Leakage current testing is one of the most critical safety evaluations for electrical and electronic products, protecting users from electric shock hazards during normal operation and single-fault conditions. This article provides an in-depth analysis of the major international and national leakage current standards—including IEC 60990, IEC 60335-1, IEC 62368-1, IEC 60601-1, and their UL, EN, and GB counterparts—covering measurement principles, limit values, test methods, and practical compliance considerations. Whether you are a design engineer, quality manager, or compliance professional, this guide will help you understand how leakage current requirements differ across standards and how to apply them correctly.
Technical Overview
Leakage current refers to the current that flows unintentionally through or across the insulation of an electrical device, or through protective components such as electromagnetic interference (EMI) filter capacitors, when the equipment is energized. Although small in magnitude, leakage current can pose a serious electric shock risk to operators and patients, particularly in humid environments or when insulation degrades over time. For this reason, virtually every product safety standard framework—IEC, EN, UL, GB, and JIS—establishes quantitative limits and standardized measurement procedures for leakage current.
The fundamental measurement methodology is defined in IEC 60990, Methods of measurement of touch current and protective conductor current. This standard specifies the measuring networks (simulating human body impedance), test circuits, and fault conditions used across the product safety family of standards. IEC 60990 distinguishes between two principal quantities: touch current, which is the current flowing through a person touching accessible parts of the equipment, and protective conductor current, which is the current flowing in the protective earth conductor of Class I equipment.
Because leakage current acceptance criteria depend strongly on the product category, each standard family applies its own limits and measurement conditions:
- IEC 60335-1 / EN 60335-1 / GB 4706.1 — household and similar electrical appliances.
- IEC 62368-1 / EN 62368-1 / UL 62368-1 / GB 4943.1 — audio/video, information, and communication technology equipment (replacing the legacy IEC 60950-1 and IEC 60065 standards).
- IEC 60601-1 / EN 60601-1 / GB 9706.1 — medical electrical equipment, with the strictest limits due to direct patient contact.
- IEC 60598-1 / EN 60598-1 — luminaires and lighting equipment.
- IEC 61010-1 / EN 61010-1 — measurement, control, and laboratory equipment.
- IEC 62841-1 — motor-operated power tools.
- UL 101 and UL 1310 — North American leakage current and Class 2 power unit requirements.
A correct standards analysis therefore requires not only knowing the numeric limits, but also understanding which measurement network, supply condition (rated voltage or 110% of rated), temperature state, and single-fault scenarios apply under each standard.
Testing Samples
Household and Similar Electrical Appliances
Refrigerators, washing machines, air conditioners, electric kettles, microwave ovens, vacuum cleaners, and hair dryers are evaluated under IEC 60335-1 and its part 2 series. Leakage current tests are performed at operating temperature as well as after humidity conditioning for certain appliances, with limits differentiated by appliance class and portability.
IT, Audio/Video, and Communication Equipment
Computers, monitors, printers, routers, televisions, power adapters, and chargers fall under IEC 62368-1. This hazard-based standard evaluates touch current against energy source classes (ES1/ES2/ES3), taking into account voltage, frequency, capacitance discharge, and the wet or dry condition of the accessible surface.
Medical Electrical Equipment and Systems
Patient monitors, infusion pumps, electrosurgical units, and diagnostic imaging systems are assessed under IEC 60601-1. Because patients may be electrically vulnerable or have direct conductive contact with internal tissue, the standard defines additional categories such as patient leakage current, patient auxiliary current, and total patient leakage current in multiple fault scenarios.
Luminaires and Lighting Products
Fixed, portable, and embedded luminaires, including LED drivers and street lighting, are tested per IEC 60598-1, which addresses leakage current for Class I and Class II constructions under normal and abnormal operating conditions.
Power Tools and Laboratory Equipment
Electric drills, saws, and grinders are covered by IEC 62841-1, while oscilloscopes, power supplies, and analytical instruments for professional use follow IEC 61010-1. Both standards reference the IEC 60990 measuring network methodology.
Testing Items
Depending on the applicable standard and product construction, the following leakage current quantities are typically evaluated:
- Earth leakage current (protective conductor current): the current returning through the protective earth conductor of Class I equipment; critical for verifying the integrity of the grounding path.
- Touch current (enclosure leakage current): the current that would flow through a person in contact with accessible parts or between two accessible parts simultaneously.
- Patient leakage current: the current flowing from applied parts through the patient to earth, measured under normal and single-fault conditions in medical equipment.
- Patient auxiliary current: the current flowing between applied parts of a medical device through the patient under normal intended use.
- Leakage current under single-fault conditions: measurements repeated with faults such as open neutral conductor, reversed supply polarity, or interruption of the protective earth conductor.
- DC leakage component: required by some medical and IT standards where direct current effects on tissue must be evaluated.
Testing Methods
Measuring Networks per IEC 60990
Leakage current is not measured with a simple ammeter. IEC 60990 specifies artificial impedance networks that simulate the frequency-dependent electrical response of the human body:
- Perception/reaction network: weights current components according to human perception thresholds, used for most touch current measurements in IT and AV standards.
- Let-go network: reflects muscle reaction (let-go) thresholds, historically used in IEC 60950-1 derived evaluations.
- Burn network: applies to high-frequency or high-capacitance circuits where tissue heating rather than shock is the dominant hazard.
Test Conditions and Configurations
General practice across the standards includes the following:
- Testing at rated supply voltage and frequency; many standards (such as IEC 60335-1 and IEC 60601-1) additionally require measurement at 110% of rated supply voltage to simulate high line conditions.
- Use of an isolation transformer and switchable polarity to allow reversal of the supply connections (line-neutral swap) as a single-fault condition.
- Opening of the neutral conductor while the protective earth remains connected, and interruption of the protective earth conductor for touch current measurement.
- Measurement both in the cold state and at operating temperature, since heating changes insulation properties and filter capacitor behavior.
- Humidity conditioning (typically 48 hours at approximately 91–93% relative humidity) required by appliance and medical standards before re-testing.
Representative Limit Values
The following typical limits illustrate how requirements differ by standard family; the applicable edition of the standard always governs:
- IEC 60335-1 (appliances): Class II — 0.25 mA; Class 0, 0I, and III — 0.5 mA; Class I portable — 0.75 mA; Class I stationary motor-operated — 3.5 mA; Class I stationary heating appliances — 0.75 mA per kW of rated input, up to a maximum of 5 mA.
- IEC 62368-1 (IT/AV): touch current classified against energy source levels, with ES1 boundaries around 0.5 mA (RMS, weighted) at power frequencies for ordinary conditions.
- IEC 60601-1 (medical): earth leakage current typically 5 mA normal / 10 mA single fault; touch current 100 microamps normal / 500 microamps single fault; patient leakage current 100 microamps normal / 500 microamps single fault for typical applied parts.
- Legacy IEC 60950-1 (IT equipment): handheld Class I — 0.75 mA; movable and stationary Class I — 3.5 mA (higher for permanently connected equipment); Class II — 0.25 mA.
- IEC 61010-1 (laboratory equipment): 0.5 mA under normal conditions, with higher values permitted under single-fault conditions for stationary equipment.
Applications
Leakage current testing serves multiple purposes across the product life cycle:
- Certification and market access: demonstrating compliance with leakage current limits is mandatory for CE marking under the Low Voltage Directive, CCC marking under GB standards, UL certification for North America, and PSE approval in Japan.
- Production line safety testing: manufacturers perform 100% routine leakage or touch current tests on finished units using calibrated production safety testers before shipment.
- Design verification and R&D: engineers use leakage current analysis during development to optimize EMI filter design, Y-capacitor selection, and grounding architecture without exceeding touch current limits.
- Comparative standards analysis for global products: products sold worldwide are evaluated against multiple standards, and the most stringent applicable limit usually drives the design envelope.
- In-service and periodic inspection: hospitals, factories, and laboratories verify leakage current during scheduled maintenance of medical devices, machine tools, and IT infrastructure to confirm continued safety.
Accredited third-party laboratories routinely perform these evaluations, providing test reports that support regulatory submissions, retailer requirements, and factory audits.
FAQ
What is the difference between leakage current, touch current, and protective conductor current?
Leakage current is the umbrella term. Protective conductor current (earth leakage current) flows in the protective earth wire of Class I equipment and is measured with the conductor intact. Touch current is the simulated current through a person contacting accessible parts, measured with the protective conductor interrupted. Modern IEC standards have largely adopted the touch current concept because it more accurately reflects the actual shock hazard to the user.
Why do leakage current limits differ so much between standards?
Limits depend on the user population and exposure scenario. Household appliance users include children and untrained persons, so portable Class I limits are strict at 0.75 mA. Medical patients may have compromised skin barriers or internal conductive connections, requiring limits as low as 10–100 microamps. Stationary industrial equipment with permanent wiring tolerates higher protective conductor currents because accidental contact probability and fault energy are managed differently.
Why is leakage current tested at 110% of rated voltage?
Utility supply voltage can rise above nominal values. Because leakage current through EMI filter Y-capacitors and insulation is roughly proportional to supply voltage, testing at 110% ensures the equipment remains safe under worst-case high-line conditions.
What equipment is required for leakage current testing?
A calibrated leakage current tester or safety analyzer incorporating the IEC 60990 measuring networks, an adjustable isolated AC power source with polarity reversal, and appropriate test probes or contact foils for accessible surfaces. Medical testing additionally requires patient simulating circuits defined in IEC 60601-1.
How can designers reduce leakage current?
Common strategies include reducing Y-capacitor values in the EMI filter, improving insulation spacing and material quality, adding internal shields connected to a grounded point, splitting filter capacitance, and ensuring clean, low-impedance protective earth bonding. Any reduction in filtering must be balanced against EMC performance requirements under CISPR or FCC emission limits.