IEC 61643-331:2017

Overview

IEC 61643-331:2017 - Components for low-voltage surge protective devices - Part 331 - specifies performance requirements and test methods for metal oxide varistors (MOV). It applies to two‑electrode MOVs and hybrid overvoltage protection components used in circuits up to 1 000 V AC or 1 500 V DC for power line, telecommunication, and signalling applications. This second edition (2017) replaces the 2003 edition and introduces several technical revisions including test updates for nominal varistor voltage, thermally protected MOVs, and nominal discharge current.

Key Topics and Requirements

The standard defines measurable electrical, mechanical and environmental requirements and standardized test procedures, including:

• Nominal varistor voltage - updated test method to determine the V‑I characteristic reference point.
• Maximum continuous operating voltage and standby (leakage) current tests.
• Clamping voltage measurement at peak impulse current (test circuits and currents defined).
• Rated impulse energy and nominal discharge current (In) - new test methods and pass/fail criteria.
• Endurance and accelerated ageing tests to verify long‑term performance under repeated transient stress.
• Thermally protected varistors - added component symbol, test procedures, and limited current / temporary overvoltage tests specific to these devices.
• SMD and disc type specifics - addition of voltage rating tables and test currents for disc and typical ratings for SMD MOVs.
• ESD testing (for SMD MOVs), capacitance measurement, dielectric and robustness tests (solderability, terminations, marking).
• Environmental and service conditions - operating/storage temperature ranges, humidity and altitude considerations.
• Informative annexes: cross‑references to IEC 61643‑11 testing, IEC 61051 varistor background, accelerated screening, and methods for estimating mean time to failure (MTTF).

Note: The standard excludes effects introduced by specific mountings; test characteristics apply only to the MOV mounting methods described.

Applications and Who Uses It

IEC 61643-331 is essential for:

• MOV manufacturers for product specification, design verification and marking.
• Test laboratories and certification bodies performing type and routine testing.
• Surge protective device (SPD) designers integrating MOVs into power, telecom and signalling protective solutions.
• Compliance engineers and procurement teams who specify components to meet safety and performance requirements.
• OEMs of power distribution, industrial control and telecommunications equipment where protection against high transient voltages is required.

Using this standard helps ensure MOVs reliably limit high transient voltages, meet safety expectations, and perform predictably in specified service conditions.

Related Standards

• IEC 61643 series (e.g., IEC 61643‑11) - SPDs for power systems (referenced in Annex A).
• IEC 61051 - varistor guidance for electronic equipment (referenced in Annex B).
• Other IEC test and safety standards relevant to SPD design and qualification.