IEC 60287-2-1:2015

Overview

IEC 60287-2-1:2015 - part of the IEC 60287 series - defines methods to calculate the thermal resistance of electric cables for steady-state operation. It applies to cables at all alternating voltages and direct voltages up to 5 kV, installed buried (directly, in ducts, troughs or steel pipes) or in air, and covers situations with and without partial drying-out of the soil. The standard supplies formulae, tables and graphical data needed when determining cable thermal resistances used in ampacity (current rating) calculations.

Key topics

• Scope and steady-state assumption: calculations assume a continuous constant current (100% load factor) and constant ambient conditions leading to the maximum conductor temperature.
• Internal and external thermal resistance: methods for thermal resistance of cable constituents (conductor–sheath–armour–serving) and external thermal resistance for cables in free air, ducts, pipes, troughs and buried installations.
• Installation cases: single buried cables, groups of buried cables (touching and not touching), cables in ducts, pipes and troughs, pipe-type cables and cables in air.
• Graphical and digital methods: guidance for converting graphical data to numerical results; geometric factor G for two- and three-core belted cables; curves for screened cables and filling materials (SL and SA types).
• Updated technical provisions (2015 edition): reference to finite element methods (FEM) where analytical solutions are not available; clarification on SL and SA cable types; method for T3 (unarmoured three-core extruded-insulation cables with individual copper tape screens); revised condition for parameter X in clause 5.4; added constants for water-filled ducts in Table 4.
• Supporting data: tables of thermal resistivities, heat dissipation coefficients, solar absorption and constants used in calculation formulae.

Applications and users

• Cable designers and manufacturers calculating conductor temperatures and ampacity (current rating).
• Power utilities and network planners selecting cable types and installation methods for reliable load capacity.
• Consulting engineers and system integrators assessing thermal performance for buried or ducted cable routes.
• Standards writers and test labs using the standard as the reference for uniform thermal-resistance inputs. This standard is used together with IEC 60287 Part 1 (ratings and power losses) and Part 3 (operating conditions) for full ampacity calculations.

Related standards

• IEC 60287 series - Electric cables - Calculation of the current rating
• IEC 60287-1 (Part 1: formulae of ratings and power losses) and IEC 60287-3-1 (guidance on parameter selection and operating conditions)

Keywords: IEC 60287-2-1, thermal resistance, cable ampacity, current rating, buried cables, ducts, finite element methods, SL SA cables, water-filled ducts.