Dimming Lights


Old 07-24-04, 02:36 PM
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Dimming Lights

Maybe a silly question, but when my central air conditioning unit comes on, the lights in the house momentarily dim slightly. Is this normal and OK?
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Old 07-24-04, 02:51 PM
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That is a normal occurance. On start up, the compressor motor on your A/C draws a very high amount of current (known as inrush current.) This inrush creates a large draw on the system, which often leads to a dimming of your lights. As long as it isn't causing your electronics (computer, TV, etc.) to shut down it isn't a big issue. The problem can be reduced (though generally not eliminated) by using oversized wires to feed the A/C. For the most part, the expense of doing that isn't worth it, as the problem will still exist just at a reduced level. However, if you are experiencing problems with electronics shutting down, it may be a worthwhile solution.
Old 07-24-04, 03:32 PM
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Although as CS says, it may be nothing, I would recommend having the power company check the tightness of the connections on their side (usually free), and if that doesn't mitigate the problem, have an electrician check the connections in you main panel. Oversizing the feed wires to the air conditioner will reduce the voltage drop to the air conditioner, but it won't do anything about the voltage drop to the rest of the house when it kicks in. Dimming lights in the rest of the house implies excessive resistance in the connections leading up to your breakers.

Sometimes the power company does not upgrade their equipment to keep pace with growth. And sometimes connections just come loose. In any event, my experience is that a phone call to the power company resolves the issue at least half the time. Worth a try.

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