How to measure leakage current
Accurate leakage current is vital for electrical safety. It ensures your device is safe for users and patients. Whether for medical or household use, you must choose the right leakage current measurement methods. This prevents shock hazards and ensures successful certification.
Incorrect methods can lead to dangerous errors. You might underestimate the current flowing through a human body. This article explains the networks, standards, and tools you need for compliance.
Methods & Instrumentation
In this article, we explore the fundamentals of measuring networks. You will understand standardized circuits from leading IEC standards, including IEC Guide 115, IEC 6990, and IEC 62353. instrumentation options will be discussed. We also discuss calibration and test setups. Finally will equip you with the knowledge to perform precise leakage current assessments in any professional context.
The Role of the Measuring Network
You cannot simply use a standard multimeter for these tests. You must use a “measuring network” or “body impedance model.” This artificial circuit simulates the electrical resistance of the human body. It allows us to measure the voltage drop and calculate the potential shock current.
Most compliance standards require specific network configurations to ensure consistency.
- Resistive Elements: These are typically around 1.5 kΩ to 2 kΩ. They simulate the internal resistance of the human body.
- Capacitive Elements: These mimic the capacitance of the skin. They also account for how impedance changes with frequency.
- Frequency Response: The network accounts for different risks. High frequencies cause burns, while low frequencies cause shocks.
These networks are essential. They ensure that your leakage current measurement methods yield results that reflect real-world safety risks.
Measuring Touch Current
There is no single way to achieve a correct leakage current measurement. The method depends on your device and the regulatory standard. Common standards include IEC 60990 or IEC 62353. Technicians generally rely on three primary techniques.y compliant leakage test, providing both reliability for engineers and confidence for regulators.
- IEC 62353 – Three methods for equipment and applied-part leakage, including direct and differential techniques
- IEC Guide 115 – Guidance on applying measurement uncertainty principles to conformity assessment
- IEC 6990 – Defines accuracy limits and component tolerances for leakage-current networks
The principal network types are:
- Protective-conductor (PE) network: Measures current flowing through the protective earth to verify grounding efficacy.
- Equipment-leakage direct method: Replicates the real leakage from live parts through the body-model network to earth (Class I/II).
- Applied-part leakage: Isolates leakage from patient-contacting parts to protective earth or secondary circuits. This one is the most used in product safety.
- Differential method: Calculates leakage by summing currents in all supply conductors and protective earth to zero, ideal for multi-wire systems.
Adhering to these network definitions is critical for certification under IEC and national standards. This ensures that your test results are both accurate and legally defensible.
Safety Leakage Current Measurement Instrumentation
Selecting the right leakage current measurement device is as important as the network itself. Instruments must accommodate the expected leakage-current range, waveform shape, and frequency content. Common options include:
- Leakage-current clamp meters with true-RMS capability, offering non-intrusive measurement on live conductors
- Dedicated leakage testers (e.g., Associated Research Omnia II or Compliance West LCB series) with built-in networks and pass/fail indicators
- Source-Measure Units (SMUs) and electrometers for high-resolution DC or low-frequency AC leakage below 10 nA
- Digital oscilloscopes paired with high-impedance probes to visualize transient or pulsed leakage currents
- RLC meters for verifying network components and ensuring capacitance and resistance values meet tolerance
A best practice is to choose instruments calibrated to a traceable standard, with known frequency response up to the highest test frequency. This reduces measurement uncertainty and helps to satisfy both IEC Guide 115 and ISO/IEC 17025 requirements.
Calibration & Frequency-Response Limits
All measuring networks and instruments degrade or drift over time. Regular calibration, including verification of component values and instrument response, is mandated to maintain traceability and uncertainty budgets. IEC 115 provides detailed guidance on evaluating uncertainty contributions from each component and connection. For example Compliance West reports that high-precision leakage-current boxes are accurate to ±5 % from 20 Hz to 1 MHz, reflecting common certification test frequency limits.
Key calibration considerations include:
- Frequency sweep verification to confirm network impedance matches the nominal curve up to 1 MHz.
- Temperature stability testing, ensuring component drift remains within tolerance over 0 °C–40 °C.
- Traceability to national calibration labs (e.g., NIST, PTB) for both resistance and capacitance standards.
- Periodic re-calibration intervals, typically 12 months, unless justified otherwise by uncertainty analysis.
By rigorously managing calibration, labs can reduce measurement uncertainty. This ensures it meets regulatory thresholds. Auditors will have confidence in the integrity of test data.
Test Procedure & Correct Setup
A robust test setup minimizes extraneous currents and ensures repeatable results. The typical configuration includes:
- Earth Reference
- Establish a low-impedance connection to building protective earth.
- Equipment Under Test (EUT) Placement
- Position the EUT on an insulating support, away from conductive surfaces.
- Network & Instrument Connection
- Connect the network’s live input to the mains or applied part, its neutral to the instrument’s current input, and its earth terminal to protective earth. Consider the use of an Insulation Transformer to improve accurancy.
- Shielding & Guarding
- Use a grounded Faraday cage or shielded room for sensitive measurements below 1 µA.
- Measurement Execution
- Apply the specified test voltage (e.g., 264 V AC), record RMS or peak currents, and compare against standard limits.
- Data Logging & Verification
- Capture the measurement waveform or value, and validate it against acceptance criteria in the test plan.
Following a standardized procedure is essential. Procedures like those in IEC 62353 Annex A or IEC 60601-1 clause 8 ensure that results are comparable across different labs. They also allow for consistency over time.
Key Takeaways
- Measuring networks simulate human-body or earth paths to create controlled test conditions essential for electrical safety and EMC certification.
- Standards like IEC 60990, IEC 62353, IEC Guide 115 define network topologies and accuracy limits to ensure global compliance.
- Instrumentation ranges from clamp meters to high-precision SMUs. Each tool must be selected based on current range, frequency content, and required traceability.
- Calibration and frequency-response verification are non-negotiable for maintaining low measurement uncertainty and meeting ISO/IEC 17025 or national accreditation requirements.
- A rigorous test setup—including earth reference, shielding, and data logging, ensures that your leakage-current measurements are both reliable and auditable.
By integrating robust networks, calibrated instruments, and standardized procedures, you can confidently demonstrate compliance with regulatory frameworks. This protects users, pets, and equipment alike.
More about leakage current measurement
In Part 1 of this series, you can find the background of fundamental theory of leakage current. It explains its significance for electrical safety. Topics covered include the physical transfer mechanisms (conductive, capacitive, and inductive). Key definitions and measurement circuits are also discussed. The series looks at human-body impedance models and physiological risks. This includes fibrillation and the role of frequency in both people and pets.
In Part 3, we shift to leakage current design and mitigation strategies to reduce it to a minimum. You’ll learn how to select and qualify insulation. You will also define creepage and clearance. Additionally, learn how to optimize PCB layouts and EMI/EMC filters. Each of these tasks is done with an eye toward electrical safety, regulatory compliance, and smooth certification. We’ll also cover grounding schemes and validation protocols to make sure your products stay safe and compliant throughout their lifecycle.
References & Further Reading
- IEC 60990:1999 – Methods of Measurement of Touch Current and Protective Conductor Current
- IEC 62353:2014 – Medical Electrical Equipment – Recurrent Test and Test After Repair of Medical Electrical Equipment
- IEC Guide 115 – Application of Measurement Uncertainty to Conformity Assessment Activities
- EBME. IEC 62353 Leakage Measurements
- Compliance West. Leakage Current Box Configurations. Product Page
- TDK Lambda. Understanding Leakage Currents in Medical Applications
- In compliance Magazine. Leakage Current Measuring Circuits
- Hipot testing test methods. How to perform Hipot Test
Frequently Asked Questions (FAQ)
Here are common questions technicians ask about leakage current measurement methods.
generally, no. A standard multimeter does not have the correct input impedance. It lacks the body impedance network required by safety standards. Using one will yield inaccurate results.
Earth leakage flows through the protective earth conductor. Enclosure leakage flows from the case of the device to the user. Enclosure leakage is critical if the ground connection fails.
Modern electronics use switching power supplies. These create complex, non-sinusoidal waveforms. An average-responding meter misses the peaks of these waveforms. High frequency reading instruments captures the full energy, resulting in a higher, more accurate reading.
