Common Causes of Flickering Lights

Q. In my kitchen and in my basement, certain lights flicker every 60 seconds or so. It is almost imperceptible, but it does happen, lasting a fraction of a second, if that. The basement lights are recessed cans on multiple switches and the kitchen lights are a set of three pendant lights on one switch. They are on separate circuits from each other. Both my basement and kitchen were recently renovated, with the electrical work done by electricians. However, the flickering only started in the last month or so, whereas the work was done about six months ago and I never noticed any flickering until now. What does the flickering mean? Could a staple or screw be making contact with a wire?

A. Flickering of lights is normal, and it happens for a number of reasons.

1. Wires have resistance, meaning that when current flows through them, some amount of voltage gets 'used up' to make the current flow. This means less voltage for your various loads (lights, toaster, etc.). If you have loads that turn on and off, then the voltage supplying your lights will change, and the lights will flicker.
2. Many loads have 'inrush current,' and draw lots more current when they are first turned on; on startup they will cause significant voltage drop in the supply.
3. Proper design of your electrical system can minimize but not eliminate flicker. For example, large loads should be on their own circuits, and should be on 240V circuits. Since your main supply wires have some resistance, you will still get some flicker even when these loads are on different circuits. Properly designed, you may not be able to notice the flicker, but it will still be there.

That said, flickering of lights is essentially a measure of the resistance of the circuit that feeds both the lights and the load causing the flickering. If the flickering is large, or if the amount of flicker has changed without any intentional changes in the electrical system, then this could be an early indication of a problem. The possible issues (some benign, some not) include:

1. A circuit connection getting loose, since this becomes a high resistance point. This is the most dangerous, since the high resistance point means point heating.
2. A switch starting to fail. This is almost as bad as A, but contained inside the switch.
3. A motor that is 'hard starting'; you may have no problems with your electrical system, but an appliance may have something like a bearing failure, which causes the motor to work harder on startup, drawing more current and making a more noticeable flicker.
4. An unexpected but correctly functioning load, i.e., a sump pump.
5. Loads at neighbors' houses. In general you share a transformer with several neighbors, and since you share a circuit with them, their loads will affect your electrical supply.

If the flicker is significant, or has changed in unexpected ways, you should investigate. Some of this investigation is easy DIY stuff (trying to correlate the flicker to a particular appliance, listening for buzzing or crackling sounds at your breaker panel when loads start) and some is stuff that should be left to an electrician. If the flicker is annoying, or is getting worse, I would suggest contacting an electrician and having them measure what sort of voltage drop you are seeing when various loads turn on.

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