Lights flicker when the AC turns on because the compressor draws a large burst of electricity during startup, temporarily reducing voltage on the same circuit. This brief voltage dip causes connected lights to dim or flicker for a fraction of a second. A quick, subtle blink is usually normal. Anything longer or more noticeable signals an electrical issue.
Homes on the Central Coast, Newcastle, and Hunter Valley regularly hit extreme temperatures in summer, and AC systems work hard across the region. Restore Electrical provides licensed fault detection, switchboard upgrades, and dedicated circuit installations to resolve flickering light issues.
This guide explains when flickering is harmless, when it’s a warning sign, and what an electrician actually checks.
Is It Bad If Lights Flicker When the AC Turns On?
It depends on how long and how much they flicker. A brief, barely noticeable dip lasting less than a second is common in most homes and usually isn’t dangerous. But flickering that lasts longer than a second, dims the lights significantly, affects multiple rooms, or happens every single time the AC cycles on is telling you something isn’t right.
Here’s the difference. Australia runs on 240 volts, not the 120 volts used in the US. That means a voltage dip during AC startup is roughly twice as impactful here. A 5% voltage drop on a 240V circuit is a 12-volt swing, enough to make lights visibly dim.
On a 120V US circuit, the same 5% drop is just 6 volts, which is barely perceptible. So if you’re reading advice from American websites saying “it’s completely normal,” keep in mind your system is working at double the voltage. What’s harmless in the US can be a warning sign in an Australian home.
According to the Australian Government’s energy efficiency guide, heating and cooling accounts for 20 to 50 per cent of energy used in Australian homes. That’s a significant proportion of your total electrical load running through your switchboard every time the AC cycles on.
Normal vs Concerning: When to Call an Electrician
Use this table to work out whether your flickering is a harmless quirk or something that needs professional attention:
| What You’re Seeing | What It Means | Action Required |
| Brief, subtle dim lasting less than half a second | Normal inrush current from AC compressor startup | No action needed |
| Noticeable flicker lasting 1-2 seconds | Possible undersized wiring, shared circuit, or loose connection | Schedule an inspection |
| The lights dim significantly every time the AC starts | Switchboard at capacity, circuit overloaded, or weak neutral connection | Call an electrician soon |
| Flickering or dimming in multiple rooms simultaneously | Main supply or neutral issue, potentially at the switchboard or meter | Call an electrician promptly |
| Flickering accompanied by buzzing, crackling, or warm switches | Arcing, loose connection, or overheating. Fire risk. | Turn off the circuit immediately. Call an electrician |
| The lights go out completely when the AC starts, then come back on | AC may be tripping the circuit breaker. Overloaded circuit or faulty unit | Call an electrician. Do not keep resetting |
More: Voltage Fluctuations and Flickering Lights Explained
What Actually Causes Lights to Flicker When the AC Kicks In
Several different electrical issues can cause your lights to flicker when the air conditioner starts. Some are minor. Others need immediate attention. Here’s what I typically find when diagnosing this problem across Central Coast and Hunter Valley homes:
Inrush Current from the Compressor
Every air conditioner compressor draws a surge of current at startup, often 5 to 7 times its normal running load. A split system that runs at 10 amps might briefly pull 50 to 70 amps during that first half-second. This sudden demand temporarily lowers the voltage available to everything else on the same circuit, including your lights. On a properly wired system with adequately sized cables, this effect is minimal. On an older or undersized circuit, it’s much more noticeable.
AC Running on a Shared Circuit
Under AS/NZS 3000 (the Australian Wiring Rules), a fixed air conditioning unit should have its own dedicated circuit from the switchboard. But I regularly find older Central Coast homes where the AC was installed on an existing power circuit, sharing load with GPOs, lighting, or other appliances. When the AC starts on a shared circuit, everything on that circuit feels the voltage dip. If your lights only flicker in the room nearest the AC unit, this is likely the cause.
Loose or Corroded Connections
A loose wire at a switchboard terminal, a corroded neutral connection at the meter, or a degraded cable joint behind a wall can all amplify the effect of any load change. The connection creates resistance, and resistance under load causes a voltage drop.
The AC startup just makes the existing problem visible. According to NSW Fair Trading, faulty electrical equipment and wiring are a significant source of house fires in NSW.
Undersized Switchboard or Consumer Mains
Many homes on the Central Coast were built in the 1960s through 1980s with 40-amp or 63-amp main switches. A modern split system air conditioner can draw 15 to 25 amps on its dedicated circuit. Add that to an electric hot water system, a stove, a dryer, and general lighting, and the total load can approach or exceed the switchboard’s capacity.
When total demand gets close to the limit, voltage across all circuits drops during peak draw moments like AC startup. A switchboard upgrade resolves this by increasing the available capacity and adding properly rated circuits.
Failing AC Capacitor
The start capacitor in your air conditioner provides the initial energy boost the compressor needs to get moving. When a capacitor weakens with age, the compressor draws more current from the household supply to compensate.
This creates a larger and longer voltage dip than normal, making the flicker more pronounced. If the flickering has become gradually worse over time, especially over the summer season, a failing capacitor is a common cause.
Weak or Degraded Neutral Connection
The neutral conductor carries return current from your home back to the transformer. If the neutral connection at the meter board or the overhead service line is loose, corroded, or damaged, voltage can become unstable across all circuits.
You’ll notice lights flickering not just when the AC starts, but also when other large appliances cycle on and off. This is a serious issue that requires a Level 2 ASP electrician to assess the supply-side connection.
Why Central Coast and Hunter Valley Homes Are More Vulnerable
Location-specific factors make this problem more common in our region:
- Older housing stock with original wiring: Suburbs like Gosford, Woy Woy, Charlestown, and Wallsend have large numbers of homes built between the 1950s and 1980s. These properties were wired for far lower electrical demands than a modern household generates. Adding a split system to a 50-year-old switchboard without upgrading the wiring is like running a garden hose from a kitchen tap. It works, but not well.
- Summer heat is driving extended AC usage: The Central Coast and Hunter Valley regularly exceed 35°C in summer. According to the Australian Government’s Your Home guide, selecting and sizing cooling systems appropriately is critical for energy efficiency and electrical safety. Homes running AC for 8 to 12 hours a day put sustained stress on ageing electrical infrastructure.
- Coastal corrosion on connections: Properties in Terrigal, Umina Beach, Avoca Beach, and The Entrance are exposed to salt air that corrodes switchboard terminals, meter connections, and cable joints. Corroded connections create resistance, and resistance amplifies voltage drop. A connection that worked fine five years ago may now be the reason your lights flicker.
- Aftermarket AC installations on existing circuits: Many homes had split systems added by HVAC installers who connected the unit to the nearest available circuit rather than running a dedicated circuit from the switchboard. This is technically non-compliant with AS/NZS 3000 and creates exactly the kind of load-sharing problem that causes visible flickering.
What an Electrician Checks When You Report Flickering Lights
When I attend a flickering light call, the diagnostic process follows a specific order. Here’s what happens during a proper fault detection visit:
Switchboard Inspection
Visual check for signs of heat damage, corrosion, loose terminals, and overcrowded circuits. I check every connection for tightness and condition. A single loose neutral can cause flickering across the entire house.
Voltage Monitoring Under Load
Using a power quality analyser, I measure the voltage at the switchboard while the AC starts. A healthy system should show less than a 3% dip during startup. Anything above 5% indicates a wiring, connection, or capacity issue that needs addressing.
Circuit Identification
I verify whether the AC is on its own dedicated circuit or sharing with other outlets. If it’s shared, that’s the first thing to fix. Running a dedicated circuit from the switchboard to the AC unit is one of the most effective and straightforward electrical installations for resolving this problem.
Cable Size Verification
I check that the cable between the switchboard and the AC unit is rated for the unit’s maximum demand. An undersized cable creates a voltage drop under load and can overheat over time.
Neutral Integrity Testing
Using a loop impedance tester, I check the condition of the neutral path from the switchboard back to the supply transformer. A high reading indicates a degraded neutral that’s causing voltage instability.
Thermal Imaging
Where available, I use a thermal camera to scan the switchboard and AC isolator for hot spots. Loose connections generate heat before they cause visible damage, and thermal imaging catches them early.
After completing a diagnostic visit and electrical repairs for a homeowner on the Central Coast, the team received this feedback: “Incredible service!! They were extremely polite, time-efficient in their service and had excellent pricing. Couldn’t recommend their work more, will certainly be using again in future!” Hayley Verbunt. That’s the kind of experience we aim for on every call.
How to Fix Lights Flickering When the AC Turns On
The fix depends on the cause. In most cases, one or more of these solutions resolves the problem permanently:
Install A Dedicated Circuit For The AC
If the air conditioner is sharing a circuit with other outlets, running a new dedicated circuit from the switchboard eliminates the load-sharing problem. This is the most common fix and is required under AS/NZS 3000 for fixed air conditioning units.
Upgrade The Switchboard
If the switchboard is at capacity or older than 25 years, upgrading to a modern board with higher capacity, RCBOs on individual circuits, and correctly rated breakers provides a clean foundation for all your electrical loads.
Tighten Or Replace Corroded Connections
A loose or corroded terminal at the switchboard, meter, or AC isolator can be cleaned, tightened, or replaced. This is a straightforward repair that often makes an immediate difference.
Replace The AC Start Capacitor
If the compressor is struggling to start, an HVAC technician can replace the capacitor. This is an air conditioning repair, not an electrical one, but it reduces the startup current draw and eliminates the excessive flicker.
Upgrade The Consumer Mains Or Service Fuse
If the main supply cable or service fuse is undersized for total household demand, a Level 2 ASP electrician can upgrade it. This requires working on the network side of the meter, which standard electricians aren’t licensed to do. Learn more on our about page.
Install A Soft Starter On The AC Unit
A soft starter device reduces the initial inrush current by ramping the compressor up gradually instead of hitting full power instantly. This is a specialised solution typically used when the wiring and switchboard are otherwise adequate, but the startup surge is still too high.
When Flickering Lights Become an Emergency
Most flickering caused by AC startup is not an emergency. But these situations require immediate action:
Burning smell or visible scorch marks on the switchboard
Turn off the main switch immediately. Do not touch individual breakers. Call an emergency electrician straight away.
Lights flickering constantly, not just during AC startup
Persistent flickering unrelated to the AC cycling on suggests a neutral fault, a supply issue, or a deteriorating main connection. This needs urgent assessment.
Sparking or crackling sounds from the switchboard or wall outlets
Arcing is a fire risk. Turn off the circuit at the switchboard and get professional help immediately. According to SafeWork NSW, electrical safety alerts are regularly issued for exactly these kinds of hazards in residential settings.
The lights go completely out when the AC starts
If the AC is tripping the circuit breaker or safety switch every time it starts, the circuit cannot handle the load. Do not keep resetting the breaker. The repeated over-current stresses the wiring and connections.
Restore Electrical provides same-day diagnostic and repair services across the Central Coast and Newcastle for all residential electrical issues, including flickering lights, switchboard capacity problems, and AC circuit installations.
More: Why Does My Power Keep Tripping?
Areas We Service
Restore Electrical diagnoses and resolves flickering light faults, installs dedicated AC circuits, and provides switchboard upgrades across the Central Coast, Newcastle, and Hunter Valley, including Gosford, Terrigal, Erina, Umina Beach, Woy Woy, Bateau Bay, The Entrance, Avoca Beach, Kariong, Niagara Park, Lisarow, Ourimbah, Charlestown, Wallsend, Newcastle, Maitland, Lake Macquarie, Hunter Valley, and surrounding areas.
Get Your Flickering Lights Diagnosed by a Licensed Central Coast Electrician
If your lights flicker every time the AC kicks in, don’t ignore it. Call Restore Electrical on 02 4006 8326 for fast, accurate diagnosis and a lasting fix. Licensed electricians, same-day service, fixed upfront pricing, and a lifetime labour warranty on all work. $50 off your first service.
Frequently Asked Questions
Is it bad if my lights flicker when the AC turns on?
A brief, subtle flicker lasting less than half a second is usually normal. Flickering that lasts longer, dims lights significantly, or affects multiple rooms indicates an electrical issue that a licensed electrician should investigate.
Why do my lights dim so much when the air conditioner starts?
Your AC compressor draws a large surge of current at startup, temporarily reducing voltage. If the dimming is pronounced, the AC may be on a shared circuit, the wiring may be undersized, or a connection may be loose.
Does my air conditioner need its own dedicated circuit?
Yes. Under AS/NZS 3000, fixed air conditioning units in Australia require a dedicated circuit from the switchboard. If your AC shares a circuit with other outlets, a licensed electrician can install a dedicated line.
Can flickering lights when the AC starts cause a fire?
The flickering itself doesn’t cause fire. But the underlying cause, such as a loose connection, corroded terminal, or overloaded circuit, can generate heat and create a fire risk if left unaddressed.
Can an old switchboard make flickering worse?
Absolutely. Switchboards older than 25 years often lack capacity for modern AC units and appliances. Upgrading to a modern board with correctly rated circuits reduces voltage drop and eliminates flickering.
Should I call an electrician or an AC technician?
Start with an electrician. The cause is almost always electrical, not mechanical. If the electrician determines the AC unit’s capacitor has failed, they’ll advise you to contact an HVAC technician for that specific repair.
