Overview
IEC 63522-21:2025 - "Electrical relays - Tests and measurements - Part 21: Thermal endurance" defines a standardized test method to evaluate the resistance of electrical relays to prolonged high-temperature exposure. The standard is intended to assess relay performance under expected conditions of transportation, storage and operational use, with relays energized at rated coil voltage and carrying specified continuous currents. The preferred test duration is 1 000 h, extendable to 2 000 h and 5 000 h depending on results.
Key topics and requirements
- Purpose: Verify that relays continue to operate correctly (operate/release at specified voltages) after long periods at the upper value of their operating temperature range while energized.
- Test durations (duration levels): Recommended intermediate checks at 72 h, 200 h, 500 h; final measurements at 1 000 h (level A), 2 000 h (level B) and 5 000 h (level C).
- Conditions to be specified: mounting method (PCB, PWB, flat-quick connectors, sockets), mounting distance, maximum ambient temperature (chamber with air recirculation), energization (rated coil voltage), and load (limiting continuous current).
- Sample size: minimum 5 pieces (5–10 recommended).
- Measurements and evaluations:
- Intermediate functional checks per IEC 63522-7 (functional tests).
- Final checks include contact-circuit resistance per IEC 63522-6 and timing per IEC 63522-8.
- Pass criteria: correct switching at operating and release voltages after cooldown to ambient temperature; no malfunction during final functional cycles.
- Reporting: A detailed test report must record DUT description, method, deviations, ambient conditions, voltages/currents, duty cycle, mounting, limiting currents and all observations (see Table 3 of the standard).
Practical applications and users
- Who uses it: relay manufacturers, component qualification and reliability labs, quality assurance engineers, design and test engineers, and certification bodies.
- Why it matters: Thermal endurance testing verifies long-term reliability of relays in high-temperature environments - crucial for industrial control systems, power distribution, automotive control modules, and other applications where relays remain energized under elevated temperatures.
- Benefits: Helps prevent contact failures, high contact resistance and timing drift; informs design choices (materials, cooling, mounting) and supports product claims about thermal lifetime and operational robustness.
Related standards
Keywords: IEC 63522-21, thermal endurance, electrical relays, high temperature testing, relay qualification, contact resistance, limiting continuous current, operating voltage, release voltage, test duration.
