Introduction

When testing and tagging portable appliances, under AS/NZS 3760, two of the most important tests are the insulation resistance test and the leakage current test. Both methods verify insulation safety but are suited to different portable appliances and and equipment.  

This article explains the difference between these two tests, and why AS/NZS 3760 outlines specific situations where a leakage current test must be used instead of insulation testing.

What is an Insulation Resistance Test?

An Insulation Resistance Test is a non-energised test used to measure the resistance of the insulation that separates the active and neutral wires from the earth. For single phase appliances, typically 500V DC is applied between the active conductors and earth, and the resistance value which is measured in ohms is recorded.

This test is:

• Performed while the appliance is powered off but ALL switches are turned on
• Designed to detect breakdown or deterioration of insulation
• Commonly used for Leads, Powerboards, Class I and Class II portable appliances and equipment

Under AS/NZS 3760, a resistance reading above 1 MΩ is typically considered a pass.

‍

What is a Leakage Current Test?

A Leakage Current Test is performed while the appliance is powered on, and it measures the actual current that may leak to earth during normal operation. This test requires the appliance to operate under normal 240 volt conditions and is a preferred method of testing for appliances and equipment with internal switches such as contactors and relays.

Leakage testing is required when:

• The appliance uses soft-touch switches or relays that require mains power
• Surge protection, LEDs or motors interfere with insulation readings
• Sensitive electronics may be damaged by 500V insulation tests

‍

What AS/NZS 3760 Says About Test Selection

As outlined in Clause 2.3.3.2 – Testing of Insulation in AS/NZS 3760:2010:

“Insulation shall be subject to a leakage current test oran insulation resistance test in accordance with Appendix E.”

The standard also notes:

“For equipment that contains single phase motors, or if an insulation test fails due to the presence of internal components such as LEDs, the leakage current test is the preferred option.”

And importantly:

“If the equipment must be energised to close or operate a switching device in order to test the insulation, then the leakage current test in accordance with Appendix E shall be performed.”

This ensures you are using the safest and most accurate testing method for each appliance type.

‍

When to Perform a Leakage Current Test Instead

Perform a leakage current test when:

• The appliance has controls that only operate when the appliance is powered up
• An insulation test fails, likely due to internal components interfering with the reading
• Appliances with surge protection, sensitive electronics, or motor-driven parts

If the wrong test is performed, the appliance can fail the test even though there is no fault.

‍

Safety Tips When Performing a Leakage Test

Remember – the appliance will operate as per normal when performing a Leakage Test:

• Ensure the appliance is in safe working order before staring the test
• Avoid placing the earth return clamp on moving parts such as grinder discs, drill chuck or external metal parts that become hot such as a heat gun or toaster.
• Follow manufacturer safety procedures and test equipment guidelines

How to Identify Appliances That Require Leakage Testing

Determining whether an appliance has internal switches—such as relays, contactors, or soft-touch switches— can be tricky as they may only operate when the appliance is energised. If this is the case, a leakage current test (not an insulation resistance test) is required under AS/NZS 3760.

Here are some indicators an appliance may have internals switching components:

·        The Portable Appliance Tester Displays a Warning

If your Portable Appliance Tester (PAT) indicates that a switch has not been turned on even though you have switched the appliance on. This is a strong sign the appliance may contain internal switches. These internal switches may only activate when powered by 240V during normal operation.

·        It Does Not Power On Without Mains Power

Some devices will not activate until they are plugged in and switched on at the wall, even if the external power switch is turned on. These often use internal relays that require 240V to close the circuit.

·        It Has a “Soft-Touch” Power Button

Appliances like monitors, TVs, and office equipment often use electronic (capacitive or touch-sensitive) buttons rather than a mechanical on/off switch. These types of buttons usually require power before the appliance circuitry is activated.

·        It Contains Timers, Sensors, or Digital Displays

If the appliance includes programmable functions, displays, or sensors (e.g., a microwave with a digital clock or a heater with a thermostat), it likely uses internal relays or controllers that depend on live power.

·        It Fails the Insulation Test Without a Clear Fault

If an appliance fails an insulation resistance test and no physical damage or insulation issue is visible, it may be because internal electronics are interfering with the reading. In these cases, a leakage test should be used instead.

‍

Conclusion

Insulation and leakage current tests are essential to maintaining electrical safety. Understanding when and how to use each test ensures compliance and protects both people and property.

At ETA Training, our nationally recognised Test and Tag courses cover these procedures in full detail, ensuring participants understand both the theory and practical application of electrical safety testing.

‍

Ready to Learn Test & Tag the Right Way?

At ETA Training, we don’t just teach the basics — we train you in real-world electrical safety. Our nationally recognised Test and Tag courses cover both insulation and leakage testing in detail, giving you the confidence to handle any appliance type correctly.

• Practical, hands-on instruction
• Fully compliant with AS/NZS 3760
• Choose in-person or online learning

Courses delivered weekly across Perth or available onlineAustralia-wide.

Explore our In-Person Test & Tag Course
Explore our Online Test & Tag Course