Digital computer leakage current testing measures the touch current and protective conductor current that desktops, laptops, servers, and their power supplies can deliver under normal and single-fault conditions, verifying compliance with international safety standards such as IEC 60950-1, IEC 62368-1, IEC 60990, and GB 4943.1. As a mandatory element of product safety evaluation for information technology equipment, this test confirms that accessible parts of the equipment remain within safe current limits that protect users from electric shock. Accredited third-party laboratories perform leakage current testing to support market access, certification schemes, and quality assurance for computer manufacturers worldwide.
Technical Overview
Leakage current in digital computers is the unintended electrical current that flows from live parts, through insulation or intentional electromagnetic interference (EMI) filter components, to accessible surfaces or to the protective earth conductor. In switching-mode power supplies used in virtually all digital computers, Y-class capacitors connected between the line, neutral, and earth conductors are the dominant source of leakage current, together with capacitive coupling across transformers and insulating barriers. While some leakage is unavoidable in filtered equipment design, excessive leakage can expose users to perceptible or even hazardous electric shock.
Safety standards distinguish two principal quantities. Touch current is the current that would flow through a person bridging an accessible part and earth (or another accessible part) when the impedance and frequency response of the human body are taken into account. Protective conductor current is the current flowing in the protective earth conductor of Class I equipment under normal operating conditions. Both are measured using standardized circuits and weighting networks defined in IEC 60990, which simulate human body impedance and frequency sensitivity.
The governing product standards for digital computers include IEC 60950-1 (the legacy safety standard for information technology equipment), IEC 62368-1 (the hazard-based successor standard covering audio/video, information and communication technology equipment), and the corresponding Chinese national standard GB 4943.1, whose 2022 edition is aligned with IEC 62368-1:2018. Regional adoptions such as EN 62368-1 in Europe, UL 62368-1 in North America, and JIS C 62368-1 in Japan reference the same measurement principles. Typical acceptance limits under IEC 60950-1 and GB 4943.1 are 0.25 mA for Class II equipment, 0.75 mA for general Class I equipment, and up to 3.5 mA for specific Class I configurations such as permanently connected or movable equipment rated above 150 V, provided appropriate marking and installation requirements are met. Under IEC 62368-1, touch current for ordinary persons in energy source class ES1 is limited to 0.5 mA a.c. r.m.s. under normal operating conditions.
Testing Samples
Desktop and Tower Computers
Complete desktop microcomputer systems with internal power supply units represent the most common test sample. The equipment under test is configured in its normal operating state, connected to a supply at rated voltage and frequency, with all simultaneously operable loads and peripherals energized as described in the manufacturer's installation instructions.
Notebook Computers and External Power Adapters
For portable and notebook computers, leakage current testing is primarily performed on the external AC adapter or power brick, since the adapter is the component directly connected to the mains supply. The computer itself is treated as the load, and measurements are taken with the adapter delivering its rated output. Both the adapter and the complete adapter-computer combination may be evaluated.
Servers, Workstations, and Industrial Computers
High-power servers, workstations, rack-mounted systems, and industrial computers with redundant or multiple power supplies are tested with all supplies installed and operational. Because these systems often employ large EMI filters, they are more likely to approach higher protective conductor current limits and may rely on provisions for permanently connected installation.
Computer Peripherals and Accessories
Monitors, docking stations, external storage enclosures, printers, and universal serial bus hubs that are powered from the mains fall within the same safety framework and are tested for leakage current using identical methods. Samples may include finished production units or engineering prototypes submitted for design verification and type testing.
Testing Items
The leakage current evaluation for digital computers typically encompasses the following measurement items:
- Touch current at accessible parts under normal operating conditions
- Touch current under single-fault conditions, including interruption of the protective earth conductor and interruption of the neutral supply conductor
- Touch current with both normal and reversed polarity of the mains supply connection
- Protective conductor current of Class I equipment under normal operating conditions
- Measurements performed at rated supply voltage and rated frequency, and, where required, at the upper and lower limits of the rated voltage range
- Evaluation at maximum steady-state load and, where applicable, under conditions producing the highest leakage, such as power-on inrush states identified during pre-investigation
Testing Methods
Test Circuit and Measuring Network
Leakage current is not measured with a simple ammeter because the human body responds to current in a frequency-dependent manner. Testing therefore employs the measuring networks specified in IEC 60990 and referenced by IEC 60950-1, IEC 62368-1, and GB 4943.1. These networks combine resistive and capacitive elements that weight the current across the relevant frequency spectrum, simulating human body impedance and converting the touch current into a proportional voltage that is read by a suitable measuring instrument. The equipment under test is supplied from an isolated, adjustable alternating current source capable of delivering the rated voltage at the rated frequency. A calibrated leakage current tester or safety analyzer incorporating the standard network, together with conductive probes or electrodes applied to accessible parts, completes the measurement setup.
Test Procedure
Testing is normally conducted in an ambient environment of 15 °C to 35 °C with relative humidity not exceeding 75 percent, and samples intended for type testing may first undergo humidity preconditioning as specified by the applicable standard. The general sequence is as follows:
- Configure the computer system in accordance with the manufacturer's operating instructions, with earthed parts, signal ports, and accessible surfaces identified and documented
- Connect the equipment under test to the isolated supply through the measuring network, ensuring reproducible probe contact with each accessible part selected for evaluation
- Energize the equipment at rated voltage and frequency and allow it to reach steady-state operating conditions
- Record the touch current for each accessible part under normal polarity and then repeat the measurement with reversed supply polarity
- Apply the prescribed single-fault conditions, such as opening the neutral conductor or, for touch current evaluation of Class I equipment, opening the protective earth conductor, and repeat the measurements
- Measure the protective conductor current of Class I equipment under normal operating conditions using the appropriate circuit defined in the standard
- Report the highest recorded values together with the test circuit configuration, supply conditions, and fault state for each measurement
Acceptance Criteria
Measured touch current and protective conductor current must not exceed the limits of the applicable standard. Under IEC 60950-1 and GB 4943.1, the commonly applied values are 0.25 mA for Class II equipment, 0.75 mA for Class I equipment in general configurations, and 3.5 mA for specific Class I equipment permitted to rely on higher limits, subject to marking and installation constraints. Under IEC 62368-1 and GB 4943.1-2022, touch current accessible to ordinary persons must remain within the ES1 limit of 0.5 mA a.c. r.m.s. in normal operating conditions, with defined allowances for abnormal and single-fault conditions. Protective conductor current for Class I equipment is generally limited to 5 mA unless the equipment is designed, marked, and installed for higher values. Any measured value exceeding the applicable limit constitutes a failure requiring design remediation, typically involving reduction of Y-capacitance, improved insulation arrangement, or revised earthing provisions.
Applications
Digital computer leakage current testing serves multiple purposes across the product lifecycle:
- Mandatory certification for market access, including the China Compulsory Certification scheme for information technology equipment under GB 4943.1, CE marking under the Low Voltage Directive with EN 62368-1, and national certifications built on IEC 62368-1 or UL 62368-1 requirements
- Participation in the IECEE Conformity Assessment Scheme for Electrotechnical Equipment and Components Certification Bodies (CB Scheme), where leakage current test results are included in the CB test report for international recognition
- Design verification during research and development, allowing engineering teams to validate power supply selection, EMI filter design, and insulation coordination before tooling and mass production
- Factory quality control and incoming inspection of power supply units, external adapters, and finished computer systems on production lines and in periodic surveillance testing
- Compliance evidence in procurement tenders, enterprise qualification programs, and regulatory investigations where demonstrable electrical safety data is required
FAQ
Q: What is leakage current in a digital computer?
A: It is the small current that flows from the mains supply through insulation and EMI filter components, mainly Y-capacitors in the power supply, to accessible parts or the protective earth conductor. It is inherent to filtered equipment but must be limited to protect users from electric shock.
Q: Which standards govern leakage current testing for digital computers?
A: The principal standards are IEC 60950-1 and its successor IEC 62368-1, the measurement methodology standard IEC 60990, and the Chinese national standard GB 4943.1, together with regional adoptions such as EN 62368-1, UL 62368-1, and JIS C 62368-1.
Q: What is the difference between touch current and protective conductor current?
A: Touch current is the current that would flow through a person contacting an accessible part, measured with a network simulating human body impedance. Protective conductor current is the current flowing in the earth wire of Class I equipment during normal operation.
Q: Why are tests performed under reversed polarity and single-fault conditions?
A: Reversed supply polarity and faults such as an open neutral or an interrupted protective earth conductor can significantly alter leakage current paths. Standards require these conditions to ensure the equipment remains safe even when the installation or supply is not ideal.
Q: What are the typical pass limits?
A: Under IEC 60950-1 and GB 4943.1, common limits are 0.25 mA for Class II equipment, 0.75 mA for Class I equipment, and 3.5 mA for specific permitted Class I configurations. Under IEC 62368-1, the ES1 touch current limit for ordinary persons is 0.5 mA a.c. r.m.s. in normal conditions.
Q: What samples should be submitted for testing?
A: Representative production units are preferred, including the complete computer with its power supply or external adapter, the operating instructions, and, where relevant, any accessories needed to reproduce normal operating conditions. Accredited third-party laboratories can advise on sample quantities for type testing and follow-up verification.