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Why do my lights flicker?

Q: The lights throughout my house flicker whenever I turn on an appliance. Why? Two electricians have checked the wiring. One had no clear recommendations, and the other recommended replacing the service panel. The utility has disavowed any responsibility for the problem. Should I be concerned about the condition or safety of the house wiring?

A: Clifford A. Popejoy, an electrical contractor in Sacramento, California, replies: A slight flicker is fairly normal when a big motor load like an air conditioner or washing machine starts. If all the lights flicker in sync (instantaneously dim, then return to normal) when a small appliance is turned on, it is a system problem. The cause lies somewhere between the branch circuit breakers in the main breaker panel and the utility pole.

If the flickering also is experienced by your neighbors and is more severe when all the air conditioners in the neighborhood are running, the problem could be that the drop, the transformer, or the distribution grid isn’t able to supply enough energy. Another possibility is loose connections at the main breaker. An electrician will be able to find and fix a problem in your panel, or rule it out and get the utility to investigate its side. This situation is urgent: If the problem is in the main panel, someday it will fail catastrophically.

It’s a different problem if some of the lights dim and others get brighter when an appliance starts. This symptom points to a compromised neutral connection between the main panel and the utility transformer. This is an immediate danger, because if the utility neutral connection is lost completely, some appliances will be subject to voltages much higher than the normal 120v, damaging or destroying the appliances and possibly starting a fire. Most utilities will respond without delay if you describe a condition that suggests a loose neutral.

Will a new service panel solve the problem? Maybe, if it’s a bad meter socket or a bad main breaker, or if the hot buses are corroded beyond repair. But a new service panel won’t help if the problem is a loose neutral, or a bad utility transformer or drop-wire connection.

From Fine Homebuilding 164, pp. 106 July 1, 2004

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