Why Do My Lights Flicker When I Turn On the Air Conditioner?

If your lights dim or flicker every time your air conditioner kicks in, you are not imagining it. This is one of the most common electrical concerns we hear from Melbourne homeowners, particularly during summer when split systems and ducted units are running hard. In most cases, a brief flicker when the AC compressor starts is normal and not a sign of danger. But in some cases, it indicates a wiring problem, an overloaded circuit, or a switchboard that cannot handle the electrical demand of your home.

This guide explains what causes lights to flicker when the air conditioner turns on, how to tell the difference between normal behaviour and a genuine problem, and what can be done to fix it. As Melbourne electricians (REC 33210), we see this issue regularly across the inner suburbs, particularly in older homes that were wired long before air conditioning became standard.

Why Air Conditioners Cause Lights to Flicker: Inrush Current Explained

The reason your lights flicker when the air conditioner starts is something called inrush current, also known as startup current or locked rotor current. When the compressor motor in your air conditioning unit first starts up, it draws a surge of electrical current that is significantly higher than its normal running current. This surge can be four to eight times the normal operating current of the unit and typically lasts for a fraction of a second to a few seconds.

For example, a typical split system air conditioner might draw 8 to 10 amps during normal operation. But during that initial startup moment, it can draw 40 to 60 amps or more. This sudden spike in current draw causes a temporary voltage drop on the circuit and, depending on the wiring configuration, across other circuits in the home as well.

When the voltage drops momentarily, lights connected to the same circuit or to circuits sharing the same feed from the switchboard will dim briefly. This is the flicker you see. Once the compressor is up to speed, the current draw drops back to normal levels and the voltage stabilises. The lights return to their normal brightness.

This effect is more noticeable with certain types of lighting. LED globes and downlights are particularly sensitive to voltage fluctuations, which is why you might notice flickering more in a home with LEDs than one with older halogen or incandescent globes. The LED driver circuits respond to voltage changes in ways that can make even small fluctuations visible.

When Flickering Is Normal

A brief flicker or dim when the air conditioner compressor starts is generally normal behaviour. Here is what normal looks like:

The flicker lasts less than a second. The lights dim briefly and return to full brightness almost immediately. This corresponds to the compressor motor reaching operating speed and the inrush current subsiding.

It only happens at startup. The flickering occurs only at the moment the compressor kicks in, not during continuous operation. If your air conditioner has an inverter compressor (most modern split systems do), you may notice a brief flicker when the unit first starts but not during speed changes, since inverter compressors ramp up gradually rather than starting abruptly.

The dimming is slight. The lights dim noticeably but do not go extremely dark or flash on and off. A slight dimming that is visible but not dramatic is within the range of normal voltage drop from inrush current.

It only affects some lights. Typically, lights on the same circuit or on circuits physically close to the air conditioner circuit in the switchboard are most affected. Lights on distant circuits may not be affected at all.

When Flickering Indicates a Problem

While some flickering at AC startup is normal, there are several signs that indicate a more serious electrical issue that needs professional attention:

The lights dim significantly or go very dark. If the lights dim dramatically rather than just flickering slightly, this suggests a more substantial voltage drop than normal. This could indicate undersized wiring, a poor connection, or a supply issue.

Flickering lasts more than a second or two. If the dimming persists for several seconds or continues intermittently while the AC is running, this is not just inrush current. It could indicate a loose connection, a failing compressor motor drawing excessive current, or a wiring fault.

Flickering happens during AC operation, not just at startup. If lights flicker randomly while the air conditioner is running (not just at the moment it starts), this points to a different issue entirely. Possible causes include loose wiring connections, a faulty neutral connection, or problems with the electricity supply from the street. For more on general light flickering causes, see our comprehensive guide on flickering lights in Melbourne homes.

Multiple appliances are affected. If the air conditioner starting also causes other appliances to behave oddly, such as clocks resetting, computers restarting, or other motors slowing down, this suggests a systemic issue with the home’s electrical supply or wiring.

You hear buzzing or humming from the switchboard. Unusual sounds from the switchboard when the air conditioner starts can indicate loose connections, an overloaded circuit breaker, or components that are under stress. If you notice a burning smell from your switchboard, turn off the power and call an electrician immediately.

Circuit breakers trip when the AC starts. If the air conditioner starting causes a circuit breaker to trip, the circuit is overloaded or there is a fault. This is not normal and needs investigation. See our guide on why your power keeps tripping.

Common Causes of Excessive Voltage Drop

When the flickering goes beyond what is normal, several underlying issues could be responsible:

Air conditioner on a shared circuit. In many older Melbourne homes, the air conditioner was added to an existing power circuit rather than being installed on its own dedicated circuit. When a high-draw appliance like an AC compressor shares a circuit with lighting or other power points, the inrush current has a much greater impact on the circuit voltage. The fix is a dedicated circuit from the switchboard to the air conditioner.

Undersized wiring. Homes built in the 1950s to 1970s were wired with cable sizes appropriate for the electrical loads of that era. Melbourne homes in suburbs like Fitzroy, Collingwood, Richmond, Northcote, and Hawthorn often have original wiring that is undersized for today’s demands. When you add a modern air conditioner to wiring that was designed for a few lights and a radio, voltage drop under load is inevitable.

Loose connections. Over time, wiring connections at the switchboard, at junction points, and at the air conditioner isolator can loosen. A loose connection creates resistance, which increases voltage drop and can generate heat. This is a fire risk and needs to be identified and repaired by a licensed electrician.

Long cable runs. Voltage drop increases with the length of the cable between the switchboard and the load. If your air conditioner is installed at the far end of the house from the switchboard, the longer cable run contributes to greater voltage drop. This is accounted for in proper electrical design under AS/NZS 3000 (the Wiring Rules), but may not have been considered if the AC was installed as an afterthought.

Switchboard limitations. Older switchboards, particularly those with ceramic fuses or early-generation circuit breakers, may not have the capacity to handle the demands of a modern household. If your switchboard is at or near its rated capacity, the addition of a high-draw appliance like an air conditioner pushes it beyond its design limits. A switchboard upgrade may be needed. You can check the current state with our guide on switchboard replacement costs in Melbourne.

Supply-side issues. In some cases, the voltage drop is occurring on the supply side, in the cabling between the street and your meter, or in the distribution network itself. This is the responsibility of your electricity distributor (CitiPower, Powercor, Jemena, AusNet Services, or United Energy, depending on your Melbourne suburb). If supply-side voltage is consistently low, your distributor should be contacted to investigate.

Dedicated Circuits for Air Conditioning Units

The correct installation practice for any air conditioning unit, whether it is a split system or ducted, is to run it on a dedicated circuit from the switchboard. A dedicated circuit means the air conditioner has its own circuit breaker, its own cable run from the switchboard to the unit, and does not share the circuit with any other appliance or lighting.

The benefits of a dedicated circuit include:

Reduced voltage drop. Because the circuit is not shared, the inrush current of the compressor does not affect other circuits in the home. Lights on separate circuits will not flicker when the AC starts.

Proper cable sizing. A dedicated circuit can be wired with the correct cable size for the air conditioner’s rated current draw, including allowance for inrush current and cable length. This ensures the voltage drop stays within the limits specified by AS/NZS 3000.

Independent circuit protection. The air conditioner has its own circuit breaker sized appropriately for the unit. If a fault occurs in the AC circuit, it trips its own breaker without affecting the rest of the home’s power.

Safety switch (RCD) protection. The dedicated circuit can be protected by its own safety switch, providing earth leakage protection specific to the air conditioner installation. This is particularly important for outdoor units where moisture exposure is a factor.

If your air conditioner was installed without a dedicated circuit, this is a straightforward job for a licensed electrician. It involves running a new cable from the switchboard to the air conditioner location, installing a new circuit breaker (and RCD if not already covered), and reconnecting the air conditioner to the new dedicated circuit.

Signs Your Switchboard Cannot Handle the Load

If your lights flicker with the air conditioner and you also experience any of the following, your switchboard may be at or beyond its capacity:

Circuit breakers trip frequently. If breakers trip regularly, especially when multiple high-draw appliances are running simultaneously (air conditioner, oven, dryer, electric hot water), the switchboard is overloaded.

The switchboard feels warm. A switchboard that is warm or hot to the touch indicates connections that are under stress. This is a fire risk and needs immediate attention.

You have added appliances since the switchboard was installed. If the switchboard was installed 20 or 30 years ago and you have since added air conditioning, an EV charger, a pool pump, or other significant loads, the switchboard may not have been designed for the total load you are now drawing.

You still have ceramic fuses or rewirable fuses. If your switchboard predates modern circuit breakers, it is almost certainly unable to safely handle modern electrical loads. A ceramic fuse box upgrade is essential.

What Carlin Co Can Help With

If your lights flicker when the air conditioner starts and you are not sure whether it is normal or a problem, Carlin Co (REC 33210) can assess the situation. We provide electrical assessments across Melbourne that include checking your air conditioner’s circuit configuration, measuring voltage drop under load, inspecting the switchboard for capacity and condition, and recommending any upgrades needed to safely handle your home’s electrical demand.

Common solutions we implement include installing dedicated circuits for air conditioning units, upgrading switchboards to handle increased loads, tightening or replacing loose connections, and upgrading undersized wiring on affected circuits.

We service Melbourne’s inner suburbs including Fitzroy, Collingwood, Richmond, Brunswick, Northcote, Carlton, Hawthorn, Kew, Prahran, South Yarra, and surrounding areas.

Call us on 0432 632 346 or email [email protected]. You can also book online here.

Frequently Asked Questions

Is it normal for lights to flicker when the air conditioner turns on?

A brief, slight dimming of lights when the air conditioner compressor starts is generally normal. This is caused by inrush current, a momentary surge of power that the compressor motor draws at startup, which can be four to eight times its normal running current. If the dimming lasts less than a second and is not severe, it is typically nothing to worry about.

Why do my LED lights flicker more than my old halogen lights did?

LED lights are more sensitive to voltage fluctuations than halogen or incandescent globes. The driver circuits in LED globes and downlights respond to even small voltage changes, making flicker more visible. This does not mean the underlying voltage drop is worse; it just means the LEDs make it more noticeable.

Does my air conditioner need its own dedicated circuit?

Yes. Australian Standards (AS/NZS 3000) require air conditioning units to be installed on dedicated circuits with appropriate cable sizing and circuit protection. If your air conditioner shares a circuit with lighting or other power points, this is non-compliant and contributes to flickering. A licensed electrician can install a dedicated circuit to resolve this.

Can flickering lights caused by the air conditioner damage my electronics?

Frequent or severe voltage fluctuations can potentially affect sensitive electronics over time. Computers, TVs, and other electronic devices can be stressed by repeated voltage drops. If the flickering is significant, using surge protectors on sensitive equipment is recommended while the underlying issue is being resolved.

How much does it cost to install a dedicated circuit for an air conditioner in Melbourne?

The cost of installing a dedicated circuit for an air conditioner typically ranges from $350 to $800, depending on the distance between the switchboard and the air conditioner, the cable size required, whether a new circuit breaker needs to be added to the switchboard, and access conditions (such as running cable through roof spaces or under floors). Contact us for a specific quote based on your property.

Related Services

If your lights flicker when your air conditioner starts, a dedicated split system electrical circuit can resolve the issue. In some cases, a three-phase power upgrade may be needed to handle the additional load. Our general electrician team can diagnose the cause and recommend the right solution.