Overview
IEC 60287-2-1:2023 - “Electric cables - Calculation of the current rating - Part 2-1: Thermal resistance - Calculation of thermal resistance” is an IEC international standard that defines methods to calculate the thermal resistance of electric cables under steady-state conditions. It applies to cables at all alternating voltages and to direct voltages up to 5 kV, for installations buried directly in ground, in ducts, in troughs or steel pipes (with or without partial soil drying‑out), and for cables in air. “Steady‑state” is taken as a continuous constant current (100% load factor) producing the maximum conductor temperature with fixed ambient conditions.
Key topics
- Internal thermal resistance: modelling of constituent cable parts (conductor-to-sheath, annular layers, sheath-to-armour, outer serving, pipe‑type construction).
- External thermal resistance: methods for cables in free air, single buried cables, groups of buried cables (touching and non‑touching), cables in troughs, ducts, pipes and different surrounding media.
- Geometric factors and graphical data: digital calculation procedures for quantities provided graphically (geometric factor G, diagrams for Δθ calculation).
- Material data and constants: tabulated thermal resistivities, heat dissipation coefficients, solar absorption and other constants to ensure consistent cable ampacity calculations.
- Corrections and special cases: corrective factors for increased lengths of individual cores within multicore cables (Annex A), treatment of multilayer/annular geometries and improved formulations for duct banks and backfills.
- Edition updates: 3rd edition (2023) includes redefined symbols, added materials, generic annular layer modelling and improved calculation methods.
Applications
- Calculate cable thermal resistance as an input to cable current rating (ampacity) and power‑loss assessments.
- Perform thermal modelling for cable route design: direct burial, duct banks, troughs and aerial installations.
- Support selection and specification of cable types, backfill materials and installation spacing to meet thermal limits.
- Aid thermal risk assessment for utilities, industrial power distribution, renewable energy and transmission projects.
Who uses this standard
- Electrical and cable design engineers, thermal analysts and consultants
- Cable manufacturers and test laboratories
- Transmission & distribution utilities and asset owners
- Contractors specifying installation methods and backfill materials
- Standards committees and regulatory bodies for interoperability and safety compliance
Related standards
- Other parts of the IEC 60287 series (Part 1: rating formulae; Part 3: operating conditions)
- IEC 60287-3-1 (guidance on selecting environmental and soil parameters)
Keywords: IEC 60287-2-1, electric cables, current rating, thermal resistance, steady‑state operation, buried cables, cables in ducts, cable ampacity, thermal modelling.
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