IEC 61643-331:2020

Overview

IEC 61643-331:2020 - Components for low-voltage surge protection - Part 331: Performance requirements and test methods for metal oxide varistors (MOV) - is the third edition (technical revision) of the MOV test specification. It applies to two‑electrode and hybrid MOV components used in applications up to 1 000 V AC or 1 500 V DC for power lines, telecommunications or signalling circuits. The standard defines performance criteria and laboratory test methods intended to verify MOV behaviour for protection of equipment and personnel against high transient voltages. This edition introduces significant updates including a Varistor MCOV rating assurance test, an energy rating test (2 ms) and revised dielectric strength and insulation resistance tests.

Key topics and technical requirements

• Scope and applicability

  • MOVs with two electrodes and hybrid surge protection components for low-voltage systems (power, telecom, signalling).
  • Excludes effects of mountings unless tests specify mounting arrangements.

• Electrical characteristics and ratings

  • Nominal varistor voltage (Vn), clamping voltage (Vc), maximum continuous operating voltage (MCOV), standby/leakage current, capacitance.
  • New MCOV rating assurance to confirm continuous operating voltage claims.
  • Energy rating (2 ms) test to quantify short-duration energy capability.

• Performance and endurance tests

  • Nominal discharge current (In) and single-impulse maximum current tests.
  • Endurance / operating duty tests and accelerated endurance screening.
  • Limited current temporary overvoltage and thermally protected varistor sequences.
  • Dielectric strength and insulation resistance measurements (revised in this edition).
  • ESD testing for SMD MOV types.

• Quality and reliability

  • Annexes address test methods for operating duty, accelerated endurance, and a proposed MTTF determination method.
  • Marking, solderability and mechanical robustness requirements are included.

Practical applications and users

• Who uses IEC 61643-331:

  • MOV manufacturers validating product performance and ratings.
  • Certification and independent test laboratories performing compliance testing.
  • Designers and engineers of surge protective devices (SPDs), power distribution, telecommunications and signalling equipment.
  • Procurement/specification writers and regulatory bodies that require traceable performance criteria for surge protection components.

• Practical value:

  • Ensures MOVs meet minimum safety and functional performance under transient stress.
  • Guides designers in selecting MOVs with verified MCOV, energy handling and clamping behaviour.
  • Supports consistent testing for product qualification and comparative evaluation.

Related standards

• IEC 61643-11 - Surge protective devices for Class I, II and III (referenced in annex A).
• IEC 61051 - Varistors for use in electronic equipment (referenced in annex B).

For complete test procedures, pass/fail criteria and normative details, obtain the full IEC 61643-331:2020 text from the IEC Webstore.