Leakage current testing is a critical electrical safety evaluation for information technology equipment, verifying that unwanted current flowing through insulation remains within safe limits under normal and single-fault conditions. This testing is mandated by international safety standards such as IEC 62368-1, IEC 60950-1, GB 4943.1, and EN 62368-1, and is essential for product certification, market access, and user protection. This article provides a comprehensive technical overview of leakage current testing principles, sample types, test items, measurement methods, and typical applications for IT equipment.
Technical Overview
Leakage current refers to the unintended electrical current that flows through or across the insulation of equipment when it is energized. In information technology equipment (ITE), leakage current originates primarily from capacitive coupling between live parts and accessible surfaces, EMI filter components connected to the protective earth, and imperfections in insulation materials. Although usually small in magnitude, excessive leakage current can cause electric shock to users or malfunction of residual current devices (RCDs) in the installation.
Modern safety standards distinguish between two principal quantities:
- Touch current – the current that would flow through a person or animal when touching accessible parts of the equipment, measured using a standardized human body impedance network.
- Protective conductor current (earth leakage current) – the current flowing in the protective earth conductor under normal operating conditions, which is critical for verifying that the protective grounding system remains effective.
The governing standards for information technology equipment safety include IEC 62368-1 and its regional adoptions such as EN 62368-1, UL 62368-1, and GB 4943.1. Legacy products may still be evaluated under IEC 60950-1 or GB 4943.1-2011. The measurement methodology itself is defined in IEC 60990, "Methods of measurement of touch-current and protective conductor current," which specifies the measuring networks, electrode configurations, and test circuit arrangements.
Typical acceptance limits under the legacy IEC 60950-1 framework include a touch current of 0.5 mA for Class I equipment and 0.25 mA for Class II equipment, while protective conductor current is limited to 0.75 mA for hand-held equipment, 3.5 mA for movable equipment, and up to 5% of rated input current for larger pluggable or permanently connected equipment. IEC 62368-1 expresses equivalent requirements through the classification of electrical energy sources (ES1/ES2/ES3), and accredited third-party laboratories apply the appropriate limits based on the standard edition and product configuration.
Testing Samples
Personal Computing Devices
Desktop computers, laptop computers, tablets, and workstations are routinely submitted for leakage current evaluation. These products incorporate switched-mode power supplies with input filters that contribute significantly to protective conductor current.
Display and Peripheral Equipment
Monitors, projectors, printers, scanners, multifunction peripherals, and external storage devices are tested to confirm that accessible surfaces and signal connectors do not deliver hazardous touch current.
Network and Communication Equipment
Routers, switches, modems, servers, and data center equipment often operate continuously and are frequently touched by operators. Telecommunication ports may also require evaluation where they become accessible conductive parts.
Power Conversion Equipment
External power adapters, chargers, inverters, and uninterruptible power supplies (UPS) represent a major category of ITE leakage current testing, since high-frequency conversion stages and Y-capacitors in EMI filters generate measurable leakage paths.
Testing Items
A complete leakage current evaluation program for information technology equipment typically includes the following items:
- Touch current measurement at accessible parts under normal operating conditions.
- Protective conductor current measurement in the protective earth lead under normal operating conditions.
- Touch current measurement under single fault conditions, including interruption of the protective earth conductor.
- Leakage current measurement under supply fault conditions, such as open neutral conductor and reversed supply polarity.
- Frequency-weighted and unweighted measurements using the appropriate IEC 60990 measuring networks, accounting for the physiological effect of high-frequency components.
- Verification of compliance with ES1 or ES2 classifications per IEC 62368-1 where applicable.
Testing Methods
Leakage current testing is performed in accordance with the measurement techniques specified in IEC 60990, applied within the framework of IEC 62368-1 or the applicable legacy standard. The general method involves the following steps:
- Test setup: The equipment under test (EUT) is placed on an insulation surface and supplied from an isolated power source at rated voltage and frequency. For fault-condition evaluations, the supply voltage is increased to 110% of the rated value.
- Measurement network: A measuring network simulating the impedance of the human body is connected between the accessible part and earth. For touch current, a conductive foil or defined probe electrode contacts each accessible surface. For protective conductor current, the ammeter or measuring network is inserted in series with the protective earth conductor.
- Measurement procedure: Current is measured with the supply polarity in both positions, and the higher of the two readings is recorded. Measurements are repeated for each accessible part and each applicable fault condition, including protective earth interruption and neutral conductor interruption.
- Fault application: Single faults are applied one at a time, and the equipment is operated under normal load conditions throughout the test to represent worst-case operation.
- Instrumentation: Calibrated leakage current testers, true RMS voltmeters, or oscilloscopes with the appropriate measurement network are used. Measurement uncertainty must be considered when comparing results against the limit values.
The recorded values are compared against the applicable limit from the relevant standard. A margin account for measurement uncertainty is recommended, and accredited third-party laboratories typically report both measured values and pass/fail determinations.
Applications
Leakage current test results support a wide range of engineering and compliance activities:
- Product safety certification for national and international market access, including CB Scheme conformity, CE marking under the Low Voltage Directive, and CCC certification for products sold in China under GB 4943.1.
- Design verification during product development, allowing engineers to optimize EMI filter topology, Y-capacitor selection, and insulation coordination before final certification.
- Production line safety testing as part of routine quality control, commonly implemented as 100% inspection or periodic sampling using production leakage testers.
- Regulatory compliance demonstration for market surveillance authorities, procurement specifications, and enterprise IT asset acceptance.
- Failure analysis and root cause investigation when field reports indicate nuisance RCD tripping or user-perceived tingling sensations.
FAQ
What is the difference between touch current and protective conductor current?
Touch current is the current that can flow through a person touching accessible parts of the equipment, while protective conductor current is the current flowing in the protective earth wire during normal operation. Touch current relates directly to the risk of electric shock, whereas protective conductor current determines whether the protective earthing system and upstream protective devices remain effective.
Which standard should my information technology equipment comply with?
New products are generally evaluated under IEC 62368-1, or its regional equivalents such as EN 62368-1, UL 62368-1, and GB 4943.1. Products certified under IEC 60950-1 may continue under that standard during the applicable transition period, depending on the target market. Accredited third-party laboratories can confirm the correct standard edition for a specific product and market.
Why is leakage current tested at 110% of rated voltage?
Measuring under single fault conditions at 110% of rated supply voltage represents a conservative worst case. Higher supply voltage increases capacitive leakage proportionally, ensuring that the evaluated margin protects users under realistic upper-limit mains conditions.
Why must supply polarity be reversed during testing?
Reversing the line and neutral connections changes which internal components are at elevated potential relative to earth. Some leakage paths only become significant with one polarity, so both orientations must be measured and the higher value used for compliance assessment.
What causes excessive leakage current in IT equipment, and how can it be reduced?
Common causes include oversized Y-capacitors in the EMI input filter, degraded insulation, and contamination on printed circuit boards near live parts. Remedies include optimizing filter component values, improving insulation coordination and creepage distances, and reviewing the protective earthing design so that leakage is safely returned to source.