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Last weekend, my kitchen ceiling fixture stopped working. It's a fluorescent fixture, and since the house is about 20 years old, I figured that ballast had gone bad. I went to the nearest home improvement store, grabbed a new one, and installed it.

No light.

As I mentioned, the house is 20 years old, and I've had to replace the occasional light switch and receptacle, so I thought that perhaps one of the two switches that control the light had gone bad. So I replaced them.

Still no light.

I next remembered that sometimes my GFCI would trip and cause issues on non-GFCI circuits. I made sure the GFCI outlets were working, reset it just in case.

Still no lights.

I've now pulled the new fixture out, and using a multitester, see I have essentially no current.

What could the problem be?

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Either the breaker has failed or there's a bad connection somewhere along the line. Check for voltage at the breaker and in each box along the line, the last box with voltage has a bad connection, probably one those push in connectors. –  bcworkz Apr 27 '13 at 18:29
    
I checked for voltage and found that there is no current going to the light switch. It's odd because the kitchen overhead light is on the same circuit as the front porch lights. The front porch lights work fine, and turn on and off when I throw the breaker. Doesn't that mean that the breaker is fine? I'm kind of at the end of my knowledge about wiring. When something is wired from a breaker, does it go to point A (porch) point B (kitchen ceiling) then back to the breaker? If so, how do discover each of the places the wiring goes? –  ScottC Apr 28 '13 at 17:04
    
I think I've mapped out the circuit. It feeds 4 light fixtures, 5 outlets, and 3 light switches. Would the last thing in the series be the one whose output is causing the problem? –  ScottC Apr 28 '13 at 18:04
    
Looks like we cross posted, your last question came up when I was typing the main answer. It's not the last in the series, but the last one that has power. There should be a connection there that leads to the kitchen wiring which is not working. –  bcworkz Apr 28 '13 at 18:14
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1 Answer

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I didn't have enough time yesterday to type up a proper answer, but I wanted you to have at least some information. For completeness, first my initial response.

Either the breaker has failed or there's a bad connection somewhere along the line. Check for voltage at the breaker and in each box along the line, the last box with voltage has a bad connection, probably one those push in connectors.

Based on your response, it sounds like the problem could be in one of the porch light connections where the power should continue on to the kitchen lighting. Which leads into your point to point question.

The wiring does loop back to the breaker, but not in the way you think, unless you have war time British ring wiring. Other than ring wiring, all conventional wiring is either linear or tree organized with pairs of wires (plus ground hopefully) making each run between boxes. Current runs up one wire, usually black in the US and brown elsewhere, and back along the neutral, usually white in US and blue elsewhere. In other words, the out and back is achieved in the same cable with a wire pair, not by separate cables. Assuming conventional non-metallic (romex) cabling.

Actually, alternating current doesn't go anywhere, it vibrates back and forth, but the direct current model serves conceptually to ensure power and neutral connections are properly maintained. Since circuit layouts can be almost anything, without a wiring diagram, only methodical checking of various wires in each box will reveal the actual layout. It's usually a safe assumption that the layout is roughly efficient in wire use, you're unlikely to see runs double back on itself without good reason.

Since the porch lights work on the same breaker and are fine, yes the breaker itself can be eliminated as a problem. It is possible the power connection that has failed is located in the breaker panel though, as two separate lines out of the same breaker could be possible, though somewhat unusual.

With that background, you should try to locate where the power runs from the porch lights to the kitchen lights. It may be from the switch or the light, or it may be a branch farther back towards the breaker. There may also be another box for something else between the porch and kitchen lights. You will need to guess at the probable layout to have any hope of locating the bad connection without testing the entire circuit. Wires typically run from closest box to closest box. Don't forget switches in two different rooms can be only inches apart for wiring, the boxes only happen to open into different rooms.

Also verify the power comes from elsewhere to the switch and not to the light. If there are only two wires, one cable at the switch, the power is coming through the light first, where you will find at least two cables and four wires. Unfortunately, there are also layouts involving three wire (plus ground) cables where where the power comes from is ambiguous.

A lot of talk for all you really are trying to do is find the other end of the wire which should have voltage but doesn't. Unfortunately, finding it is either a lucky guess or being thorough and methodical. I wish I could help more, but I can't be there to help you, but I am here fairly regularly if not frequently if you have any more questions. Good luck.

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Thank you!!! I thought about what you said and the most logical next thing in the sequence was the light switch in the dining room, which was working to turn on the dining room light, but when I checked it with the multimeter, no current was leaving it. I replaced it and the kitchen light now has power! –  ScottC Apr 28 '13 at 19:31
    
Awesome! I love it when logical deduction works. Without it, locating this sort of fault can involve a lot of testing, and usually a lot of confusion. –  bcworkz Apr 29 '13 at 15:38
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