What Is Happening When the Lights Dim When the AC & Appliances Come On?

Circuit Overload

• A circuit overload may be causing the lights to dim. If the lights are on the same circuit as the air conditioning and the appliances in question, the power overload will weaken the lights. This is more prevalent in older homes than in newer construction. You can quickly determine if a circuit overload is the problem by turning off the air conditioner’s circuit breaker. If the lights and appliances go out as well, they are all on the same circuit and you should get an electrician to install the air conditioner and large appliances on separate circuits.

Wiring

• The lights may be dimming because of wire connectivity issues, especially if the problem began recently. According to Wurtsboro Electric Service in New York, this problem is more evident in the high-demand summer months, when the wires undergo more stress. In addition, if your main circuit breaker panel is on one side of the house and the air-conditioning unit on the other side, the wire may be too long, rendering it unable to sufficiently power the air conditioner startup, according to Code Electric of Iowa. An electrician can secure a loose connection, replace faulty wiring or determine if the wire length is too long.

Transformer

• An overloaded utility transformer may cause several electrical problems, including dimming of the home’s lights, blown lights or lights that burn too brightly. The utility line coming from the street may be overloaded as a result of a large number of homes in the area. Call your utility company for a check of the lines. The company may not be required to correct the situation, however, because the power fluctuations may fall within the acceptable range.

Fuse Box

• A problem with the fuse box can also cause the lights to dim when the AC and other appliances are on. Older homes with fuse boxes, as opposed to circuit breakers, may not have the capacity to power today's commonplace household electrical needs. The fuses do not generate enough power to sufficiently operate the lights, air conditioning and appliances at once. An electrician can upgrade your fuse box.