Leakage current measurement is a core electrical safety test used to verify that products do not expose users to hazardous levels of current flowing through insulation or accessible surfaces. This article provides a professional overview of leakage current measurement methods based on standards such as IEC 60990, IEC 60335-1, IEC 62368-1, IEC 60601-1, and their UL and GB counterparts, covering test samples, measured parameters, measurement networks, procedures, limits, and typical applications.
Technical Overview
Leakage current is the unintentional current that flows from live (energized) parts to accessible parts, to the protective earth conductor, or to other circuits through insulation, stray capacitance, or filtering components. Although a small leakage current is unavoidable in most electrical equipment—particularly in devices fitted with EMI filters using Y-capacitors—excessive leakage represents an electric shock hazard and may also cause nuisance tripping of residual current devices.
In modern safety engineering, leakage current is generally subdivided into two distinct quantities defined in IEC 60990: protective conductor current, which flows through the earth conductor when the equipment is correctly connected, and touch current, which would flow through a person or animal touching accessible parts. Medical electrical equipment standards such as IEC 60601-1 further define earth leakage current, enclosure (touch) leakage current, patient leakage current, and patient auxiliary current, each with its own measurement circuit and limit.
The measurement itself cannot be performed with a simple ammeter. Because the human body presents a frequency-dependent impedance, standardized measurement methods use a resistor-capacitor measuring network that simulates human body impedance and weights the current components according to their physiological effect. The principal standards governing leakage current measurement methods include:
- IEC 60990 – Measurement of touch current and protective conductor current (the fundamental measurement method standard)
- IEC 60335-1 / GB 4706.1 – Household and similar electrical appliances
- IEC 62368-1 / GB 4943.1 – Audio/video, information and communication technology equipment
- IEC 60601-1 / GB 9706.1 – Medical electrical equipment
- IEC 61010-1 – Measurement, control and laboratory equipment
- IEC 60598-1 / GB 7000.1 – Luminaires
- UL 101, UL 1310, UL 60950-1 and related UL standards for the North American market
Testing Samples
Household and Similar Electrical Appliances
Refrigerators, washing machines, air conditioners, electric heaters, microwave ovens, kettles, cooking appliances, and other appliances rated up to 250 V for single-phase or 480 V for multi-phase supply are tested according to IEC 60335-1 and its product-specific Part 2 standards. Both Class I (earthed) and Class II (double-insulated) constructions are covered.
IT, Communication and Audio/Video Equipment
Power supplies, adapters, servers, monitors, routers, chargers, and multimedia equipment are evaluated for touch current per IEC 62368-1. Switch-mode power supplies with Y-filter capacitors are a primary focus, as their capacitive leakage increases with supply voltage and frequency.
Medical Electrical Equipment
Patient monitors, infusion pumps, electrosurgical units, imaging systems, and patient-coupled accessories require the most stringent measurement regime under IEC 60601-1, including patient leakage current measured through applied parts classified as Type B, BF, or CF.
Luminaires and Lighting Control Gear
LED drivers, fluorescent ballasts, and luminaires are tested for leakage current in accordance with IEC 60598-1, particularly where Class II construction or inaccessible control gear is involved.
Power Tools, EV Charging Equipment and Industrial Devices
Hand-held tools, motor-driven machinery, battery systems, and electric vehicle charging stations (per IEC 61851) are measured for protective conductor and touch currents, often under both normal and single-fault supply conditions.
Testing Items
Depending on the product standard, the following quantities are typically determined:
- Protective conductor (earth) current under normal operating conditions
- Touch current between accessible parts and earth, or between accessible parts and each supply pole
- Leakage current under single-fault conditions, such as interruption of the neutral conductor or reversal of supply polarity
- Earth leakage current, enclosure leakage current, patient leakage current, and patient auxiliary current for medical devices
- Leakage current at elevated supply voltage (typically 1.06 to 1.10 times rated voltage)
- Leakage current at normal operating temperature or after humidity conditioning, where specified
Testing Methods
Measurement Network and Instrumentation
The reference method is defined in IEC 60990. The equipment under test is supplied through an isolation transformer so that either supply pole can be grounded, and the current is measured through a calibrated measuring device consisting of a resistor-capacitor network that simulates the human body. The basic body resistance is on the order of 500 ohms, and additional parallel resistance-capacitance elements provide frequency weighting for the perception/reaction and let-go thresholds; overall effective impedance is typically between roughly 500 ohms and 2 kilo-ohms depending on the network selected. Commercial leakage current testers integrate this network together with a true-RMS or peak-reading voltmeter, allowing direct readout in milliamperes or microamperes.
General Test Procedure
- Condition the sample as required: operate the appliance until normal operating temperature is reached, or apply the specified humidity preconditioning treatment.
- Place the equipment on an insulating surface and connect it to the measurement circuit through an isolation transformer at the specified test voltage (for household appliances, 1.06 times the rated voltage; for medical equipment, 110 percent of rated supply voltage).
- Apply metallic foil to accessible non-conductive surfaces where the standard requires it, so that insulated enclosures are treated as conductive accessible parts.
- Connect the measuring network between the accessible parts and earth (for Class I equipment), or between accessible parts and each supply pole (for Class II equipment).
- Record the maximum indicated value during operation, including any switch-on transients where the standard requires it.
- Repeat the measurement with the supply polarity reversed, and under single-fault conditions such as an open neutral conductor; for medical devices, measure across all applicable fault combinations defined in IEC 60601-1.
- Compare the highest recorded value with the limit table of the applicable product standard.
Typical Acceptance Limits
- IEC 60335-1 (household appliances): 0.25 mA for Class II appliances, 0.5 mA for Class 0 and 0I appliances, 0.75 mA for Class I portable appliances, and 3.5 mA for Class I stationary motor-operated appliances; stationary heating appliances may be limited to 0.75 mA per kilowatt of rated input, subject to a defined maximum.
- IEC 62368-1 (ICT and AV equipment): touch current limits are typically 0.5 mA for ordinary persons under normal conditions, with higher values permitted only under defined fault conditions or for let-go-based classifications.
- IEC 60601-1 (medical devices): earth leakage current limits of 5 mA in normal condition and 10 mA in single-fault condition; enclosure leakage current of 100 microamperes normal and 500 microamperes single-fault; patient leakage current for CF applied parts limited to 10 microamperes in normal condition and 50 microamperes in single-fault condition.
All measurements should be performed by accredited third-party laboratories or properly trained in-house personnel using calibrated instruments, since measurement circuit grounding, transformer isolation, and network selection directly influence the result.
Applications
- Certification and market access: demonstrating compliance for CB Scheme, CE marking, UL listing, and CCC marking submissions
- Product safety design validation: verifying insulation systems, EMI filter layouts, and creepage and clearance decisions during development
- Production line routine testing: end-of-line leakage checks required by standards such as IEC 60601-1 for medical devices
- Periodic inspection and field safety verification of installed equipment and medical systems
- Insulation aging and reliability research, including humidity, temperature, and long-term stress studies
- Root-cause analysis of residual current device tripping, insulation degradation, and shock incident investigations
FAQ
What is the difference between leakage current and touch current?
Leakage current is the general term for unintended current escaping through insulation or filter components. Touch current is the specific portion of that current that would flow through a person touching accessible parts, measured through a standardized human body impedance network as defined in IEC 60990.
Can a standard multimeter be used to measure leakage current?
No. A multimeter does not reproduce the frequency-weighted human body impedance network, so its readings are not compliant with IEC 60990-based methods. A dedicated leakage current tester or calibrated measuring device must be used.
Why must the supply polarity be reversed during testing?
Reversal of the line and neutral connections is a single-fault condition that can significantly change capacitive leakage paths. Standards require measurement in both polarities to identify the worst case.
At what voltage is leakage current measured?
Most standards specify measurement at 1.06 to 1.10 times the rated supply voltage to account for normal grid voltage tolerance, with the equipment operating under normal or specified load conditions.
How is leakage current measured on Class II (double-insulated) products?
For Class II products there is no protective earth, so the current is measured between accessible parts (including metallic foil applied to non-conductive enclosures) and each supply pole in turn, with limits typically 0.25 mA for household appliances.