IEC 61557-5:2019

Overview

IEC 61557-5:2019 specifies requirements for measuring equipment that measures resistance to earth (earth resistance) using an AC voltage in low voltage distribution systems up to 1 000 V AC and 1 500 V DC. This third edition (2019) replaces the 2007 edition and is a technical revision that clarifies definitions, restructures requirements, and adds new requirements for clamps, marking, safety warnings and measurement uncertainty. The standard is intended to ensure reliable and safe testing, measuring and monitoring of protective measures related to earth resistance.

Key topics and technical requirements

• Scope and intent: Applies to instruments used to measure resistance to earth (real part of impedance to earth) with AC test voltages.
• Output voltage: Test output between terminals E and H must be an AC voltage without a DC component; frequency and waveform shall be chosen to minimize influence from system interference.
• Disturbance voltage and interference: Manufacturers must state values of influencing voltages from AC or DC distribution-system currents in the operating instructions.
• Operating uncertainty: The term “operating uncertainty” replaces “percentage operating uncertainty”; calculation equation corrected in Table 1. Maximum permissible uncertainty within the marked measurement range is specified for user information.
• Probes and auxiliary electrodes: Requirements cover permissible resistances of probe and auxiliary earth electrodes and appropriate terminal marking (E, H, S, ES).
• Clamps and earth loop testing: New requirements and an informative Annex A describe test configurations for loop clamps used to measure earth loop resistances.
• Marking and instructions: Clause 5 adds marking for rated voltages to earth, measurement category, and warnings (including absence of hazardous voltage).
• Electrical safety: Equipment must comply with general safety requirements in IEC 61557-1 and referenced safety standards.

Practical applications and users

IEC 61557-5 is used by:

• Manufacturers of earth resistance testers, earth loop clamps and protective-measure test equipment to design and label compliant instruments.
• Test laboratories and calibration houses verifying instrument performance and operating uncertainty.
• Electrical installers, verification engineers and maintenance teams performing earthing/grounding testing on low-voltage installations.
• Certification bodies and safety assessors assessing conformity with measurement and safety requirements.

Keywords: IEC 61557-5, resistance to earth, earth resistance, earth loop clamps, low voltage distribution systems, operating uncertainty, testing equipment, auxiliary earth electrode.

Related standards

• IEC 61557-1:2019 (general requirements)
• IEC 60364-6 (installation verification)
• IEC 61010 series; IEC 61243-3 (voltage detectors) - normative references cited in the standard.