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