A leakage test measures the small amount of electrical current that escapes from an appliance while it is running, instead of returning through the neutral conductor as it should. It is one of the in-service tests set out in AS/NZS 3760:2022, and unlike an insulation resistance test it is carried out with the appliance energised and operating at its rated voltage. This article explains what earth leakage current is, what the test measures on each class of equipment, and the limits that apply.

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What is Earth Leakage Current?

Earth leakage current is the small amount of current that escapes an appliance to earth instead of returning along the neutral conductor. No insulation is perfect, so in every mains-powered appliance a very small current passes through the insulation, and through components such as filters and capacitors, and finds its way to earth. At low levels this is entirely normal.

It becomes a hazard when it rises. An increase in leakage current is one of the earliest measurable signs that insulation is breaking down, that moisture has entered an enclosure, or that internal wiring has been damaged. At sufficient levels the current can pass through a person who touches the equipment.

The same test is described in several ways. Earth leakage current test, leakage current test, run test, and load test all refer to the test carried out with the appliance operating under normal conditions.

What Does the Test Measure on a Class I Appliance?

On a Class I appliance, the leakage test measures the difference between the current flowing in the active conductor and the current returning in the neutral conductor. Class I equipment relies on basic insulation combined with a protective earth connection to its accessible metal parts, and that earth connection is the path escaping current tends to take.

In a healthy appliance those two figures are almost identical. Any difference between them represents current that has left the circuit by some other path, most commonly through the protective earth. That difference is the leakage current.

What Does the Test Measure on a Class II Appliance?

On a Class II appliance, the test lead is attached to any accessible metal parts and the tester measures the current flowing or leaking to those metal parts. Class II equipment has double or reinforced insulation and no protective earth connection, so there is no earth path to measure a difference against.

Class II equipment is generally manufactured with a non-conductive enclosure and is marked either DOUBLE INSULATED or with the square within a square symbol.

How Much Leakage Current is Acceptable?

AS/NZS 3760 sets the maximum allowable leakage current by equipment type:

• Class I appliances: 5 mA
• Class II appliances: 1 mA
• Extension leads, power boards (EPODs): 1 mA

A reading above the applicable limit is a fail. The equipment must be removed from service, fitted with an Out of Service tag, and not returned to use until it has been repaired and retested.

These figures are acceptance criteria for in-service testing. They tell you whether equipment already in the workplace is still safe to use, which is a different question to the design limits a manufacturer works to.

What is the Difference Between a Class I and a Class II Appliance?

A Class I appliance requires protective earthing of some of its accessible metal parts, while a Class II appliance does not, because it is protected by double or reinforced insulation instead. The distinction matters for testing because it changes both the measurement method and the limit that applies.

Class I equipment is protected by basic insulation between the live parts and the accessible metal parts, combined with earthing of those metal parts.

Class II equipment relies on the insulation alone. None of the accessible metal parts require protective earthing, because the double or reinforced insulation itself provides the protection.

Extension leads, power boards and EPODs are treated as their own category, and carry the tighter 1 mA limit alongside Class II equipment.

Why Does the Leakage Test Matter?

Leakage testing identifies deterioration that a visual inspection cannot see. Insulation breakdown, damaged internal wiring, moisture ingress and ageing components all show up as a rise in leakage current before they cause an electric shock or a fire.

It is also carried out with the appliance switched on and running at its rated voltage, which means it confirms the equipment operates correctly at the same time. If an appliance makes an unusual noise or produces an unusual smell during the test, it should be fitted with an Out of Service tag regardless of the reading.

When is a Leakage Test Carried Out?

AS/NZS 3760:2022 requires a leakage test where the equipment must be energised to close or operate a switching device in order to test the insulation. In practice that covers equipment with internal relays and contactors, soft-touch power buttons, timers, sensors and digital displays.

A leakage test can be carried out on any appliance, not only those that require it. Choosing correctly between the leakage test and the insulation resistance test is covered in detail in our guide to the difference between insulation and leakage testing.

Because the appliance operates during the test, the position of the earth return clamp matters. It should be kept clear of moving parts such as discs and chucks, and clear of parts that become hot.

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Where Leakage Testing is Taught and Assessed

ETA Training delivers nationally recognised test and tag training. The qualification is made up of two units of competency:

• UEECD0007 Apply work health and safety regulations, codes and practices in the workplace
• UEERL0003 Conduct in-service safety testing of electrical cord-connected equipment and cord assemblies

Training covers the classes of equipment, the tests that apply to each, correct operation of a portable appliance tester, interpreting and recording results, and the documentation a workplace is expected to keep. The practical component is where competency is demonstrated and assessed, working with real equipment and real test instruments under a qualified trainer.

No prior experience is required, and no electrical qualifications are needed to enrol.

Book Your Test and Tag Training

ETA Training delivers nationally recognised test and tag training across three Perth locations. Booking is completed online in four steps:

1. Book using the online course calendar. Choose the course, choose the day, and pay online via the secure booking portal at any time.
2. Complete online learning units in your own time. The link to complete online theory is emailed once the face-to-face session is booked. Online units must be completed before the date of the course.
3. Complete practical units at the training centres. Attend the classroom face-to-face session on the day and time of booking. Venues: Wangara, Welshpool, Treeby.
4. Receive your training certification. Once both pre-course theory and face-to-face practical components are completed, the certificate is issued. All certification provided by Allens Training Pty Ltd, RTO 90909.

Your Statement of Attainment is typically issued on the same day of successful course completion.

Visit the test and tag training course page to check session availability and book online. If you are located outside Perth and already own a portable appliance tester, the online test and tag course delivers the same certification.

First published 6 March 2024. Reviewed and updated 11 August 2026 against AS/NZS 3760:2022, with the earth leakage current limits confirmed by ETA Training.