Overview
IEC 61921:2017 - "Power capacitors - Low-voltage power factor correction banks" is the International Electrotechnical Commission standard that defines requirements, tests and guidance for low-voltage AC shunt capacitor banks used for power factor correction. This second edition (2017) supersedes the 2003 edition and introduces a technical revision that aligns verification methods with IEC 61439-1, updates marking and routine tests (including routine verification of rated output), and adds Annex D with guidance on temperature-rise verification.
Key Topics
- Scope and applicability: Requirements for low-voltage AC shunt capacitor banks intended for power factor correction, including assemblies with built‑in switchgear and controlgear.
- Design and installation guidance: Recommendation on rated voltage selection, switching and overload protection, electrical environment and secondary effects of capacitor banks.
- Safety measures: Discharging devices and procedures after disconnection, fire-hazard considerations, protection against human and property damage, and busbar/connection rules.
- Verification and testing:
- Design verification: Dielectric properties, temperature-rise limits, short-circuit withstand strength, mechanical operation, EMC and component incorporation.
- Routine tests: Degree of protection of enclosures, clearances and creepage, dielectric tests, mechanical operation and verification of rated output.
- New Annex D: Guidance on methods for temperature-rise verification when adding capacitors for test purposes.
- Electromagnetic compatibility (EMC): Emission and immunity requirements plus considerations for assemblies that incorporate electronic equipment.
- Marking and documentation: Updated marking requirements and normative references to ensure traceability and safe installation.
- Informative annexes: Practical formulae, typical assembly examples and conductor sizing guidance.
Applications
IEC 61921:2017 is directly applicable to:
- Industrial and commercial power factor correction (PFC) systems
- Distribution boards and low-voltage reactive compensation plants
- Retrofit and new-build electrical installations where capacitor banks are integrated with switchgear/controlgear
- Situations requiring formal type and routine testing of capacitor bank assemblies
Using the standard helps ensure safe operation, predictable temperature behavior, proper protection against overvoltages/overloads, and compliance with recognized verification methods.
Who should use this standard
- Manufacturer and designer of capacitor banks and PFC equipment
- Electrical engineers specifying reactive compensation systems
- Panel builders and switchgear integrators
- Testing laboratories and conformity assessment bodies
- Consultants, installers and utilities responsible for safe, compliant low-voltage installations
Related standards
IEC 61921:2017 references and is intended to be used alongside IEC 61439-1 and IEC 61439-2 (requirements for low-voltage switchgear and controlgear assemblies) and relevant capacitor standards such as IEC 60831 / IEC 60931.