I just bought a house and moved in last week. It was hot and humid up here in the northeast so I had an window A/C unit (5,000 BTU) cranking in one of the bedrooms. Every time the unit's compressor kicked in, lights in other parts of the house dimmed. This is my first home and I'm just starting to learn about the house's electrical and wiring. What would cause this flicker in the power?

Thanks in advance.

Scott

The ac unit probably has a nameplate amp draw of about 5-6 amps. When a air conditioner , which is a refrigeration motor, starts, it has a LRA ) locked rotor amperage) of 6-10 time the running load of 5 amps. This high draw is only for a brief moment, but this is the reason for the lights flickering. The high amp draw causes the voltage to sag proportional, so the lights, probabaly incandescent, react to the momentary voltage drop. The light output dims as the voltage dips, then the light output returns to normal as the voltage returns to normal.

The one way of eliminating the lights flickering would be to have a separate dedicated circuit, with no lights on that circuit, for the AC. This may not be practical to install, and really is not necessary, as long as you can live with the lights flickering. Just because the lights flicker, does not mean the circuit is overloaded. If the circuit was, the circuit breaker, which I suspect is a 15 amp for a bedroom, would trip.

Seems that if this is an older home, there is a bit more lighting on the circuit than if the home was newer.

Try to determine the total amount of load on the circuit the AC is using, to determine if the circuit is overloaded. Add up any device, appliance, lamp on the circuit, using the wattage or the amps. You need to get back to me to do the calcs, unless you know Ohm's Law to convert watts to amps and vice versa. The max load on a 15 amp circuit is 12 amps or 1440 watts.

Hope this helps, get back with any other questions you may have.

I'm still working on the mapping of the electrical system by the way... I hope to have it finished soon, I haven't been home long enough during daylight hours to kill all the power and map out the place.