Handheld instruments
system from external surges or faults. The main hurdle is supplying power to components located on the isolated side.
5. PCB Layout Considerations
Proper PCB layout is a critical factor in ensuring medical devices meet the safety requirements outlined in IEC 60601-1, particularly regarding creepage and clearance distances. These distances are essential for preventing electrical shock and ensuring patient and operator safety. Illustrated in Figure 2, creepage refers to the shortest path between two conductive elements along the surface of an insulating material, while clearance is the shortest path through air. To comply with the standard, designers must carefully space high voltage traces away from low voltage traces, following specific guidelines based on working voltage and material group. Strategic use of slots and isolation barriers can effectively increase creepage distances without expanding the overall board size, which is especially useful in compact medical device designs. Additionally, selecting materials with appropriate comparative tracking index (CTI) ratings and considering environmental factors such as altitude and pollution degree are essential for accurate spacing. All layout decisions should be integrated into the device’s broader risk management strategy to ensure compliance under both normal and fault conditions, ultimately contributing to the safety and reliability of the medical device.
Leakage Current Management Under IEC 60601-1, controlled leakage current is essential for ensuring the safety and reliability of medical electrical equipment. Figure 3 shows the different leakage currents in medical devices. The standard defines various leakage currents - earth, touch, patient, and patient auxiliary - arising from insulation flaws or capacitive coupling. Leakage current refers to the unintended flow of electrical current through an abnormal or undesired path, often occurring when a device is powered off or when insulation fails. This phenomenon can happen in any electrical system and may lead to issues such as energy waste, circuit breaker trips, electrical noise, overvoltage, fire hazards, or even electric shock - especially if the current finds a path to ground through a human body. Common causes include poor insulation, grounding problems, environmental factors like temperature, and imperfections in electronic components. The standard mandates testing under normal and single fault conditions using a human body model to simulate realistic impedance and frequency responses. Strict leakage limits are set, especially for cardiac applications. In the context of IEC 60601-1 Type B, BF, and CF refer to classifications of applied parts - the components of a medical device that come into physical contact with the patient. These classifications are primarily
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Figure 2. Difference between creepage and clearance.
concerned with protection against electrical shock, and they differ based on the nature and location of patient contact.
Type B (body): Basic protection, grounded, no direct patient contact (for example, hospital beds).
Type BF (body floating): Enhanced insulation for conductive skin contact (for example, ultrasound probes).
Type CF (cardiac floating): Highest protection for direct heart contact (for example, pacemaker leads).
Designers can reduce leakage using low leakage components, optimised grounding, shielding, and filtering. Compliance is verified via rigorous testing, including IEC 62353 in service testing of medical electrical equipment for routine checks and fault simulations, ensuring safe operation for both patients and operators.
Testing and Validation
After completing the design of a medical electrical device, thorough testing is required to ensure compliance with IEC 60601-1 standards. This includes verifying safety under both normal and fault conditions through key electrical tests.
Dielectric strength testing checks insulation integrity by applying high voltages. Insulation resistance testing ensures isolated components prevent unintended current flow, while leakage current testing simulates fault scenarios to confirm leakage remains within safe limits. Creepage and clearance distances are assessed with stricter requirements for components interfacing with patients, and insulation must meet specific thickness and strength criteria - often requiring reinforced insulation for higher protection. Devices are also tested under single fault conditions, such as short or open circuits and environmental stress, to ensure continued safety. To maintain compliance through-out the device’s lifecycle, routine and post-repair testing is conducted, forming a comprehensive framework for safe and reliable operation.
ADI SOLUTIONS FOR MOP Isolated Power
ADI’s isolated power converters use transformer- based isolation instead of optocouplers. This provides better performance, longer life, and higher reliability. Many of these devices offer reinforced insulation, making them suitable for 2× MOPP applications. The ADuM5020 is a fully integrated isolated DC-to-DC converter with low electromagnetic interference. It supports high working voltage and is suitable for medical device applications.
Figure 3. Leakage current in medical devices. May 2026 Instrumentation Monthly
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