circuit. Breaker not tripped.

Answer to Jlarson: 2 volts AC black/white wires
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Old 10-07-2010, 03:19 AM   #7
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Your initial assumptions as completely incorrect. You state, "continuity but no voltage", yet you checked continuity with a toner? Give me a break. Get out an extension cord or roll of THHN and check with a meter. Something's broke somewhere.
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Old 10-07-2010, 03:31 AM   #8
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Ok MDShunk. I'll do that. thanks.
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Old 10-07-2010, 03:33 AM   #9
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Answer to Jlarson: 2 volts AC black/white wires
Did ya check from hot to ground?

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You state, "continuity but no voltage", yet you checked continuity with a toner? Give me a break.
Yeah, not my first choice either.
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Old 10-07-2010, 06:05 AM   #10
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Time to call an electrician.
gonna have to go with 480 on this one....

a toner???????
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Old 10-07-2010, 07:16 AM   #11
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Tone generators can actually be wonderful troubleshooting tools in some situations! They work perfectly with romex. I've had mine lead me to tripped GFI receptacles in 2 different basements. In both cases, the homeowner had no idea that those receptacles even existed. One was in a linen closet behind some towels and another in an unfinished area behind a bunch of boxes!
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Old 10-07-2010, 07:19 AM   #12
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broken wire, or bad splice.
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Old 10-07-2010, 02:26 PM   #13
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Originally Posted by hometodos View Post
Any help would be appreciated... Today I had a customer who's stairway night lights were out (120 volt). I checked the photo sensor outside and it was fine. The photo sensor feeds two lights over the garage doorway before the line runs into the house and to the stairs.

I put a tone generator on the line at the stairs (black only) and got a strong signal at the photo sensor. Same for the neutral.

I bypassed the photo sensor and the garage lights work fine, but still no stair lights. I get about 2 volts at the stairs. Turned off the breaker and voltage dropped to 0.

I'm stumped. Any ideas? Anyone? Thanks!
Begin by switching to low impedance or a solenoid meter. Then once you discover you have 0 volts, switch to continuity and find the break
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Old 10-08-2010, 01:04 AM   #14
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Originally Posted by MDShunk View Post
Your initial assumptions as completely incorrect. You state, "continuity but no voltage", yet you checked continuity with a toner? Give me a break. Get out an extension cord or roll of THHN and check with a meter. Something's broke somewhere.
Toners only work on normally open wires, short them together and the tone stops.

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