IEC 60664-1 - Insulation Coordination for Low-Voltage Equipment

Creepage vs clearance

Key facts

Full title

Insulation coordination for equipment within low-voltage supply systems - Part 1: Principles, requirements and tests

Published by

IEC (TC 109, Insulation co-ordination for low-voltage equipment)

Current edition

3rd edition, IEC 60664-1:2020, with Amendment 1:2025 (published 6 May 2025)

Scope

Equipment rated up to AC 1000 V or DC 1500 V, at frequencies up to 30 kHz, altitude up to 2000 m (correction factors above)

Sets

Clearance (through air), creepage (along a surface) and solid-insulation requirements

Key inputs

Working voltage, overvoltage category, pollution degree and material group (CTI)

Role

A horizontal base standard; product safety standards derive their spacing tables from it

Clearance and creepage: two different failures

The standard sizes two distances that fail in different ways. Clearance is the shortest distance through air between two conductive parts. It is set by the peak or impulse voltage the insulation must survive, ranked by the overvoltage category, and it guards against a fast breakdown of the air gap.

Creepage is the shortest path along the surface of the insulation between the same two parts. It is set by the RMS or DC working voltage together with the pollution degree and the material's tracking resistance, and it guards against a slow build-up of a conductive track across the surface over the product's life. Because they answer different questions, clearance and creepage are calculated separately and one is often larger than the other.

Pollution degree

Pollution degree describes the microenvironment around the insulation, from clean and dry conditions through contamination that can become or remain conductive. It is not assigned simply from labels such as indoor, office or industrial; condensation, deposits, enclosure protection and the actual local surface condition matter.

Pollution degree mainly affects creepage and can also affect minimum clearance conditions. Assess it under the applicable product standard and verified construction rather than transferring a room description directly into a spacing table.

Material group and CTI

The insulating material is classified into one of four groups by its comparative tracking index (CTI), a measured value of how well the surface resists forming a conductive track under contamination and voltage.

A material with a lower CTI tracks more easily and therefore needs a longer creepage distance for the same working voltage and pollution degree. The CTI itself is measured by the method in IEC 60112.

Overvoltage category

The overvoltage category is an insulation-coordination input describing the transient environment associated with the equipment's connection within a low-voltage supply system. Together with the applicable system voltage it is used to select a rated impulse withstand level for clearance design.

Do not automatically substitute a measurement CAT marking from IEC 61010 for this overvoltage-category input. The concepts both concern transient environments, but they belong to different rule sets and must be selected under the standard that applies to the equipment and circuit.

How product standards use it

IEC 60664-1 is a horizontal basic safety publication. Its public scope says it provides requirements for technical committees to determine clearances, creepage distances and solid-insulation criteria; it does not by itself decide the complete construction for every product.

Product safety standards such as members of the IEC 61010 or IEC 62368 families apply their own scope, conditions and particular requirements. Start with the product standard, then use IEC 60664-1 where that standard invokes or aligns with its insulation-coordination method.

Material groups by comparative tracking index (CTI)

Tools that use this standard

Related standards

Frequently asked questions