What's causing my lights to pulse?

March 11, 2005 8:57 PM

The lights in my house occasionally pulse--that is, they'll rapidly get noticeably dimmer and brighter numerous times within a matter of just a few seconds. I'd say "flicker," but they never seem to actually go completely dark. Does this indicate faulty wiring, or something else?

I live in an old (circa 1920s, possibly older) house in east Tennessee. The wiring coming up from the basement is, I believe, relatively recent vintage (1960s+). The overhead lights, though, are knob and tube wiring. They do the most pulsing, but even some floor lamps will do it. It doesn't seem tied to any major appliance's kicking into high gear (say, the air conditioner turning on or the dryer running). In fact, I've never been able to correlate it to anything, except one time where the lights in the bathroom pulsed in sync to the static I was hearing on my cordless phone. Any ideas? (I've tried googling for this several times but never came up with the right keywords to find relevant info.)

posted by kimota to home & garden (11 answers total)

An easy step, I guess, would be to ask your neighbors if they experience the same thing.
posted by TheOnlyCoolTim at 9:47 PM on March 11, 2005

Also, you may want to find out if anyone died in, or was buried under, your house.


Seriously, can you have someone install a line noise meter at your box to see if it's coming from the grid or originates inside your house?

You may want to pay attention to the wind as well- I've had a similar effect with a loose outdoor phone wire. It only would generate static when the wind blew in a certain direction.
posted by Four Flavors at 10:28 PM on March 11, 2005

a variant on a Brownout? Perhaps the local power company is experiencing high load?

Try this page, it may have your symptoms.

And.. if you don't have a good surge protector for yer computer, get one.
posted by edgeways at 10:59 PM on March 11, 2005

Do you own a laser printer? Those do some interesting things to the load on your AC.

If you're out in the country, it may just be farmers starting up heavy machinery. I noticed at certain times of the day I'd get brownouts for a while out in the country. Since only so much juice is going to your grid, if there's heavy users at certain times of the day it could affect you.

If it becomes a problem, a complaint to the local power company should get it fixed. :)
posted by shepd at 11:17 PM on March 11, 2005

This is almost impossible to diagnose from afar. The cause could be outside your house, due to wiring attenuated by age or storm damage, or electrical supply outstripped by an increase in demand. It could be bad or incorrect wiring at the breaker and your connection to the grid. I think it's most likely that your house's wiring just wasn't designed for the modern appliance-heavy home. The breaker might be a 100-amp panel when 200-amps is more common in new construction today. You don't necessarily need a new panel; you can add capacity with a subpanel. The real problem is subdividing existing circuits, as you can imagine. You can simply make sure that big appliances like dryer, fridge, AC are on their own circuits, for starters. An electrician can help you evaluate the amp load on various circuits, especially home office, kitchen, and workshop.

See Ten Common Wiring Problems and Installing a Circuit Breaker for an idea of the types of issues involved (and note that most municipalities require permits for anything more complicated than replacing a receptacle).

Meanwhile, make sure you have a top-quality power filter such as an APC or Tripp-Lite for any computer equipment. Brownouts themselves aren't necessarily harmful, but the surges back can be.
posted by dhartung at 11:55 PM on March 11, 2005

Working for a power company, I run into this problem quite often. I am guessing that since you have an older house then 99% of the time it is because of faulty connections regarding your overhead service. Call your electricity provider and tell them your problem. A lineman will attend and check your connections for free.

To make a short story: Your overhead connections have probably loosened over time. Not a big problem to fix.
posted by Kilovolt at 1:01 AM on March 12, 2005

Do the "flickers" happen at any particular time of the day (or night)?
posted by Jimbob at 2:54 AM on March 12, 2005

Thanks for the tips, everyone! It's going to take me a while to check out all my new leads!

A little feedback: I mentioned the shimmering to the guy who inspected the house, and he initially looked at me like I was crazy. I was able to point it out to him, but he had never seen it before (I'd seen it in an old apartment complex I'd lived in previously and others have seen it too, so assuming I'm not related to Scatman Crothers or Groundskeeper Willie, I'm thinking it's a purely natural phenomenon). I don't live out in the country (I'm in a traditional grid-style neighborhood), and I don't have a laser printer. I'm not too far away from some light industry type businesses, so that could possibly be involved. And the flickering seems to happen any time of the day or night, although I probably notice it more at night since I'm more likely to be using the lights at that time, of course. The wind idea is interesting; I hadn't thought to take that into account, and we have had problems with humidity affecting an improperly sealed component on the telephone pole that made the phone go out. I've got my computer equipment on surge suppressors, but not my TV (18 months and no problems yet).

Thanks again, everyone!
posted by kimota at 10:27 AM on March 12, 2005

I live in a 1920s apartment bbuilding adn we experienced this for years, worsening over time.

It turned out that a grease-like insulation had evaporated from exposed wire where the mains split to our individual apartment's power meter box. There were giant scorch marks where the arcing had charred the paint inside the box. Since the events went on for over a year and worsened over time, I beleive we were quite lucky that a fire did not result.

Get an inspection, pronto, and make sure the interior wiring joins are inspected. If you can isolate it to just a part of the house, find out where the junction is and take a good look at it.

BTW, the wiring was vintage 1980-something, so the 1920s thing was kind of a buffalo - originally I suspected the woven insulation rotting off the wiring in the walls.
posted by mwhybark at 11:56 PM on March 12, 2005

Happens to me too - sometimes the lights will just dim down & then come back up. Welcome to East TN kimota (I live in Farragut - we're on LCUB, assume you're on KUB) -- I've never been anywhere where I've had so much equipment blow due to line variations - talk to the power co. & they'll blame it on the squirrels. Go figure.
posted by Pressed Rat at 1:10 PM on March 13, 2005

Check out this thread. I had what sounds like the same problem in a house built in the teens. I took the light switch on the wall apart to get a better look at it and you know what I found out? It was one of those Radio Shack "control your lights from a remote control or home computer" switches. As far as I know, there aren't any other ones like it in the house, and the previous owners didn't use anything like that. I changed the "frequency" setting or something like that and the problem immediately stopped. I figured maybe one of my new neighbors bought one of these systems and was using the same frequency that mine was set to...
posted by pwb503 at 3:32 PM on March 13, 2005