New Energy Vehicle Leakage Current Testing: Standards, Methods, and Compliance Requirements

Leakage current testing is an essential electrical safety evaluation for new energy vehicles (NEVs), verifying that high-voltage battery systems, on-board chargers, inverters, and charging interfaces do not expose drivers, passengers, or service personnel to hazardous electric shock. By measuring touch current, protective conductor current, and insulation performance against standards such as GB 18384, ISO 6469, and IEC 61851, manufacturers can demonstrate regulatory compliance and safe operation under normal, fault, and environmental stress conditions. This article provides a comprehensive overview of the samples, test items, methodologies, and applications involved in professional leakage current testing for electric and hybrid vehicles.

Technical Overview

Leakage current in a new energy vehicle (NEV) refers to any unintended electrical current that flows from the high-voltage (HV) system to accessible conductive parts, the vehicle chassis, or protective earth. Because modern battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell electric vehicles (FCEVs) operate with voltage class B systems, typically 200 V to 900 V DC with AC traction circuits up to several hundred volts, even a small degradation of insulation can create a serious electric shock hazard for occupants, maintenance personnel, and charging users.

Leakage current testing therefore forms part of the mandatory electrical safety verification required by the major standards frameworks, including GB 18384-2020 (safety requirements for electrically propelled road vehicles), the ISO 6469 series (electrically propelled road vehicles, safety specifications), GB/T 18487.1 and IEC 61851-1 (conductive charging systems), GB 38031-2020 (safety requirements for traction batteries), and IEC 60990 (methods of measurement of touch current and protective conductor current). Together these standards define voltage class boundaries, current thresholds, insulation resistance limits, and the standardized measurement circuits used to evaluate them.

• Voltage class A: systems below 30 V AC RMS or 60 V DC, generally regarded as low risk.
• Voltage class B: systems above the class A limits; all HV traction and charging circuits in NEVs fall into this category and require rigorous leakage control.
• Commonly applied acceptance criteria include touch current limits of 3.5 mA AC RMS and approximately 1.5 to 2 mA DC at accessible parts, together with minimum insulation resistance of 500 ohms per volt for AC buses and 100 ohms per volt for DC buses.
• During AC charging, residual current protection is normally rated at 30 mA AC, and DC fast-charging systems must additionally detect smooth DC residual current from 6 mA upward, in accordance with IEC 61851-23 and GB/T 18487.1.

It is important to distinguish leakage current from related but different measurements. Insulation resistance quantifies the ohmic isolation between live parts and the chassis, whereas leakage current describes the total current, resistive plus capacitive, that actually flows under operating conditions, including contributions from Y-capacitors and EMI filter networks common in inverters and on-board chargers. Most NEVs also incorporate an on-board insulation monitoring device (IMD) that continuously tracks isolation, and laboratory leakage testing is used to validate the thresholds and response of this device under worst-case conditions.

Testing Samples

Leakage current and associated insulation evaluations can be performed at component, subsystem, and complete-vehicle level. Typical sample categories submitted to accredited third-party laboratories include the following.

High-Voltage Battery Packs and Battery Management Systems

Traction battery systems are tested for insulation resistance between the HV bus, with positive and negative terminals shorted together, and the enclosure or chassis. Measurements are performed in the as-received state and repeated after environmental conditioning such as damp heat, thermal cycling, vibration, and external short-circuit testing described in GB 38031-2020 and the GB/T 31467 series.

On-Board Chargers and DC/DC Converters

On-board chargers (OBCs) connect the vehicle directly to the external AC grid, making them a primary leakage path. Tests cover touch current at accessible parts, protective conductor current in the earth line, and behavior under single-fault conditions. High-voltage to low-voltage DC/DC converters are similarly evaluated because their galvanic isolation barriers separate the traction battery from the 12 V or 24 V vehicle electrical network.

Inverters, Motor Controllers, and Electric Drive Units

Power electronics generate high-frequency PWM output voltages that drive capacitive common-mode leakage through motor windings, cable capacitance, and EMI filters. Integrated electric drive assemblies are tested for leakage at rated load, at standstill, and under fault conditions to confirm compliance with ISO 6469-3 and GB 18384-2020.

High-Voltage Cables, Connectors, and Charging Couplers

HV wiring harnesses, connectors, and vehicle inlets conforming to GB/T 20234 and IEC 62196 are subjected to damp heat, water immersion, and IP ingress testing, after which leakage current and insulation measurements are repeated to verify that sealing performance prevents conductive leakage paths.

Auxiliary High-Voltage Components

PTC cabin heaters, electric air-conditioning compressors, high-voltage power distribution units (PDU), and electric power steering systems all operate at traction voltage, and each requires individual leakage and insulation verification before integration.

Complete Vehicles

Whole-vehicle testing verifies the interaction of all HV components with the chassis and body, including measurements between exposed conductive parts during charging modes and driving states, as well as post-crash electrical safety assessment at the end of the vehicle development cycle.

Testing Items

A professional leakage current evaluation program for new energy vehicles typically includes the following test items.

• Touch current at accessible parts under normal operating conditions, single-fault conditions, and wet or humid environments.
• Protective conductor current (earth leakage) for class I components with protective earthing.
• DC leakage current between the HV bus and the chassis, including verification of loss-of-isolation detection.
• AC leakage current, including high-frequency components attributable to switching converters and EMI filter Y-capacitors.
• Insulation resistance measurement of AC and DC buses against the chassis, using a 500 V or 1000 V DC test source selected according to the maximum working voltage.
• Residual current compatibility during AC charging (30 mA RCD behavior) and smooth DC residual current detection from 6 mA during DC fast charging.
• Leakage verification after environmental conditioning, including damp heat (IEC 60068-2-78), temperature cycling, salt spray, vibration, and IP water and dust exposure per ISO 20653 and IEC 60529.
• Post-crash leakage current, touch current, and insulation resistance verification following impact tests, in accordance with ISO 6469-4 and GB/T 31498.

Testing Methods

Touch Current Measurement Using the IEC 60990 Network

Touch current is measured with the standardized measuring device (MD) defined in IEC 60990, which simulates the frequency-dependent impedance of the human body. The measurement is made between each accessible conductive part and protective earth while the equipment operates at its maximum rated supply voltage, commonly specified as 106 to 110 percent of nominal in product standards. The test is first performed under normal conditions and then repeated with single faults applied, such as interruption of the protective conductor.

Protective Conductor Current Testing

For earthed components such as on-board chargers, the current flowing in the protective earth conductor is measured under normal and fault conditions to verify that it remains within the limits required by the applicable product safety standard.

Insulation Resistance Verification

A DC test voltage, typically 500 V or 1000 V depending on the maximum working voltage, is applied between the interconnected HV conductors and the chassis or accessible conductive parts. The measured resistance is compared against the 500 ohms per volt AC and 100 ohms per volt DC requirements of GB 18384-2020 and ISO 6469-3. For AC circuits, the static measurement is often supplemented with operating-condition tests because capacitive reactance can mask resistive leakage paths.

Environmental and Fault Condition Sequences

Leakage current is not constant; it deteriorates with humidity, contamination, temperature, and aging. Samples are therefore conditioned in climatic chambers, for example 48 hours or more of damp heat at elevated relative humidity, before measurements are repeated. Fault injection, such as opening the earth connection or bridging a single insulation barrier, confirms that protective measures keep the current within safe limits under failure conditions.

Whole-Vehicle and Charging-Mode Assessment

At vehicle level, measurements are taken between exposed conductive parts such as body panels, charging ports, and door handles and the wheels or external earth, in charging modes 1 through 4 and in the driving-ready state. Post-crash evaluations repeat the same measurements after barrier impact tests to confirm that insulation performance and leakage limits are maintained even after a collision.

Applications

Leakage current testing results are used throughout the entire new energy vehicle lifecycle.

• Type approval and market access, including compulsory certification in China and homologation against international regulations for export markets.
• Design verification (DV) and production validation (PV) programs during vehicle and component development.
• Production quality control, including end-of-line insulation and leakage checks on HV components.
• Charging interoperability assessment between vehicles, AC charging stations, and DC fast chargers.
• Reliability and aging studies, such as verification after thermal cycling, humidity exposure, and long-term durability testing.
• Post-accident safety investigations and regulatory or insurance assessments of crashed electric vehicles.

FAQ

What is the difference between leakage current and insulation resistance testing?

Insulation resistance measures the ohmic isolation between live parts and the chassis using an applied DC voltage, while leakage current measures the actual current, including both resistive and capacitive components, that flows under real operating conditions. Both are required: a system can pass a static insulation test yet still exhibit excessive capacitive leakage at high PWM switching frequencies.

What limits apply to touch current in new energy vehicles?

Commonly applied limits are 3.5 mA AC RMS and approximately 1.5 to 2 mA DC at accessible parts, under both normal and single-fault conditions, evaluated with the IEC 60990 measurement network. Insulation requirements are typically at least 500 ohms per volt for AC buses and 100 ohms per volt for DC buses in accordance with GB 18384-2020 and ISO 6469-3.

Which standards govern NEV leakage current testing?

The principal references are GB 18384-2020, the ISO 6469 series, GB 38031-2020, GB/T 18487.1, the IEC 61851 series, IEC 60990, and the GB/T 20234 and IEC 62196 coupler standards. Relevant international homologation regulations for export markets build directly upon these technical requirements.

Why must leakage tests be performed after humidity and environmental conditioning?

Moisture, condensation, salt contamination, and thermal cycling significantly reduce surface insulation resistance and can open leakage paths that do not exist in a dry laboratory state. Standards therefore require measurements in the worst-case conditioned state in order to reflect real-world service conditions.

Can testing be performed on complete vehicles or only on components?

Both. Component-level testing supports design validation and batch quality control, while complete-vehicle testing, including charging-mode and post-crash assessments, is necessary for type approval because it confirms the integrated behavior of all HV subsystems with the chassis and body.

What equipment is required for leakage current testing?

Testing requires calibrated AC/DC leakage or touch current meters compliant with IEC 60990, insulation testers with selectable 500 V and 1000 V outputs, climatic and humidity chambers, programmable AC and DC power sources capable of reproducing the traction voltage, and fault-injection fixtures. Accredited third-party laboratories operate this equipment within quality management systems conforming to ISO/IEC 17025.