The electrical system of a home, especially an older home, can be difficult to diagnose and repair. Flickering lights are a typical complaint from homeowners, and can reflect underlying problems of varying significance. However, keep in mind some flickering of lights due to electrical resistance is normal, and almost unavoidable in many older homes and neighbourhoods.
Loose Circuit Connections
Loose circuit connections are among the most common causes for lights flickering in a home. This is potentially the most dangerous problem, as a loose connection leads to high resistance, which can lead to arcing and point heating, a fire hazard.
A Breaker Switch Starting to Fail
A breaker switch just about to fail is another common cause for flickering lights. This is of concern, but not as big a deal, as you just have find and replace the defective switch.
High Electrical Load Appliances
Appliances with high electrical loads are another typical cause of flickering lights. Large toaster ovens, refrigerators, air conditioners or sump pumps are common high-load appliances. If a large appliance has a bad motor and is straining to draw current, the flickering can become problematic. This is especially a problem in older homes. Putting individual appliances on their own 240 V circuit will often significantly alleviate this flickering.
Heavy Electrical Loads in Your Neighborhood
Another common reason for flickering lights is pretty much out of your control--heavy electrical demand in your neighbourhood. Whether it is a hot summer afternoon and everybody has their AC on, or you just live in a dense urban neighbourhood, you share a local transformer with at least a few neighbours, and when the load is high, everyone's electrical system is affected.