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Quick light flicker question

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John Connor

John Connor

Lifer
So for years I have noticed especially when I'm on the patio that the hanging lights we have will go off then on in like a quarter of a second. It's like an electrical hiccup as best as I can describe it. I have seen this phenomena in the house as well with a ceiling light flickering off then on in a fraction of a second.

So what is the cause to this? Is it a power transfer or something at the plant? Is this what's called a power sag? Or is that something else all together? I know it's nothing in the house. Any big appliances we have are a fridge and deep freezer in the garage and when I'm out there and they go on I don't see the light flicker.
 
If something on the same transformer pulls a huge amount of power (such as an AC unit starting) it will cause a temporary voltage drop due to the high amount of amps being pulled. This is basically what causes a flicker.

In some cases it could be a power transfer but usually those will be more like a very fast power outage that lasts maybe 1-2 seconds. I see it some times at work monitoring various buildings, we'll see a bunch of power outage alarms for a bunch of buildings in a general location, then they all clear. Typically when a truck hits a pole or something. I think the power companies has various transfer stations where if one source is cut it will switch a grid over to another source. Guessing it's all automated, almost like a UPS switching to battery.

Could also be loose wiring somewhere and with the wind it creates a point of high resistance and voltage drops when the wire is in a certain position.
 
It could be the guy a few house down behind us. He has a welding biz by the looks of it. But this flicker happens at like 2AM as well. No wind.
 
completely off then back on?

are these LEDs?

The closest to this I've had was when I believed the listing agent on my late 1800s apartment. He said that all the wiring was new. Turns out that I shouldn't have plugged my portable air conditioner into the old-ass wiring. The wiring ended up overheating, expanding, then temporarily losing connection from up the line. Happened a few times, then I was completely disconnected.

Same rental agent told me I could get a street parking permit from the city. That was a lie, too. Wonder if he's still employed.
 
Not completely off. It's a brief flick of the light like if you turned the light off and on really quick. I guess that means completely off, doesn't it? LOL But it doesn't look like it goes completely off though. That's how fast it is.
 
Voltage dips are fairly common. There can be many causes.

Local causes include motors (which take a big current surge at switch on) for water pumps, elevators, HVAC, etc. My brother lives in a small apartment block (about 20 apartments on 3 levels) but it has a water pump in the basement to boost mains pressure for the top floor. Every time the pump starts, the lights flicker for an instant as the voltage drops.

More distant causes can be very high power equipment or faults which cause a voltage dip on the high voltage lines to your transformer. Examples could be industrial spot welding equipment. In this case, although the spot welder was 400V, it was taking such big current surges that it was causing the 11 kV supply to the transformer to sag, and everyone else whose power came from the same 11 kV feeder was having their lights dim.

Faults can also cause voltage dips - if someone on the same transformer shorts out their power supply, then it can cause a serious voltage sag on the transformer (until their fuse blows), and if the transformer is big (like in industrial areas) then it can also cause a serious dip on the feeder.

Feeder faults can also cause a similar effect. If a feeder shorts out, then it will likely place a serious sag at the main substation where it gets its feed, and that sag may go back through the substation transformer into the extra high voltage lines, until a circuit breaker trips out.

In the event of major power line (100 kV+) short, then this can causes severe voltage disturbances. Usually, at this power level, multiple feeders from different directions are connected in parallel to converge onto each substation. So, if one trips out, the power will keep flowing through the others without interruption. However, during the short circuit, before the breakers trip out, the voltage can show severe dips, and this dip will go through all the substations and to every device supplied from them.

Note that different types of light have different sensitivities to flicker. Low voltage halogen is extremely resistant. Regular incandescent is quite sensitive. CFLs vary depending on design, and LEDs also vary (but tend to be very good)
 
I see this flicker at all different times of the day. I can't imagine equipment shorting out all the time everyday even at 2AM.
 
14AWG wiring!!! (according to some people...)

Probably a less than desirable connection (loose wire nuts, breaker set screw, breaker seating, wire to outlet, wire to lamp socket, etc) in the circuit combined with a large device in the house kicking on creating a sag.
 
I'm wondering if it's the fridge in the house. The freezer and fridge in the garage don't do this when the garage lights are on there is no flicker.
 
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