Flickering Lights or Power Problems During an Outage

Generator power should feel like utility power. If your lights flicker, dim when a big appliance kicks on, or cut out while the generator is running, something in the chain — sizing, load, or the transfer switch — isn't keeping up. Here's how to tell the causes apart.

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Overload is the first suspect

A generator has a fixed capacity, and when demand exceeds it, voltage sags: lights dim, motors strain, and the unit may surge or shut down to protect itself. This is common with portable generators running too many circuits at once, and with standby units that were sized for essentials but are now asked to run everything, including central air. Note what was running when the problem appeared — that list is gold for a technician.

Transfer-switch trouble looks similar

A transfer switch that doesn't fully engage, or a connection that has loosened over time, can cause flickering, partial power, or circuits that drop in and out. Because the switch sits between your home and two power sources, its problems are not homeowner-serviceable: don't open it, and don't try to force it. Note which circuits are affected and whether the problem is constant or intermittent.

Brief dips when big loads start are different

A short dimming when a well pump or air conditioner compressor starts is normal on many systems — motors draw a surge of current at startup. What isn't normal is sustained flickering, repeated dimming, or the generator hunting and surging under a steady load. The line between the two is worth describing carefully to a technician.

What to do while it's happening

Shed load: switch off non-essential circuits and big appliances, and see whether the problem settles. If it doesn't, if you smell burning, or if power is cutting in and out, shut the generator down if you can do so safely and call a professional. Never backfeed through an outlet to work around a transfer problem — a proper hookup makes backfeeding physically impossible for a reason.

Common questions

Why do my lights dim when the air conditioner starts on generator power?

Compressor motors draw a large surge at startup, which briefly pulls voltage down. A short dip at startup is common; sustained flickering or dimming is not, and points to sizing, load management, or a transfer-switch issue worth having checked.

Is flickering dangerous, or just annoying?

It can be both. Sustained voltage problems can damage motors and electronics, and flickering caused by a failing connection is a fire risk. Don't ignore it — shed load, note the pattern, and get it diagnosed.

Could my generator just be too small?

Possibly. A unit sized for essentials will struggle if it's asked to run a whole home, and homes change — a new heat pump, a finished basement, an EV charger — without the generator growing with them. A load calculation tells you whether sizing is the problem before you spend anything.