What can cause a house's lights to flash?

September 8, 2008 10:47 AM

What can cause a house's lights to dim and flash?

I just moved into a new house (in Noe Valley in San Francisco). The house lights flash periodically; about 4 flashes a second for a minute or so. It happens roughly once an hour. The power doesn't go entirely out, all the various electronic gizmos stay on. But the lights dim and brighten.

What can cause that? The house is 1930sish and San Francisco's power infrastructure is not great. It's circuit breakers, not fuses. We just did an extensive remodel and installed a lot of new appliances. As near as we can tell the lights don't flash when any specific appliance is operating, but we could have overlooked something.

posted by Nelson to home & garden (7 answers total)

Could be a loose neutral
If all the lights in the house flicker it could be the neutral at the main panel other wise its buried in a junction box somewhere
splices can come or burn apart after time
posted by SatansCabanaboy at 10:58 AM on September 8, 2008

Try and narrow it down more - is the refrigerator compressor kicking in? Did you have central air installed, and is that kicking in? I've even known a house where the pool filter wasn't on a dedicated circuit, and when it kicked on it drew enough current to freak everything else out for a few seconds.

Check out this link for a long (and only slightly confusing) discussion of this problem.
posted by pupdog at 11:06 AM on September 8, 2008

Definitely check the main and ground connections at your breaker box, and if you have more than one breaker box, check the connections between them.

I had this problem (flickering lights, lots of UPS turnons, brownouts) in a house built in 1971. The problem ended up being that the place originally had aluminum wiring. Everything had been replaced with copper, except for the single run between the "outside" breaker box and a sub-box in the garage that was still aluminum.

Electrician showed up, looked at it for ten seconds, tightened down the screw/clamp/termination point, and charged me $20. He also told me to check and tighten it if necessary every six months or so.
posted by mrbill at 11:14 AM on September 8, 2008

Seconding a loose neutral wire. My house gets this problem periodically, and it's because the wind (which is usually gusty and almost incessant in my neighborhood) works the wires a bit loose at the "periscope" (where the PG&E cables connect to the house). PG&E comes out and tightens them and the problem is solved for 6 - 12 months.

If your problems are worse on windy days, this might be the answer. In any event, describe the situation to PG&E and ask if they could check your power feed. I've found them to be very fast and helpful with stuff like this.
posted by Quietgal at 11:51 AM on September 8, 2008

When my printer is on, all the lights on that circuit flash/dim quite randomly, doesn't matter if it's just turned on or has been on an hour, printing or not.

Try to unplug all appliances that you can, and then plug them in one by one to see when the problem starts.
posted by Sonic_Molson at 12:05 PM on September 8, 2008

Once an hour, do you say? Perchance, do those lights have dimmers or touch switches on them?

Could be the control signals sent along the lines by the power company - high frequency tones used for switching things like off-peak hot water systems & swimming pool filters, telemetry, etc. In most countries I've heard of, this usually happens hourly (usually a few minutes before or after the hour - around here, there's minute or two long sequences of them at about 3mins past the hour), and mostly at night or around lunchtime. The control signals get into the gate circuit of the dimmer / touch switch, which bounces around in level and causes the lights to flicker.

The same problem can occur with cheap audio gear, where the control signals aren't filtered out by the power supply and can be heard quietly in the speakers.

The problem can be exacerbated by bad earthing, but quite often it happens anyway regardless of the quality of the earth. Better quality dimmers / touch switches are usually immune to a lesser or greater degree, and there are whole-house filters (installed at the meter box / lead in) which can help mediate the problem.
posted by Pinback at 8:24 PM on September 8, 2008

Thanks for the answers! Armed with a little knowledge from AskMe I talked to our electrician and he tightened a bunch of looseish wires at the breaker box. No flickering since, and if I get more flicker on a windy day I'm calling the power company.
posted by Nelson at 3:44 PM on September 9, 2008