IEC 60287-2-3:2024

Overview - IEC 60287-2-3:2024 (Electric cables - Current rating - Ventilated tunnels)

IEC 60287-2-3:2024 specifies a calculation method for the continuous current rating factor of electric cables of all voltages when installed in ventilated tunnels. The standard addresses both natural and forced ventilation and is applicable to any cable type. It assumes steady-state conditions, identical cables throughout the tunnel, a constant tunnel cross-section, and that longitudinal heat transfer within the cables and surrounding materials is negligible (although convective heat removal by air flow along the tunnel is treated).

Keywords: IEC 60287-2-3:2024, current rating calculation, thermal resistance, ventilated tunnels, cable ampacity, forced ventilation, natural ventilation.

Key technical topics and requirements

• Thermal modelling for ventilated tunnels: Provides formulae to calculate thermal resistances influencing cable temperatures under airflow conditions.
• Heat-transfer mechanisms covered:
  • Radial conduction within the cable
  • Radiation from cable surface to inner tunnel wall
  • Convection from cable to tunnel air and from air to tunnel wall
  • Longitudinal convective heat transfer by air moving along the tunnel
  • Radial heat conduction in surrounding soil/tunnel structure
• Assumptions and flow regimes:
  • Steady-state loading and inlet-air temperature
  • Air flow treated as laminar or turbulent (transitional regime ignored)
  • Identical cable circuits and uniform tunnel cross-section
• Calculation approach:
  • A defined set of formulae for thermal resistances and air properties
  • Iterative solution procedures and guidance to obtain temperature profiles and allowable current
  • Informative annexes (calculation example, delta–star transformation, C coefficient) to support practical use

Practical applications - who uses this standard

• Electrical engineers and cable designers sizing cable ampacity in tunnels (road, rail, utility or industrial tunnels)
• Power utilities and transmission planners assessing continuous ratings for underground routes with ventilation
• Tunnel and ventilation engineers integrating thermal performance with HVAC and safety systems
• Consulting firms performing thermal assessments, regulatory compliance checks, and safety studies
• Test laboratories and certification bodies referencing standardized calculation methods

Practical outcomes include reliably calculating cable ampacity, designing ventilation strategies to control cable temperatures, and ensuring safety and compliance in tunnel cable installations.

Related standards

• IEC 60287-1-1 - Current rating equations and loss calculations (general)
• IEC 60287-2-1 - Thermal resistance calculation methods for cables in free air
• Other parts of the IEC 60287 series for grouping and installation-specific factors

Using IEC 60287-2-3:2024 helps professionals produce consistent, standardized current-rating calculations for cables in ventilated tunnels and supports sound decisions on ventilation, cable selection, and thermal safety.