IEC 61557-7:2019

Overview

IEC 61557-7:2019 - part of the IEC 61557 series - specifies requirements for measuring equipment used to test phase sequence in three‑phase low‑voltage distribution systems (up to 1 000 V AC and 1 500 V DC). It covers portable and fixed phase sequence indicators that give mechanical, visual and/or audible indications. The standard applies to dedicated phase sequence measuring equipment only (it does not apply to monitoring relays or instruments whose primary function is a different measurement).

This third edition (2019) is a technical revision of the 2007 edition and aligns structure and safety requirements with related IEC 61010 standards, expands marking and operating instruction guidance, introduces test leads for insulated conductors, and adds Annex B with phase sequence test information.

Key Topics

• Scope & definitions - what constitutes a phase sequence indicator and which equipment is covered/excluded.
• Indication performance - phase sequence must be unambiguous between 85 % and 110 % of nominal system voltage and within 95 %–105 % of nominal frequency; indication must resist visual/audible interference.
• Safety & construction
  • Portable equipment: double or reinforced insulation (Class II) and insulating enclosures.
  • Suitable for continuous operation.
  • Must withstand 120 % of rated system voltage without damage or user hazard.
• Leakage current limit - when one or two leads are earthed and remaining leads connected to phases, total current to earth shall not exceed 3.5 mA r.m.s. (phase conductors at 110 % rated voltage).
• Leads and connectors - leads require minimum dimensions and construction: outer diameter ≥ 3.5 mm, copper cross‑section ≥ 0.75 mm², individual wire diameter ≤ 0.07 mm, and double/reinforced insulation. Leads shall be permanently attached or use plug devices with live parts inaccessible (per IEC 61010‑3‑031).
• Mechanical and electrical tests - drop, shock, overvoltage, leakage current and marking tests; Annex A/B provide test illustrations and phase sequence test guidance.

Applications and Users

IEC 61557-7 is intended for:

• Electricians and commissioning engineers verifying correct phase rotation during installation or maintenance.
• Maintenance and testing teams in industrial, utility and commercial three‑phase systems.
• Manufacturers and designers of phase sequence indicators and portable test equipment.
• Inspection bodies and conformity assessment laboratories performing type or routine tests.

Typical uses include motor and transformer commissioning, verifying correct supply phase order before connecting rotating equipment, and safety checks during installation.

Related Standards

• IEC 61557-1:2019 - General requirements for equipment testing protective measures.
• IEC 61010-1 / IEC 61010-031 / IEC 61010-2-030 - safety requirements for electrical measuring and test equipment.
• IEC 60417, Electropedia and other IEC 61557 parts for protective‑measure testing.

Keywords: IEC 61557-7:2019, phase sequence, phase sequence indicator, three‑phase distribution systems, low voltage, measuring equipment, test leads, IEC 61010.