IEC 60287-1-2:2023

Overview

IEC 60287-1-2:2023 - "Electric cables – Calculation of the current rating – Part 1‑2" specifies a method to calculate sheath eddy current loss factors for single‑core cables arranged as a three‑phase double circuit in flat formation. The standard provides tabulated coefficients and calculation guidance to correct sheath loss factors for two adjacent circuits where sheaths are bonded at one point or cross‑bonded (i.e., no significant sheath circulating currents). It clarifies when corrections are negligible and when the tabulated coefficients should be applied.

Key topics and requirements

• Scope: Eddy current losses in metallic sheaths of two circuits in flat formation; assumes sheaths are bonded to avoid significant circulating currents. Circulating current cases (sheaths bonded at both ends) are treated in IEC 60287‑1‑3.
• Loss correction coefficients: Tabulated coefficients derived from fundamental loss formulae are provided to correct single‑circuit sheath loss factors for mutual circuit influence.
• Parameter m: The correction is negligible when m = ω/(Rs · 10^7) is less than ~0.1 - corresponding to a sheath longitudinal resistance > ~314 µΩ/m at 50 Hz. This means the method is typically required for most aluminium‑sheathed cables but usually not for lead‑sheathed cables unless unusually large.
• Interpolation and computation: Coefficients are given in tables and may require interpolation. The underlying calculations were produced from fundamental formulae and typically need computer evaluation for full accuracy; tabulated values allow accuracy better than 1%.
• Practical assumptions: The method targets 100% load factor current rating equations and loss calculations for sheaths in double‑circuit flat formations.

Practical applications and who should use it

• Cable designers and manufacturers: To size metallic sheaths, select sheath material (aluminium vs lead), and compute eddy‑current losses needed for thermal and ampacity assessments.
• Power system engineers and utilities: To determine realistic current‑carrying capacities for parallel or adjacent circuits and to assess the impact of sheath bonding practices (single bonding, cross‑bonding, or both‑end bonding).
• Consultants and testing laboratories: For accurate loss estimation in complex cable layouts where mutual sheath eddy currents affect heating and rating.
• Software developers: Implement tabulated coefficients and interpolation routines in cable‑rating and thermal‑analysis tools.

Related standards

• IEC 60287‑1‑1:2023 - Losses and current rating for cables in a single circuit (general).
• IEC 60287‑1‑3 - Calculation method for circulating current losses in double circuits (sheaths bonded at both ends).

Using IEC 60287‑1‑2:2023 ensures consistent, internationally recognized treatment of sheath eddy‑current effects in double‑circuit flat cable formations, improving accuracy of ampacity calculations and informed choices about sheath design and bonding practice.