Clearance And Creepage Distance As Per IEC 60664

Q: What standard covers clearance and creepage distance?

IEC 60664-1 is the primary standard for insulation coordination in low-voltage equipment and provides the principles used to determine clearance and creepage. Specific product standards may provide additional or modified requirements for particular equipment.

Q: Is creepage distance always greater than clearance?

Not always. Creepage can be greater than clearance, particularly where pollution creates a surface-tracking risk, but the required values depend on working voltage, pollution degree, material group, impulse voltage, insulation type, and other design conditions.

Q: How do I calculate creepage distance?

Creepage is determined using the working voltage, pollution degree, insulation material group, and required insulation type. The applicable tables and rules in IEC 60664-1 should then be used to establish the minimum creepage distance. Product-specific standards may also apply.

Q: Does altitude affect clearance?

Yes. Higher altitude reduces air density and can reduce the dielectric strength of air. Therefore, clearance may need to be increased or corrected for equipment operating above the reference altitude. The applicable altitude correction requirements should be checked in IEC 60664-1.

Clearance and creepage distance are two key insulation requirements used in electrical equipment to prevent flashover, tracking, and insulation failure. IEC 60664-1 provides the basic insulation coordination principles used to determine these distances in low-voltage equipment, assemblies, control panels, power supplies, and other electrical systems.

The required distance is not based on voltage alone. Working voltage, overvoltage category, pollution degree, insulation type, material group, altitude, and the nature of the electrical insulation all affect the final value.

For engineers designing equipment, understanding Clearance and Creepage Distance as per IEC 60664 is essential for safe PCB layouts, terminals, busbars, switchgear, control circuits, and electrical assemblies.

Table of Contents

Quick Reference: Clearance vs Creepage Distance

Parameter	Clearance	Creepage Distance
Definition	Shortest distance through air between conductive parts	Shortest distance along an insulating surface
Main medium	Air	Solid insulation surface
Main concern	Electrical flashover	Surface tracking
Influenced by	Working voltage, impulse voltage, altitude, overvoltage category	Working voltage, pollution degree, material group
Typical application	Air gap between terminals	Distance along PCB or insulator
Measurement path	Straight or shortest air path	Along the insulation surface
Standard reference	IEC 60664-1	IEC 60664-1

What Is Clearance Distance?

Clearance is the shortest distance through air between two conductive parts at different electrical potentials. It is intended to withstand the maximum expected transient and steady-state voltage without an electrical breakdown occurring through the air.

For example, if two terminals inside a control panel operate at different potentials, the air gap between the terminals is their clearance. Increasing this air gap generally improves resistance to flashover.

The clearance requirement is strongly associated with the rated impulse withstand voltage of the equipment. This is important because short-duration voltage surges can be much higher than the normal operating voltage.

Factors that affect clearance include:

Rated working voltage
Rated impulse voltage
Overvoltage category
Altitude
Transient overvoltages
Insulation type
Equipment construction
Applicable product standard

What Is Creepage Distance?

Creepage is the shortest distance between two conductive parts measured along the surface of an insulating material.

Unlike clearance, creepage is particularly affected by contamination on the insulation surface. Dust, moisture, salt, chemicals, and other contaminants can create a conductive path across an insulating surface.

This is why creepage requirements can be considerably greater than clearance requirements in equipment expected to operate in polluted environments.

For example, two PCB tracks may have a sufficient air gap but still fail the creepage requirement if the distance measured along the board surface is too short.

Clearance and Creepage Distance as per IEC 60664: Main Factors

IEC 60664-1 uses insulation coordination principles rather than providing one universal clearance or creepage value for every voltage.

The following parameters should be established before selecting the distance.

Design Parameter	Why It Matters
Working voltage	Determines the continuous electrical stress
Rated impulse voltage	Determines the required resistance to transient overvoltage
Pollution degree	Represents environmental contamination
Material group	Affects resistance to tracking
Overvoltage category	Helps determine transient voltage conditions
Altitude	Reduced air density can reduce dielectric strength
Insulation type	Basic, supplementary, reinforced, or double insulation
Frequency	Can affect applicable voltage considerations
Manufacturing tolerances	Ensure the minimum distance is maintained in production

Pollution Degree and Creepage Distance

Pollution degree is one of the most important considerations when determining creepage.

IEC 60664-1 commonly classifies the environment into four pollution degrees.

Pollution Degree	Typical Environment
Pollution Degree 1	No pollution or only dry, non-conductive pollution
Pollution Degree 2	Normally non-conductive pollution, with occasional temporary condensation
Pollution Degree 3	Conductive pollution or dry non-conductive pollution that becomes conductive due to condensation
Pollution Degree 4	Persistent conductive pollution, such as conductive dust, rain, or wet conditions

A clean, enclosed electronic device may have very different creepage requirements from outdoor industrial equipment.

When selecting Clearance and Creepage Distance as per IEC 60664, the expected installation environment should therefore be defined first.

Material Group and CTI

Creepage requirements also depend on the insulation material’s resistance to tracking.

The Comparative Tracking Index, or CTI, is used to classify insulating materials. Materials with higher CTI values generally provide better resistance to tracking and can allow shorter creepage distances for the same electrical conditions.

Common material groups include:

Material Group	CTI Range
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

The actual material classification should be obtained from the component or insulation manufacturer’s data rather than assumed from appearance or material name alone.

Clearance and Creepage Distance as per IEC 60664 for PCB Design

PCB layout is one of the most common applications of IEC 60664 insulation coordination.

Designers need to consider both the direct air gap between copper features and the surface path across the PCB material.

A PCB may have adequate clearance but inadequate creepage if conductive tracks are routed too close together along the board surface.

Useful PCB design practices include:

Establish the working voltage before routing.
Determine the applicable pollution degree.
Identify the PCB insulation material and CTI.
Determine the required clearance.
Determine the required creepage.
Account for manufacturing tolerances.
Avoid unnecessary copper features inside the insulation path.
Consider slots or cutouts where appropriate.

Slots can sometimes increase the creepage path without requiring a larger overall PCB footprint. However, the resulting geometry must be evaluated against the applicable standard and construction requirements.

Clearance and Creepage for Electrical Panels

Electrical panels contain several potential insulation coordination points, including:

Busbar-to-busbar spacing
Busbar-to-ground spacing
Terminal-to-terminal spacing
Contactor terminals
Circuit breaker terminals
Fuse holders
Control wiring
PCB assemblies
Insulator surfaces

The required dimensions should not be copied from a generic chart without checking the applicable equipment standard.

For assemblies, IEC 61439 may also be relevant because it contains requirements for low-voltage switchgear and controlgear assemblies.

For related equipment spacing requirements, see our guide to phase to phase clearance as per iec 61439, which explains phase-to-phase and phase-to-earth considerations for low-voltage assemblies.

Clearance vs Creepage: Practical Example

Consider a 400 V three-phase electrical assembly. The designer must evaluate the normal working voltage and expected transient conditions.

The clearance is evaluated through air, while creepage is evaluated over the insulation surface.

Design Check	Question
Working voltage	What voltage exists continuously between conductors?
Transient voltage	What impulse voltage can occur?
Pollution	Is the equipment clean, industrial, or exposed?
Insulation	Is it basic, supplementary, or reinforced?
Material	What is the CTI or material group?
Altitude	Will the equipment operate above the reference altitude?
Product standard	Does another product standard specify additional requirements?

This approach prevents a common design mistake: selecting a distance based only on nominal voltage.

Altitude Correction for Clearance

Air insulation becomes less effective at higher elevations because air density decreases. Therefore, equipment installed at significant altitude may require increased clearance or an appropriate correction factor.

This consideration applies primarily to clearance rather than creepage.

Designers should check the applicable altitude correction requirements in IEC 60664-1 and the relevant product standard instead of applying an arbitrary percentage increase.

Basic, Supplementary and Reinforced Insulation

Insulation coordination also depends on the level of protection required.

Insulation Type	Purpose
Functional insulation	Needed for correct equipment operation
Basic insulation	Provides basic protection against electric shock
Supplementary insulation	Independent additional insulation
Double insulation	Combination of basic and supplementary insulation
Reinforced insulation	Single insulation system providing protection equivalent to double insulation

The required clearance and creepage can therefore differ even when two conductors operate at the same voltage.

How to Measure Clearance and Creepage

Correct measurement is important during both design and inspection.

For clearance, measure the shortest distance through air between conductive parts.

For creepage, follow the shortest permissible path along the insulating surface between the conductive parts.

The geometry of ribs, grooves, barriers, and slots can influence the measurement. Not every physical surface automatically creates a valid creepage path, so the measurement method must follow the applicable IEC rules.

Common Mistakes in Insulation Spacing

Several design errors repeatedly appear in electrical equipment.

Using Voltage Alone

A common mistake is to choose a spacing based only on 120 V, 230 V, 400 V, or another nominal voltage. Transient voltage and insulation coordination requirements must also be considered.

Confusing Clearance With Creepage

An air gap and a surface path are different measurements. Passing one requirement does not automatically mean the other is satisfied.

Ignoring Pollution Degree

Equipment installed in an industrial or outdoor environment may need more creepage than equipment operating in a clean, controlled environment.

Ignoring Manufacturing Tolerances

A design that barely meets the minimum distance on CAD drawings may fail during manufacturing because of tolerances, component movement, burrs, or assembly variation.

Copying Values From an Unverified Chart

Generic online tables can be useful for preliminary design, but final dimensions should be verified against the current edition of IEC 60664-1 and the applicable product standard.

Design Checklist

Use this checklist before finalizing insulation spacing:

Identify the maximum working voltage.
Determine the required impulse withstand voltage.
Establish the overvoltage category.
Select the pollution degree.
Determine the insulation material group.
Check the CTI of the insulating material.
Determine the required clearance.
Determine the required creepage.
Apply altitude considerations where required.
Check basic, supplementary, or reinforced insulation requirements.
Include manufacturing tolerances.
Verify requirements in the applicable product standard.

For switchgear and assemblies, also compare the design with the applicable IEC 61439 requirements. Our guide on phase to phase clearance as per iec 61439 can be used as a related reference when evaluating conductor and busbar spacing.

Why IEC 60664 Matters for Electrical Safety

Proper insulation coordination reduces the risk of flashover, arcing, tracking, electric shock, and equipment damage. It also improves the reliability of electrical assemblies operating under normal and abnormal voltage conditions.

For manufacturers, the correct approach is to treat clearance and creepage as part of the complete insulation system rather than as simple physical dimensions.

A reliable design starts by identifying the electrical and environmental conditions, followed by selection of the correct insulation coordination parameters.

When working on low-voltage assemblies, it is also useful to compare the insulation spacing with requirements for phase to phase clearance as per iec 61439, especially where busbars, terminals, and other energized parts are involved.

Frequently Asked Questions

What is the difference between clearance and creepage?

Clearance is the shortest distance through air between two conductive parts. Creepage is the shortest distance along the surface of an insulating material. Both are used to prevent electrical breakdown, but creepage is especially affected by pollution and the tracking characteristics of the insulation material.

What standard covers clearance and creepage distance?