IEC TS 63346-2-3-2025 PDF

Full title and description

IEC TS 63346-2-3:2025 — Low-voltage auxiliary power systems - Part 2-3: Design criteria - Low-voltage AC auxiliary power systems for substations. This technical specification sets out common rules and requirements for the design of low-voltage AC auxiliary power systems (APSs) intended to be installed in electrical substations, covering configuration of AC power sources, system wiring, protection, electrical equipment selection and physical layout for LV AC APSs up to and including 1 kV AC.

Abstract

This Technical Specification provides guidance and normative criteria to assist designers, engineers and asset owners in specifying and implementing low-voltage alternating-current auxiliary power systems in substations. It focuses on architecture and design aspects such as source configuration, redundancy, earthing/grounding, conductor routing, protection coordination, equipment selection and spatial arrangement, while excluding detailed requirements for the high-voltage side and detailed AC load characteristics. The document treats AC APSs with nominal voltages up to and including 1 kV.

General information

• Status: Published.
• Publication date: 6 November 2025 (Edition 1.0).
• Publisher: International Electrotechnical Commission (IEC).
• ICS / categories: 29.240 - Power transmission and distribution networks.
• Edition / version: Edition 1.0, 2025.
• Number of pages: 31 pages (PDF publication).

Scope

IEC TS 63346-2-3:2025 specifies common rules and requirements for the design of low-voltage AC auxiliary power systems (APSs) intended to be installed in substations. It applies to AC APSs with nominal voltages up to and including 1 kV AC and addresses configuration of AC power sources, wiring, protection, equipment selection and physical layout. The document does not attempt to define specific AC load performance for all applications and does not provide requirements for the high-voltage equipment of the substation beyond where interaction with the LV APS is necessary.

Key topics and requirements

• Design principles for LV AC auxiliary power systems for substations (nominal voltage ≤ 1 kV AC).
• Recommended configurations for AC power sources, including redundancy and source selection strategies.
• System wiring practices, conductor routing and segregation of circuits to improve reliability and maintainability.
• Protection and coordination requirements for APS circuits and associated switchgear.
• Selection criteria for electrical equipment used within LV AC APSs (transformers, switchgear, protection devices, distribution boards).
• Physical layout and installation guidance addressing accessibility, separation, and fire/safety considerations in substation environments.
• Interfaces and limits of applicability: clarifies where AC loads and HV systems are out of scope and where interaction must be considered.

Typical use and users

This Technical Specification is intended for electrical engineers, system designers, substation project managers, consultants, equipment manufacturers and asset owners responsible for specifying or installing LV AC auxiliary power systems in substations. It is used as a design reference to define required architectures, reliability levels and installation practices, and is also useful for procurement teams preparing technical specifications for equipment and systems. Commercial national adoptive publications (PD/identical national editions) are available from several standards bodies for local use.

Related standards

IEC TS 63346-2-3:2025 is part of the IEC 63346 series addressing low-voltage auxiliary power systems. Related and complementary documents include the terminology and Part 1 documents (for example IEC TS 63346-1-1, terminology for LV auxiliary power systems) and national/adopted versions such as the BSI PD IEC TS 63346-2-3:2025 edition. These related documents provide terminology, higher-level principles and other part-specific guidance across the APS lifecycle.

Keywords

auxiliary power system, APS, low-voltage, LV AC, substation, design criteria, redundancy, protection coordination, wiring, equipment selection, IEC 63346.

FAQ

Q: What is this standard?

A: IEC TS 63346-2-3:2025 is a Technical Specification that defines design criteria for low-voltage alternating-current auxiliary power systems used in electrical substations, focusing on architecture, wiring, protection and equipment selection.

Q: What does it cover?

A: It covers LV AC APSs with nominal voltages up to and including 1 kV AC and provides requirements and recommendations for source configuration, wiring practices, protection coordination, equipment selection and physical layout; it explicitly limits detailed HV and full AC load performance requirements to the extent they lie outside the APS design remit.

Q: Who typically uses it?

A: Electrical engineers, substation designers, consultants, project managers, equipment manufacturers and asset owners use this specification when designing, specifying or procuring LV AC auxiliary power systems for substations. National publishers also distribute PD/identical versions for local use.

Q: Is it current or superseded?

A: This document is current; it was published in November 2025 (Edition 1.0) and the IEC record lists a stability date extending to 2028. Users should check for later revisions or related normative publications before applying the text to long-term projects.

Q: Is it part of a series?

A: Yes — IEC TS 63346-2-3:2025 is part of the IEC 63346 family addressing low-voltage auxiliary power systems; related parts include terminology and other part-specific guidance (for example IEC TS 63346-1-1). National/PD adoptions exist for some markets.

Q: What are the key keywords?

A: Key keywords include: auxiliary power system, LV AC, substation power, design criteria, redundancy, protection coordination, wiring practices, equipment selection.