Weird Wiring Issue -- Flickering Lights

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Old 02-23-10, 06:34 AM
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Weird Wiring Issue -- Flickering Lights

Hi,

I have a very peculiar lighting issue in my bathroom where the lights sometimes flicker rapidly and randomly, while other times they remain steady and normal. Still other times they fail to turn on at all. Last evening I discovered that the bathroom lights would always remain steady if I turned on the overhead light in the adjoining bedroom. This morning I tested it by using a table lamp plugged into an outlet in the adjoining bedroom and that also kept the bathroom lights steady. In all of this, the lights in the adjoining bedroom initially flicker once, if at all, and then are constant, regardless of whether the bathroom lights are on or not. As soon as I turn off a light in the adjoining bedroom, the lights in the bathroom begin to flicker very soon after and then eventually go out altogether.

This suggests to me that the bathroom junction box is wired in series through the adjoining bedroom junction box. But the puzzle is that oftentimes the bathroom lights will work just fine regardless of whether lights in the adjoining room are on or not. I have not been able to decipher any pattern as to when they will work or not. I just know that when they don't work, I can get them to work by running power through the junction box in the adjoining room.

I've looked at the connections at the breaker panel and in the bathroom and didn't see anything amiss. I went in the attic the other day, but I haven't found everything up there yet. It's hard to safely move around up there because the insulation obscures the joists.

Here are all the items on the breaker:
Bathroom - Two wall sconce light fixtures, a GFI outlet, an overhead light fixture, and two wall switches (1 for wall lights, 1 for overhead light).
Adjoining Bedroom - An overhead light, three outlets, and a wall switch for the overhead light.
Random - There's also a run that comes off the junction box for the bathroom that runs to an outlet in a room that butts against the other side of the bathroom.

The house is approximately 100 years old, but it appears to have modern copper wiring in the attic where the trouble seems to be. The wiring runs straight down to the cellar via an old gas line that was originally used for gas lights in the house, so it seems it should be pretty well-protected. I have not seen any signs of rodents or other pests anywhere in our house. We have a 100-amp panel. The breaker is either 15 or 20 amps (I can't recall at the moment).

My electrical knowledge background is very minimal so please ask for clarification if I'm not using the correct terminology or not being clear.

Thanks in advance to anyone who can help.
 
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Old 02-23-10, 08:56 AM
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Originally Posted by nrz13 View Post
I have a very peculiar lighting issue in my bathroom where the lights sometimes flicker rapidly and randomly
Flickering lights is almost always caused by a loose connection, or a bad switch (which is really a special case of loose connection).

The fix is a little tedious, but effective. Open up each junction box including light fixtures, switches and receptacles on the circuit. Check all connections for tightness and remake if they are loose. Replace the switches (at $0.49 why not?), and move any backstabbed wires to the adjacent screw terminals. A backstab is when the wire is inserted into a hole in the back of the switch or receptacle instead of wrapped around the screw. The spring inside that hole weakens over time. When you have the light fixture boxes opened up, inspect the wiring for heat damage such as burnt or cracked insulation. Overlamped fixtures can cause wire insulation failure which also might cause flickering.
 
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Old 02-23-10, 08:58 AM
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You need to open all boxes, lights, and receptacles on the circuit and tighten any screws, and replace any wires nuts. If there are any Jboxes related to the circuit in the attic they need to be opened and the wire nuts replaced.

You can test wire nuts by just tugging on the wires going in but occasionally the wires may seem secure when they aren't or the wire nut may have corrosion inside.

Edit: OOps ibpooks beat me by 2 minutes and included the backstabs I left out. They are very important.
 
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Old 02-24-10, 08:13 AM
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Thanks ibpooks and ray2047. My Dad and I have done some of that, but we'll keep hunting for it and try your other suggestions. Finding the problem is the hardest part.

It wasn't so much the flickering lights that struck me as weird, as I assumed it was a bad connection somewhere. It was the fact that switching on another light elsewhere on the circuit stabilized the flickering in the bathroom (and do keep in mind that it isn't always like this -- sometimes the lights work just fine without anything else on the circuit being on). Any ideas on how that could happen?
 
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Old 02-24-10, 08:27 AM
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Originally Posted by nrz13 View Post
Any ideas on how that could happen?
It's a little bit of a stretch, but the temperature of the wires can affect the quality of the connection. Turning on the other lights could cause the splices to heat up enough and expand to make a good-enough connection.

It's also possible given the age of the house that there could be some interconnection of circuits or funky cable routing whereby switching on the neighboring lights backfeeds the flickering circuit.
 
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Old 02-24-10, 11:07 AM
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Originally Posted by ibpooks View Post
It's a little bit of a stretch, but the temperature of the wires can affect the quality of the connection. Turning on the other lights could cause the splices to heat up enough and expand to make a good-enough connection.
Yeah, I could see that being the case. It's been cold here lately, so the wires could really be depending on that heated wire to expand enough to complete their connection. I don't think this problem started until the weather got cooler so I think your guess has a lot of merit. Thanks for the input!
 
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Old 02-24-10, 11:23 AM
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If the problem is weather related you also might want to look for a junction box where condensation might be forming. Warm air from inside leaking into a cold junction box can cause water droplets to form. You can use a candle flame to see if there's a draft coming in through the switch or receptacle boxes. You can get gaskets that go under the coverplates to better seal the box or insert the tube behind the junction box and shoot some Great Stuff foam behind and around the boxes, especially if they are in an exterior wall.
 
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Old 02-24-10, 12:18 PM
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Noted -- thanks!
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