IEC 61557-4:2019

Overview - IEC 61557-4:2019 (Resistance of earth connection and equipotential bonding)

Standard Reference: IEC 61557-4:2019
This IEC standard defines requirements for equipment used to measure the resistance of earth connections, protective earth conductors and equipotential bonding conductors in low-voltage distribution systems (up to 1 000 V AC and 1 500 V DC). It specifies required measurement ranges, performance limits, marking and user information, safety/overvoltage behaviour and tests for operating uncertainty. The 2019 edition is a technical revision that updates measurement category guidance, DC measurement requirements, operating uncertainty formulation and aligns structure with the wider IEC 61557 series.

Key topics and technical requirements

• Scope & application: Equipment for measuring earth conductor resistance and equipotential bonding with value indication or limit indication.
• Measurement categories: Devices intended for distribution systems must be rated Measurement Category III; devices for electrical equipment Measurement Category II (per IEC 61010-2-030).
• Measuring voltage & current:
  • Measuring voltage can be AC or DC; open-circuit voltage must be between 4 V and 24 V.
  • Measuring current within the minimum range shall be at least 0.2 A.
• Measuring range & resolution:
  • Operating uncertainty guaranteed over the range that must include 0.2 Ω to 2 Ω.
  • Digital instruments: resolution at least 0.1 Ω.
  • Analogue scales: marked range must occupy ≥50% of scale length; scale division at least 0.5 mm per 0.1 Ω.
• DC measurement: Equipment using DC must provide a reversing switch or allow interchanging of test leads to avoid polarization errors.
• Operating uncertainty: Maximum permitted operating uncertainty ±30% within the marked measuring range (per standard test conditions).
• Safety & overvoltage: Equipment must not expose the user to danger nor be damaged if accidentally connected to 120% of nominal system voltage.
• Marking & instructions: Devices must display open-circuit voltage, measuring current, rated system voltages, measuring range, rated voltage-to-earth and measurement category. Operating instructions must include warnings (e.g., measure on de-energized circuits), battery life info and guidance for dual-polarity DC readings.

Applications - who uses IEC 61557-4:2019

• Manufacturers of earth-resistance testers and clamp meters to ensure product compliance and safety.
• Electrical contractors and site inspectors performing earthing and bonding verification in installations.
• Maintenance and safety engineers responsible for periodic testing of protective earths and equipotential bonding.
• Calibration and test laboratories developing test procedures and uncertainty budgets for earth-resistance equipment.
• Certification bodies assessing conformity to low-voltage electrical safety testing standards.

Related standards

• IEC 61557-1:2019 - General requirements for protective-measure test equipment
• IEC 61010-2-030 & IEC 61010-031 - Safety requirements for measurement equipment and probes

Keywords: IEC 61557-4:2019, earth resistance testing, equipotential bonding, low voltage distribution systems, protective earth conductors, measurement uncertainty, measurement category, open-circuit voltage.