IEC 60255-5

Overview

IEC 60255-5 defines the general requirements for insulation coordination of measuring relays and protection equipment. The standard provides guidance for designers, test engineers and manufacturers on selecting appropriate clearances and creepage distances, and describes the required procedures for voltage tests and insulation resistance measurements. Its objective is to support safe, reliable and compliant relay design and testing without prescribing circuit- or product‑specific numeric values.

Key Topics

• Scope and purpose: General principles for insulation coordination applied to measuring relays and protection equipment.
• Clearances and creepage: Guidance on selecting physical separation and surface distance to control breakdown and tracking risks.
• Insulation aspects: Consideration of materials, pollution degree and environmental conditions that affect dielectric behavior.
• Voltage testing: Specification of test types and conditions to verify dielectric withstand capability and construction integrity.
• Insulation resistance measurement: Requirements for verifying resistance levels that indicate acceptable insulation condition.

These topics emphasize practical, testable measures that reduce the risk of internal arcing, flashover, or progressive insulation degradation in protection systems.

Applications

IEC 60255-5 is directly applicable to the following use cases:

• Design and development of measuring relays and protection equipment, ensuring that insulation design aligns with operational and environmental demands.
• Production testing and type approval, where manufacturers confirm compliance with insulation coordination requirements before market release.
• Maintenance and service verification, using specified voltage and insulation resistance tests to assess ongoing insulation health.
• Equipment selection for utilities and industrial installations where relay reliability and personnel safety are critical.

Benefits include improved operational reliability, reduced failure risk, clearer product specifications for procurement, and support for regulatory or contractual compliance.

Related Standards

• Other parts of the IEC 60255 series (relays and relay requirements) provide complementary requirements for electrical, mechanical and functional aspects of protection devices.
• General IEC guidance on insulation coordination and dielectric testing may be referenced to address system‑level considerations and specific test methodologies.

For engineers and compliance professionals, IEC 60255-5 serves as a practical reference for integrating insulation coordination into relay design, testing routines and procurement specifications. Its focus on clearance, creepage, voltage tests and insulation resistance makes it essential for achieving durable, safe protection equipment.