075582814553
In power electronics, insufficient spacing between conductive parts can cause air arcing or surface tracking. Creepage and clearance define two different insulation paths and are essential for safe, reliable, and standards-compliant equipment. Understanding creepage distance, clearance distance, and the factors behind their requirements is an important part of power electronic design.
Figure 1. Creepage vs. Clearance
Creepage and clearance describe the minimum distances between conductive parts that have a significant voltage difference. Both are important in insulation design, but the measurement path is different.
Clearance is the shortest distance between two conductive parts measured through air. For example, when high-voltage and low-voltage conductors are separated by an open space, the shortest path directly through the air between them is the clearance distance. It is mainly related to the ability of the air gap to withstand electrical stress without breakdown or arcing. Clearance is particularly important when a circuit may experience transient overvoltages. A power supply, inverter, or converter may operate at a fixed voltage during normal operation but experience much higher transient voltages during switching or other abnormal events. The clearance, therefore, cannot always be determined from the nominal operating voltage alone.
Creepage is the shortest distance between two conductive parts measured along the surface of a solid insulating material. Unlike clearance, the path follows the surface of the PCB, package, connector, or other insulating structure. Surface contamination and moisture can reduce the insulation performance of that path and increase the risk of electrical tracking. Thus, material properties heavily influence creepage calculations. A material's Comparative Tracking Index (CTI), combined with the pollution degree of the operating environment, establishes the minimum required surface path.
The difference can be summarized as follows:
| Parameter | Creepage | Clearance |
| Measurement path | Along an insulating surface | Through air |
| Main concern | Surface tracking and contamination | Air breakdown and arcing |
| Key factors | Working voltage, pollution degree, material group/CTI | Impulse voltage, overvoltage conditions, altitude |
| Typical locations | PCB surface, package surface, connectors | Air gaps between conductive parts |
In many practical designs, the required creepage distance is greater than the clearance. However, this is not a rule that applies to every design. The required values depend on the applicable standard and the actual electrical and environmental conditions.
The purpose of creepage and clearance is to maintain the required level of insulation between conductive parts under normal operating conditions and specified abnormal or transient conditions. Insufficient clearance can allow an excessive voltage to break down the air gap and create an arc. Once an arc forms, it can damage insulation, nearby components, or conductive structures. Insufficient creepage can create a path for surface tracking, especially when the insulating surface is exposed to moisture or contamination. Over time, electrical stress can contribute to surface degradation and the formation of a more conductive path.
These requirements are particularly important when a design contains different voltage domains, such as the primary and secondary sides of an isolated power supply, a high-voltage DC bus and a low-voltage control circuit, or an isolated gate driver connected between high- and low-voltage sections. Creepage and clearance are not arbitrary layout rules; they form the foundation of insulation coordination under IEC 60664-1, balancing working voltages, overvoltage categories, contamination, and material limits.
Working voltage is the voltage that an insulation system is subjected to during normal operation. It is one of the main parameters used to determine creepage and clearance requirements. For example, an isolated power converter may have a high-voltage input section and a low-voltage output section. The relevant working voltage is the voltage stress across the insulation barrier, not simply the nominal voltage printed on the product label.
For AC systems, the applicable RMS and peak values may both be relevant depending on the standard and the particular insulation requirement. For DC systems, the actual continuous voltage across the insulation must be considered.
Waveform and frequency can also matter. IEC 60664-1 covers equipment with frequencies up to 30 kHz. Where insulation is subjected to higher-frequency voltage stress, IEC 60664-4 provides additional considerations for clearances, creepage distances, and solid insulation.
Power electronic circuits can experience short-duration voltage spikes from switching events and supply disturbances. For this reason, the clearance requirement is closely associated with transient overvoltage and rated impulse voltage. The relevant overvoltage category, impulse voltage, and insulation type should be established before selecting the required clearance distance. A generic clearance chart based only on nominal voltage may therefore give an incomplete result.
The surrounding environment affects the performance of an insulating surface. Dust, moisture, salts, and other contaminants can make the surface more conductive and increase the risk of tracking.
IEC 60664-1 classifies operating environments using Pollution Degree (PD). In broad terms:
• Pollution Degree 1: No pollution or only dry, non-conductive pollution.
• Pollution Degree 2: Normally non-conductive pollution, with temporary conductivity possible because of condensation.
• Pollution Degree 3: Conductive pollution or dry pollution that can become conductive because of condensation.
• Pollution Degree 4: Persistent conductive pollution, including conditions involving sustained moisture.
The correct pollution degree should reflect the equipment's actual operating environment. Because contamination mainly affects the behavior of an insulating surface, it is an important factor when determining creepage distance.
Comparative Tracking Index (CTI) indicates an insulating material's resistance to surface tracking. Higher CTI generally means better tracking resistance.
IEC 60664-1 classifies materials into groups according to CTI:
| Material Group | CTI |
| Group I | CTI ≥ 600 V |
| Group II | 400 V ≤ CTI < 600 V |
| Group IIIa | 175 V ≤ CTI < 400 V |
| Group IIIb | 100 V ≤ CTI < 175 V |
Higher CTI materials resist tracking far better, allowing shorter creepage distances. FR-4 is a material family rather than a single CTI classification. Use the laminate manufacturer’s IEC 60112 test data or certification. Material Group IIIa covers 175 ≤ CTI < 400, do not assign every FR-4 laminate a fixed CTI of 175–225.
Figure 2. IEC 60112 CTI Test Concept and Surface-Tracking Process
Clearance depends directly on atmospheric pressure. At altitudes above 2,000 meters, air density drops, lowering its breakdown voltage (Paschen’s Law). Clearance values designed for sea level must be multiplied by altitude correction factors (per IEC 60664-1) for equipment installed in high-altitude solar farms, aerospace systems, or mountainous regions.
Figure 3. Altitude correction factor for clearance distance per IEC 60664-1
The required distance also depends on the type of insulation being provided. Common categories include:
• Functional insulation: insulation required for the circuit to operate correctly but not intended to provide protection against electric shock.
• Basic insulation: insulation that provides basic protection against electric shock.
• Supplementary insulation: independent insulation added to basic insulation to reduce the risk of electric shock if the basic insulation fails.
• Reinforced insulation: a single insulation system designed to provide protection equivalent to double insulation.
The insulation type matters because the same working voltage may require different spacing depending on the level of protection required.
This is one reason that a single “recommended spacing” cannot be applied to every high-voltage design.
A reliable design process starts with the applicable product standard rather than with a generic spacing table.
IEC 60664-1 is a fundamental reference for insulation coordination in low-voltage systems. The applicable product safety standard takes precedence and may modify or add requirements. The current consolidated edition is IEC 60664-1:2020+AMD1:2025, covering equipment with rated voltages up to 1,000 V AC or 1,500 V DC and frequencies up to 30 kHz.
For power electronic equipment, other product or group safety standards may apply depending on the application. Examples include:
| Standard | Typical Scope |
| IEC 60664-1 | General insulation coordination for low-voltage equipment |
| IEC 62477-1 | Safety requirements for power electronic converter systems and equipment |
| IEC 62368-1 | Audio/video and information and communication technology equipment |
| IEC 61800-5-1 | Adjustable-speed electrical power drive systems |
| IEC 60664-3 | Coating, potting, and moulding used for protection against pollution |
IEC 62477-1 specifically covers power electronic converter systems and equipment and can also serve as a reference for product standards covering applications such as drives, UPS systems, and low-voltage DC power supplies.
IEC 62368-1 is a product safety standard for audio/video and information and communication technology equipment, while IEC 61800-5-1 covers adjustable-speed electrical power drive systems.
The correct standard should therefore be identified before selecting the final creepage and clearance values.
Identify the applicable product standard → classify the insulation → determine the working voltage and rated impulse voltage → assign the pollution degree and material group → obtain the required distances from the applicable tables → apply the altitude correction to clearance → verify the final PCB geometry and manufacturing tolerances.
Once the applicable standard is known, collect the conditions that affect the insulation requirement:
• Maximum working voltage
• AC or DC operating conditions
• Transient overvoltage and rated impulse voltage
• Overvoltage category
• Pollution degree
• Material group or CTI
• Insulation type
• Maximum operating altitude
• Relevant frequency or waveform conditions
These parameters form the basis for selecting the required creepage and clearance distances.
Creepage is generally determined from the working voltage, pollution degree, material group, and insulation type, following the applicable standard. The basic principle is straightforward: a higher voltage generally creates greater insulation stress, while a more polluted environment or a material with lower tracking resistance may require a longer surface path. The final value should be taken from the appropriate table or calculation method in the applicable standard rather than from a general-purpose online chart. IEC 60664-1 includes dedicated procedures for determining creepage distances.
Clearance is determined primarily by the voltage stress that the air gap must withstand. The process generally involves determining the applicable rated impulse voltage, insulation type, and other system conditions before selecting the corresponding minimum air distance. Altitude correction may then be required for installations above the standard reference altitude. Because clearance is associated with air breakdown, it should always be checked against the shortest actual air path in the physical construction. A visually large gap does not necessarily represent the true clearance if another part of the geometry creates a shorter path.
The design should be checked as a complete insulation system rather than by looking at one pair of PCB traces in isolation. For example, verification may need to include:
• PCB traces and copper areas
• Component pins and pads
• Connector terminals
• Transformer and relay structures
• Isolation-device packages
• Slots, cutouts, and other PCB features
• Enclosures or accessible conductive parts
The shortest relevant path is what matters. Component manufacturers often specify package-level creepage and clearance separately, and those values do not automatically guarantee that the surrounding PCB layout meets the requirements.
Creepage and clearance appear in many types of power electronic equipment. The exact requirements depend on the applicable standard and system conditions, but several common insulation challenges can be identified.
In an isolated AC/DC power supply, the primary side can operate at hazardous mains voltage while the secondary side may provide a much lower output voltage. The isolation barrier between these two domains therefore needs to be evaluated for the appropriate insulation type, working voltage, transient conditions, pollution degree, and material characteristics. The transformer, PCB, optocoupler or digital isolator, connectors, and other components can all contribute to the overall insulation system.
Isolated DC/DC converters also require controlled spacing between input and output domains. This is common in industrial power supplies, battery systems, telecom equipment, and isolated control circuits. The required spacing depends on the voltage difference across the isolation barrier and the applicable safety requirements.
Motor drives and inverters can contain high-voltage DC buses, switching nodes, and motor-side outputs. These circuits can experience significant transient voltage stress in addition to their normal operating voltage. For adjustable-speed electrical power drive systems, IEC 61800-5-1 provides application-specific safety requirements covering electrical, thermal, fire, mechanical, and energy hazards.
Solar inverters combine relatively high DC voltages on the PV side with AC grid interfaces and low-voltage control electronics. The equipment may also be installed outdoors or at elevated locations. As a result, the insulation design has to account for both electrical stress and environmental conditions. The applicable product standard should be identified before determining the final spacing requirements.
Electric vehicles, battery energy storage systems, onboard chargers, and related power converters can contain high-voltage battery circuits alongside low-voltage control and communication circuits. As system voltages increase, the insulation barrier becomes increasingly important. At the same time, the final creepage and clearance requirements depend on the particular equipment, insulation system, environment, and applicable automotive or product standard rather than on battery voltage alone.
Mistake 1: Looking Only at Nominal Voltage
A common shortcut is to take a nominal system voltage and immediately select a spacing value. This approach can miss important factors such as transient overvoltage, overvoltage category, insulation type, pollution degree, and altitude. The correct value must be derived from the complete insulation-coordination conditions.
Mistake 2: Confusing Creepage With Clearance
A 5 mm spacing on a PCB does not automatically mean that both creepage and clearance are 5 mm. Clearance follows the shortest path through air, while creepage follows the shortest path across an insulating surface. The two paths can be different because of PCB geometry, package shape, slots, or other structures.
Mistake 3: Ignoring the PCB Material
The package of an isolation component may have a high CTI and a corresponding creepage rating, but the PCB around it may use a different material group. If the PCB becomes the limiting insulation surface, the component's own creepage specification may not be enough to demonstrate compliance.
Mistake 4: Measuring Only the Obvious Trace-to-Trace Gap
The shortest path may occur around the side of a component or between pads, pins, vias, or other conductive structures. For this reason, clearance and creepage should be checked across the actual physical geometry rather than by measuring only the most obvious pair of traces. TI's design guidance shows that package geometry can make the shortest creepage path different from the path a designer might expect.
Figure 4. How a Qualifying PCB Slot Can Increase the Creepage Path
Mistake 5: Assuming Conformal Coating Automatically Solves the Problem
Coating can provide protection against pollution under the conditions specified by the applicable standard, but it should not simply be treated as a universal replacement for spacing. IEC 60664-3 specifically covers assemblies protected by coating, potting, or moulding and defines requirements and test procedures for these methods. Any reduction in creepage or clearance must therefore be supported by the applicable insulation design method and verification process.
Mistake 6: Using a Generic Creepage and Clearance Table Without Checking the Standard
Online calculators and generic design charts can be useful for preliminary estimates, but they should not replace the applicable product standard. A power converter, motor drive, and ICT power supply may be subject to different standards and different evaluation methods. The final design should always be checked against the requirements applicable to the finished equipment.
Creepage and clearance are essential parts of insulation design. Clearance is measured through air, while creepage follows an insulating surface. Their required values depend on working voltage, transient overvoltage, pollution degree, material group, insulation type, and altitude.
Engineers should identify the applicable standard, determine the insulation conditions, and verify the shortest paths across the complete physical design.
Catalogue
FPGA / CPLD
Memory
MOS 
MCU 
DSP
OCEP
Secondary 
Other