IEC 60287-3-1:2017

Overview

IEC 60287-3-1:2017 - part of the IEC 60287 series on electric cable current rating - defines site reference operating conditions for the steady‑state calculation of cable current ratings (ampacity). It applies to cables at all alternating voltages and to direct voltage systems up to 5 kV, whether buried directly in ground, in ducts, troughs or steel pipes (with or without partial soil drying), or in air. The standard explains how to choose reference ambient temperatures and soil thermal resistivity values used with the formulae in the IEC 60287 parts that compute current rating and thermal resistance. Note: national requirements take precedence over the general reference values in this document.

Key Topics

• Scope and steady‑state definition: steady state is a continuous constant current (100% load factor) producing the asymptotic maximum conductor temperature under constant ambient conditions.
• Site reference conditions: guidance on selecting ambient temperatures and soil thermal resistivities for current‑rating calculations.
• Procedures when national values are missing: methods and considerations to establish appropriate reference values (e.g., ambient temperature at sea level, soil resistivity, solar radiation).
• Country‑specific data: Annex A provides an updated list of national laying/operating conditions (reference values by country).
• Document changes: this 2017 edition updates Annex A and removes the prior Clause 5 concerning purchaser information for cable selection.
• Supporting tables: includes tables for ambient temperatures and soil thermal resistivity that feed into ampacity and thermal resistance calculations.

Applications

• Determining current rating (ampacity) for power and control cables under steady operating conditions.
• Performing thermal analysis for cable installations (buried, ducted, piped, or aerial).
• Informing cable sizing, installation planning and lifecycle expectations based on site thermal conditions.
• Creating specifications and performing compliance checks for utilities, EPC contractors, and infrastructure projects where environmental/soil parameters influence cable performance.

Who should use this standard

• Electrical design engineers and cable system designers
• Utility planners and asset managers
• Cable manufacturers and test laboratories
• Consultants preparing installation specifications and ampacity studies
• Standards writers and regulatory bodies comparing national laying conditions

Related standards

• IEC 60287 (full series) - formulae for current ratings and thermal resistance (Part 1: ratings; Part 2: thermal resistance)
• IEC 60183 - Guide to the selection of high‑voltage cables (referenced for supplementary guidance)

Keywords: IEC 60287-3-1:2017, electric cables, current rating, ampacity, soil thermal resistivity, site reference conditions, steady‑state operation, buried cables, ambient temperature.