Lights that flicker when your air conditioner turns on are reacting to a sudden voltage drop on the circuit. The AC compressor draws a large surge of current at startup, typically three to five times its running load. This momentary demand pulls voltage away from other devices on the same circuit or panel, causing lights to dip briefly.
A quick, single flicker lasting less than a second is usually harmless. But flickering that is prolonged, severe, or spreading to multiple rooms signals a deeper electrical issue. Byrd Electrical provides switchboard upgrades, circuit installations, and electrical fault diagnosis across Melbourne and Bayside. This guide explains why it happens, when to worry, and how to fix it.
What Causes the Voltage Drop at AC Startup
Air conditioners are among the most power-hungry appliances in any Australian home. When the compressor kicks in, it needs a burst of energy to overcome the mechanical resistance of starting the cooling cycle. This initial surge is called inrush current.
In Australia, residential homes run on 240 volts. That’s double the 110-volt systems used in the United States, which means the current draw at startup creates a more noticeable effect on the circuit.
A typical split system draws 10 to 15 amps during normal operation, but can pull 30 to 45 amps for the first second or two at startup. A ducted system draws even more. When that surge hits, the voltage available to everything else on the panel drops momentarily. Your lights, being the most visually obvious indicator, show that drop as a flicker or dim.
In my 15 years working on electrical systems across Melbourne, lights flickering when the AC starts is one of the most common summer call-outs I attend. Most of the time, it’s manageable. Sometimes it’s the first sign of a switchboard or wiring issue that needs attention before it gets worse.
Is It Normal or Something to Worry About?
Not all AC-related flickering is a problem. The key is severity and duration. Use this table to assess your situation:
| What You’re Seeing | Risk Level | Likely Cause | What to Do |
| Brief dip (<1 second), lights return to full brightness immediately | Normal | Standard inrush current at compressor startup | No action required unless it worsens over time |
| Noticeable dimming lasting 1-3 seconds | Moderate | AC sharing a circuit with lights, or an undersized switchboard | Have circuits assessed by a licensed electrician |
| Severe dimming (lights drop to half brightness or lower) | High | Failing AC capacitor, undersized wiring, or weak supply connection | Stop using the AC and call an electrician |
| Flickering in multiple rooms or the whole house | High | Loose main neutral, switchboard fault, or network supply issue | Call an emergency electrician promptly |
| Flickering accompanied by buzzing, burning smell, or warm switchboard | Emergency | Arcing at a loose connection or overheating fault | Turn off the main switch. Call an electrician immediately |
| Flickering happens even when the AC is not running | Unrelated to AC | General wiring fault, loose connection, or failing component | Requires electrical fault detection |
If your situation matches the first row, you’re dealing with normal physics. Everything below that warrants investigation.
More: Are Flickering LED Lights Dangerous for Your Property?
Common Causes Behind AC-Related Flickering
When the flickering goes beyond a brief, harmless dip, one of these underlying issues is usually responsible:
AC Unit on a Shared Circuit
This is the number one cause I see in Melbourne homes. The air conditioner shares a circuit with lighting, power points, or other appliances instead of running on its own dedicated circuit. When the compressor starts and draws its inrush current, every other device on that circuit feels the voltage drop.
Homes in Cheltenham, Hampton, and Moorabbin that had split systems added after the original electrical fit-out often have this issue because the installer connected to an existing circuit rather than running a new one from the switchboard.
Undersized Switchboard
Many Melbourne homes built before 2000 have switchboards that were designed for a different era of electrical demand. They were sized for lights, a few power points, and maybe a wall oven.
Ducted air conditioning, multiple split systems, induction cooktops, and EV chargers weren’t part of the equation. When a modern AC system draws its startup load through a switchboard that’s already near capacity, the voltage sags across the entire panel.
Properties in Elsternwick, Caulfield, Malvern, and Armadale with original 1970s to 1990s switchboards see this frequently. A switchboard upgrade to a modern panel with adequate capacity and correctly rated circuit breakers resolves the issue permanently.
Failing AC Capacitor
The AC capacitor stores energy to help the compressor start smoothly. When the capacitor weakens or fails, the compressor draws more current from the household circuit to compensate.
This heavier draw causes a deeper, more prolonged voltage dip than normal. You’ll typically notice the flickering getting progressively worse over weeks. The capacitor itself is an air conditioning component, so an HVAC technician replaces it.
But if the heavier draw has been stressing your switchboard or wiring, an electrician should inspect for any resulting damage.
Loose Wiring Connections
A loose connection at the switchboard, at the AC isolator, or anywhere along the circuit increases electrical resistance. When the AC draws its startup surge through a loose connection, the resistance generates heat and causes a more pronounced voltage drop.
This is the most dangerous cause on this list because loose connections can lead to arcing and electrical fires. According to Energy Safe Victoria, fire brigades respond to more than 300 domestic electrical fires in Victoria each year, many originating at loose connections and degraded wiring.
Weak Supply Connection at the Meter
The connection between the electricity network and your home’s switchboard (the service cable and main fuse) can degrade over time. Corrosion, loose terminals, or an undersized service cable can restrict the flow of electricity into your home.
When the AC demands a large surge, the restricted supply can’t deliver it without the voltage dropping across the entire house. This type of issue requires both an electrician and, potentially, your electricity distributor to resolve.
Split Systems vs Ducted: Why It Matters
The type of air conditioning system in your home determines how much startup load your electrical system handles:
| AC Type | Typical Running Load | Typical Startup Surge | Circuit Requirement |
| Single split system (2.5-3.5kW) | 4-6 amps | 15-25 amps | Dedicated 20A circuit |
| Large split system (7-8kW) | 10-13 amps | 30-45 amps | Dedicated 20A or 32A circuit |
| Ducted system (10-14kW) | 15-22 amps | 45-70 amps | Dedicated 32A circuit with appropriately sized cabling |
A single small split system on a shared circuit might cause a barely noticeable flicker. A ducted system on the same undersized circuit can dim every light in the house.
Getting the circuit sizing right when the AC is installed is critical. If it wasn’t done the first time correctly, it can be corrected by running a dedicated circuit from the switchboard to the AC unit.
More: What to Do When Your Circuit Breaker Keeps Tripping?
Why Melbourne Homes Are Especially Prone
Melbourne’s climate, housing stock, and electricity network create conditions that amplify AC-related flickering:
Extreme Heatwave Demand
Melbourne’s summer heatwaves push electricity demand to extreme levels. During the January 2019 heatwave, when temperatures reached 42°C, Victorian electricity demand peaked at over 9,300 megawatts.
Air conditioning drives the vast majority of that spike. When millions of AC units across the network draw power simultaneously, the electricity distributors experience network-level voltage sag.
This means the voltage arriving at your home is already slightly lower than normal before your AC even starts. Your compressor’s startup surge then compounds an already-reduced supply, making the flicker more pronounced than it would be on a mild day.
Older Switchboards in Bayside and the South-East
Suburbs including Brighton, Sandringham, Beaumaris, Black Rock, and Bentleigh have large concentrations of homes built between the 1960s and 1990s. Many still have original switchboards that were never designed for the air conditioning loads these homes now carry. Some still have ceramic fuse boxes or early circuit breaker panels that are well past their safe working life.
AC Installations Without Electrical Upgrades
It’s common for Melbourne homeowners to have a split system installed by an HVAC company without involving an electrician to assess the switchboard capacity or run a dedicated circuit.
The installer connects the AC to the nearest available circuit, which often shares capacity with lights or power points. Everything works fine until the hottest day of the year, when every circuit in the house is loaded.
After resolving a persistent AC-related flickering issue at a Melbourne home, the Byrd Electrical team received this feedback: “I am so pleased with the work. Ben provided options and recommendations. It was easy to work and interact with absolutely no hassle. Will go back to them for any other electrical job.” Amita Shetty. Providing options and clear recommendations is how we approach every AC-related electrical issue.
Learn more about our team and approach.
How to Fix Lights Flickering When the AC Turns On
The right fix depends on the cause. Here’s what a licensed electrician typically recommends:
Install a Dedicated Circuit for the AC
If your AC shares a circuit with other devices, running a dedicated circuit from the switchboard to the AC unit is the most common and effective fix. This ensures the compressor’s startup surge doesn’t affect anything else in the house. Every AC unit should have its own dedicated circuit with a correctly rated breaker.
Upgrade the Switchboard
If the switchboard is undersized, outdated, or at capacity, a switchboard upgrade replaces the old panel with a modern board rated for current and future loads. This includes correctly sized circuit breakers, RCDs on every circuit, and enough capacity for air conditioning, cooking, EV charging, and other modern demands.
Tighten and Inspect All Connections
An electrical safety inspection checks every connection in the switchboard, at the AC isolator, and throughout the affected circuits. Loose connections are tightened or replaced, eliminating the resistance points that amplify voltage drop.
Have the AC Capacitor Tested
If the flickering has been getting worse over time and the electrical system checks out, the AC capacitor may be failing. An HVAC technician can test and replace the capacitor. Once the compressor starts smoothly again, the electrical draw returns to normal and the flickering stops.
Assess the Supply Connection
If the entire house dims when the AC starts and no internal fault is found, the supply connection between the network and the switchboard may need attention. Your electrician can coordinate with your electricity distributor to assess and upgrade the service cable if necessary.
Areas We Service
We service homes across Melbourne and Bayside, including Brighton, Sandringham, Hampton, Beaumaris, Black Rock, Cheltenham, Mentone, Moorabbin, Bentleigh, Highett, Elsternwick, Carnegie, Oakleigh, Caulfield, Glen Iris, Malvern, Camberwell, Armadale, Ormond, Toorak, Prahran, St Kilda, Elwood, and surrounding suburbs.
Get Your AC Circuit Sorted Before Summer
If your lights flicker every time the air conditioner kicks in, call Byrd Electrical on (03) 9000 0666. Licensed electricians, 24/7 emergency response, on time or we pay you $200, and a 100+ year extended workmanship guarantee on all work. Electrician of the Year 2024 and 2025. We install dedicated AC circuits, upgrade switchboards, and fix voltage drop issues across Melbourne and Bayside.
Frequently Asked Questions
Why do my lights flicker when the AC turns on?
The AC compressor draws a large burst of current at startup, typically three to five times its running load. This sudden demand causes a momentary voltage drop across your home’s electrical system, which shows up as a brief flicker or dimming in the lights.
Is it normal for the lights to dim when the air conditioner starts?
A brief dip lasting less than a second that returns to full brightness immediately is normal and caused by the compressor’s inrush current. If the dimming lasts longer, is severe, or affects multiple rooms, it indicates an electrical issue that needs professional assessment.
Can lights flickering when the AC starts cause a fire?
The flickering itself doesn’t cause a fire. But if the underlying cause is a loose wiring connection or an overloaded circuit, those faults generate heat that can lead to an electrical fire. Persistent or worsening flickering should be investigated by a licensed electrician.
Does my air conditioner need a dedicated circuit?
Yes. Every air conditioning unit should run on its own dedicated circuit from the switchboard. A shared circuit means the compressor’s startup surge affects other devices on the same circuit, causing flickering and potentially overloading the wiring.
Will a switchboard upgrade stop my lights from flickering when the AC runs?
In many cases, yes. An undersized or outdated switchboard can’t deliver enough capacity for modern air conditioning loads. Upgrading to a modern panel with correctly rated breakers and adequate capacity resolves the voltage drop issue and provides room for future electrical demands.
Should I call an electrician or an air conditioning technician?
Start with an electrician. Most AC-related flickering is caused by the electrical system (shared circuits, undersized switchboard, loose connections), not the AC unit itself. If the electrician confirms the electrical system is sound and suspects a failing capacitor, they’ll recommend an HVAC technician for that component.
