IEC 61643-12:2020

Overview

IEC 61643-12:2020 - Low-voltage surge protective devices (SPDs) - Part 12: Selection and application principles - provides guidance for the selection, location, operation and coordination of SPDs installed on 50/60 Hz AC power circuits and equipment rated up to 1 000 V RMS. This third edition (technical revision of the 2008 edition) focuses on practical application principles for SPDs that contain at least one non‑linear component to limit surge voltages and divert surge currents. The edition adds new guidance on the need for protection, disconnecting devices, measured limiting voltage and SPD characteristics and selection parameters.

Key topics and technical requirements

• Scope and purpose: Principles for selecting and applying SPDs connected to low-voltage power systems (not component-level surge protection inside equipment).
• Need for protection: How to assess when SPDs are required based on environmental and system stresses (lightning, switching, temporary overvoltages).
• SPD classification and topologies: Functional roles, typical designs and modes of connection in LV systems.
• Selection parameters: List of parameters to consider (voltage protection level, impulse current capability, follow‑current rating/SCCR, rated load current, expected lifetime, and voltage coordination).
• Characteristics and testing: Guidance on interpreted test results (measured limiting voltage, surge current behavior) and how characteristics change over life and under stress.
• Coordination principles: Energy coordination between multiple SPDs, let‑through energy concepts and practical coordination techniques to protect downstream equipment.
• Auxiliary devices: Requirements for disconnecting devices, status indicators, surge/event counters and other auxiliaries for safe operation and maintenance.
• Informative annexes: Risk assessment methods, application examples (domestic, industrial, wind turbines), environment and system stress analysis, and coordination test protocols.

Applications and users

IEC 61643-12:2020 is intended for professionals involved in specifying, installing and maintaining surge protection in low-voltage power systems:

• Electrical designers and consultants selecting SPDs for buildings, industrial plants, substations and renewable-energy systems (e.g., wind turbines).
• Installers and contractors implementing SPD location, modes of protection and coordination with distribution equipment.
• Facility managers and asset owners assessing protection needs and lifecycle expectations.
• Manufacturers and test labs referencing selection parameters and characteristics when developing or verifying SPDs.

Practical uses include defining SPD location in an installation, choosing appropriate voltage protection levels (U_p), ensuring coordination between upstream and downstream devices, and verifying safe disconnection and status monitoring.

Related standards

• IEC 61643-11 - SPD product and test requirements (complements Part 12 for testing/verification).
• IEC 60364 and IEC 62305-4 - electrical installation and lightning protection guidance referenced for risk assessment and installation practice.
• Note: USA practice differs - SPDs tested to Class I tests are not always required (document exception).