Why Your Lights Flicker When the AC or Dryer Kicks On (and Whether It’s a Problem)

You’re sitting in the living room and every time the HVAC compressor cycles, the lamp flickers. Or the kitchen lights dim every time the microwave runs. In older Pittsburgh homes this is nearly universal, and it ranges from completely normal to a sign of real trouble. The symptom is the same. The cause determines whether you should ignore it, get it checked, or act on it today.

What’s actually happening

When a big motor (AC, dryer, pool pump, well pump, refrigerator compressor) starts up, it draws inrush current (often 3 to 6 times the running current) for a fraction of a second. That spike causes a brief voltage dip on the circuits sharing the same panel. Lights on those circuits visibly dim or flicker because they’re briefly running on slightly lower voltage.

A small, brief dip on start-up is normal. Even a new house with modern wiring has a tiny amount of it. The question is how much, how often, and which circuits are affected.

When it’s normal

You can usually ignore the flicker if:

• It only happens for a half-second when a big appliance kicks on, then everything recovers
• The dip is slight: you see a brief dim, not a noticeable darkening
• Only shared-circuit lights flicker, not every light in the house
• The appliances themselves start and run normally
• It’s been like this for years and nothing has changed

Older Pittsburgh homes with 100-amp service and long branch circuits almost all have some startup flicker. It’s noticeable but harmless.

When it’s worth looking at

Call an electrician if you see any of these:

• Every light in the house dims when the AC or dryer starts (not just one room)
• The dip lasts more than a second, or the lights stay slightly dim while the motor runs
• Flickering happens without any obvious trigger (no appliance kicking on)
• You hear a buzz or crackle from the panel or a switch
• You can smell warm plastic or melted insulation anywhere
• The flicker started recently and the house used to be rock-steady

A change in behavior is the biggest flag. If the house has always flickered mildly, fine. If it started in the last month, something has changed (a loose connection, a failing breaker, a degrading service drop) and it’s worth 30 minutes of inspection time.

What we check first

On a flicker diagnostic visit, we go through this list in order:

1. Main panel lugs and neutral: loose lugs on the incoming service cause the most dramatic whole-house flicker. We torque and inspect with an infrared camera.
2. Neutral connections at the service: a degraded or corroded neutral at the meter causes voltage imbalance and flicker on one leg only
3. Individual circuit breakers: breakers that have repeatedly been overloaded can develop loose internal contacts that show up as flicker
4. The big appliance’s circuit: is the wire gauge correct, is the breaker the right size, is the connection to the appliance tight
5. Shared-circuit overloads: sometimes a 15-amp circuit has the living room lights, the kitchen lights, and a window AC all on it, and each stress point adds up

About 70 percent of the time we find the problem at the panel. Another 20 percent is in the individual branch circuit or a loose splice in a junction box. The remaining 10 percent is on the utility side, which means Duquesne Light has to come out and repair the service.

The utility-side problem

If we test your voltage with a good meter and see the voltage dropping below 110V when a motor starts, or if we see unbalanced voltage between the two legs at the main panel, the problem is likely the service drop or the transformer feeding your block. In that case we open a ticket with Duquesne Light. They’ll send a truck, re-terminate the service, and usually that solves it.

Duquesne Light service calls for voltage complaints are free. If you’ve got a sustained flicker and nothing inside the house looks wrong, the call costs you nothing to make.

What fixes we see most often

• Retightening lugs: $150 to $300 service call, solves a surprising number of complaints
• Replacing a loose or aged breaker: $100 to $200
• Fixing a corroded neutral at the meter: $200 to $500 depending on whether the utility has to get involved
• Splitting overloaded circuits: $200 to $600 to add a new branch circuit and move high-draw loads onto it
• Full service upgrade: $2,800 to $5,500 if the whole service is undersized (rare, but happens in 100-amp older homes that now run modern electric loads)

When to act urgently

Flickering paired with any of these is an urgent visit:

• Warm breakers or warm panel surfaces
• Burning smells
• Browning around outlets or switches
• Lights that stay dim after the motor stops
• Repeated tripping of the main breaker

Those are signs of a failing connection that could overheat to the point of damage. Don’t wait for the weekend to call.

If you’ve noticed flicker and you’re not sure which bucket it falls into, take a short video with your phone when it happens and send it to us. Usually we can tell you in 30 seconds whether it’s worth a site visit or whether it’s just your house being old.

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Frequently Asked Questions

Why do my lights flicker when the AC turns on?

Most brief flickers at motor startup are harmless — the AC compressor briefly pulls 3–5× its running current, which drops voltage across the panel bus. If the flicker is pronounced, prolonged, or accompanied by dimming elsewhere, it points to a loose neutral, undersized service, or a failing compressor.

Is flickering lights a serious electrical problem?

It can be. Subtle flickers at motor startup are normal. But repeated flickering throughout the day, lights brightening unexpectedly, or burning-plastic smell are signs of a loose neutral connection at the panel or service entrance — a known fire risk that needs immediate attention.

Can aluminum wiring cause flickering lights?

Yes. Aluminum wiring connections loosen over time as the metal oxidizes and expands/contracts more than copper. Pittsburgh homes built 1965–1975 with solid aluminum branch wiring commonly show flickering, warm outlets, and failing switches. Pigtailing or full rewiring is the permanent fix.

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Related Reading from Our Pittsburgh Electricians

• When Your Pittsburgh Home Needs a Sub-Panel: Additions, Finished Basements, and Detached Garages

Need a Licensed Pittsburgh Electrician?

Renaissance Electric & Power Systems has been serving Pittsburgh homeowners since 2008 with licensed, insured work backed by our PA contractor registration (PA-032900). Whether you need a panel upgrade, EV charger installation, recessed lighting, or whole-home surge protection, we handle it start-to-finish.

Call 1-888-681-WIRE (9473) or request a free estimate.

Service areas: Pittsburgh, Mt. Lebanon, Upper St. Clair, Bethel Park, Peters Township, Fox Chapel, Sewickley, Robinson Township, McCandless, Franklin Park, Hampton Township, O’Hara Township, Edgeworth, Sewickley Hills, and Bell Acres.