Checking a 3 phase power supply isn’t just about confirming voltage—it’s about making sure your system is balanced, safe, and delivering power the way it should. Whether you’re managing a workshop, running a commercial kitchen, or just installed a 3 phase EV charger at home, knowing how to verify your power supply properly can save you from costly damage or downtime.
Step 1: Understand the Basics First
Before testing anything, it’s important to understand what you’re checking:
A 3 phase power system delivers electricity using three active wires, each carrying current at a different point in the sine wave (120 degrees apart). This creates a more stable and continuous flow of power compared to single phase, which only uses one live wire.
You’ll typically see:
- Around 400V between any two phases
- Around 230V from any phase to neutral
3 phase power is commonly used in:
- Large residential properties with ducted air con or EV chargers
- Commercial kitchens, workshops, and medical clinics
- Industrial setups running motors, lifts, and large HVAC systems
Knowing these fundamentals helps you make sense of the numbers when it’s time to test.
Step 2: Identify the Power Source
Make sure you know where your 3 phase system starts and ends:
Before you pick up a meter, locate the main switchboard or sub-board that distributes 3 phase power. You should clearly see markings or breakers labelled L1, L2, and L3 (sometimes called Phase A, B, and C). In some cases, coloured cables—red, white, and blue—will indicate the phases.
If you’re checking at the meter box, make sure it’s safe and accessible. If you’re testing at an appliance (like a motor or EV charger), trace the circuit back to the board and confirm it’s on a 3 phase supply—not split single phase.
Step 3: Use the Right Testing Equipment
Only proceed with proper tools and knowledge—safety is critical:
To check a 3 phase system safely, you’ll need:
- A multimeter or voltmeter rated for at least 600V
- Insulated tools and PPE, including safety gloves and eyewear
- A clamp meter if you want to test current draw on each phase
- An understanding of your limits—don’t touch live terminals unless qualified
If you’re not trained, avoid opening switchboards or testing live terminals yourself. A wrong move can cause serious shock, damage, or fire. Even if the readings look simple, testing 3 phase power involves working around high voltage and energy potential.
This is one job where experience and licensing matter. At Powerhub Electrical, we carry out 3 phase testing using calibrated, high-accuracy meters and follow all safety standards to the letter.
Step 4: Check Phase-to-Phase Voltage
This confirms whether all three phases are live and balanced:
Once you’ve identified the active lines (L1, L2, L3), the first key test is voltage between each pair of phases. Using a multimeter set to AC voltage:
- Measure between L1 and L2
- Then L2 and L3
- Then L1 and L3
Each reading should be roughly 400 volts (give or take a few volts). If any reading is significantly lower—or zero—one of your phases may be down, disconnected, or faulty. This is a common issue in large buildings or commercial setups where only two phases are energised.
Consistent voltage across all pairs confirms that all phases are live and balanced from the supply end.
Step 5: Check Phase-to-Neutral Voltage
Confirms correct phase voltage and system grounding:
Next, test each phase wire to the neutral terminal:
- L1 to Neutral
- L2 to Neutral
- L3 to Neutral
Each should return around 230 volts, with slight variance depending on load and supply conditions. If one phase shows a much higher or lower reading, or no reading at all, it could indicate:
- A disconnected phase
- A faulty neutral connection
- An imbalance affecting system stability
These faults can affect appliances, trip protection devices, and cause motors to overheat, especially if left undetected.
This step also helps identify neutral failures, which are rare but serious, as they can cause appliances to receive incorrect voltages and fail.
Step 6: Look for Voltage Imbalance
Even small differences can affect motor performance and safety:
Once you’ve recorded all phase-to-phase and phase-to-neutral readings, compare the numbers:
- Is there more than 2% variance between any phase voltages?
- Are any phases consistently lower or unstable under load?
A well-balanced system will show similar voltage levels across all phases. If one line drops under load or shows a consistent deviation, that may point to:
- Uneven distribution of loads across the phases
- Loose terminals or corroded connections
- Overloaded circuits on a specific phase
Unbalanced 3 phase systems can shorten the life of motors, trip RCDs, and increase your energy costs. For commercial setups, imbalances can even lead to production downtime or equipment failures.
When we carry out 3 phase testing at Powerhub, we log voltage and current data to identify imbalances early, before they become costly problems.
Step 7: Check Load Conditions (Optional)
If you’re checking under real-world load, here’s how to take it further:
For more advanced testing, especially in commercial settings, you can check how much current each phase is drawing while equipment is running. This is done using a clamp meter.
Clamp around each phase wire (L1, L2, L3) one at a time while motors, lights, or appliances are operating. The readings should be:
- Similar across all three phases (if loads are balanced)
- Within the circuit’s rated limits
- Stable — not fluctuating rapidly
A large imbalance between the phases could mean:
- Uneven load distribution
- A faulty motor
- A circuit overloaded on one leg
This step isn’t always necessary for basic checks, but it’s crucial in industrial sites or any setup with heavy equipment. It helps diagnose long-term performance issues before they cause failures.
Step 8: Record & Interpret Your Results
Don’t just test—make sense of what you’re seeing:
It’s not enough to take readings—you need to know what they mean. After completing all tests, note down:
- Phase-to-phase and phase-to-neutral voltages
- Current readings (if taken)
- Any signs of imbalance, flickering, or instability
Look for consistency. If the numbers vary wildly, or one phase is consistently out of spec, there may be an issue with the supply, the load, or the wiring.
At Powerhub, we record and explain all findings clearly—so clients know exactly what’s going on, and what needs fixing.
When to Call a Licensed Electrician
Some things are best left to the pros—especially with 3 phase systems:
Call a licensed electrician if:
- You get zero voltage on one or more phases
- You notice burning smells, buzzing, or visible damage
- Readings vary significantly and you’re not sure why
- Circuit breakers or RCDs trip during testing
- You don’t feel confident working around live terminals
Powerhub Electrical handles 3 phase testing, repairs, and upgrades across Sydney—safely, legally, and efficiently.
Need Your 3 Phase Power Checked in Paramatta?
If you’re unsure about your supply, planning an equipment upgrade, or just want peace of mind, Powerhub Electrical is here to help. Call 0400 332 331 to book a 3 phase power check today. We’ll test your system, diagnose faults, and make sure your setup is safe, balanced, and compliant, before it becomes a problem.
