The Circuit Detective    -  Blinking or Flickering

Disease can hit a tree like this, and flickering lights amount to a disease on a circuit
The Circuit Detective's Diagnostic Tree

What Causes Blinking or Flickering Lights?


If you have reached this page without beginning at the Start of the diagnostic tree, you may do better to start there.

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A slight flicker or very brief dimming that corresponds to appliances turning on (or stormy weather) can be normal, but if it has become more pronounced, read on.

Do not continue on this page if the kind of blinking you are seeing is:
  • A dimming or brightening that lasts more than three or four seconds; for that see Weird light behavior
  • Or made by an individual light bulb that has a defect. Check this by replacing that bulb.
  • Or made by a CFL (spiral, energy-saver) bulb(s) controlled by a dimmer switch. A dimmer is incompatible with most of these fluorescents and can make them blink.
  • Or a slight, infrequent flash a turned-off compact fluorescent (CFL, spiral) bulb may make at night if its switch is of the type that glows when off. This is normal.

The blinks I am dealing with here are due to a poor connection somewhere in your system. It is commonly at an outlet, light, or switch box, affecting part (not all) of one circuit. Knowing the extent of what is affected helps identify the likely locations of the loose connection. See The weak points of your system. If only all the light bulbs controlled by a dimmer switch blink, that switch is likely bad. (Fluorescent and low voltage lights need a specially rated dimmer.)

If one entire circuit is affected, the problem will likely be found at its breaker or its neutral connection in the panel. In fact, in my experience, these connections in the panel often ARE the source of the flicker, rather than other connections along the circuit. But if you get acquainted with the whole circuit and see that some lights on it never do blink, don't bother at the main panel, since this would mean a connection elsewhere on the circuit is the trouble.

If several circuits in the home suffer this simultaneously, a main wire connection at the panel, main (or submain) breaker, meter, or power company's line is probably compromised, and may eventually exhibit the wilder symptoms described in Weird light behavior.

In all of these possibilities, some arcing is going on at the poor spot during the blinking. This produces a little heat or sometimes enough heat to affect the appearance of the connections or wires at that point -- usually only visible when covers are removed and the connections are inspected. But opening many boxes in hope of seeing such signs is iffy, since there may be nothing very visible.

It can be difficult to pinpoint the location of an intermittent outage like a blink/flicker, until it has developed into a complete and final open, which it tends to do. In that case, but also with some chance of success ahead of that time, the procedures for dealing with an Open may locate the trouble spot by letting you try to produce or affect the blinking from various likely locations.

2005-2012 Larry Dimock

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