QUICK ANSWER

A current rating is valid under stated conditions. Ambient temperature, grouping and installation method can change the usable rating.

01Start from a defined installation

Ask whether the reference value assumes free air, a tray, a conduit or burial. Record loaded conductors, spacing and ambient conditions. Two current tables with different assumptions cannot establish which supplier has the better cable.

02Apply the relevant corrections

The design calculation should use the applicable method and factors for temperature, grouping and, where relevant, ground conditions. These are not universal percentages. Ask for the assumptions alongside the result, particularly for crowded trays or exposed rooftop routes.

03Coordinate protection and voltage drop

Thermal capacity is one check in a larger selection process. The designer must also review voltage drop, fault withstand and protective-device coordination. A cable that carries the load thermally can still fail a different design requirement.

Before you send an enquiry

  • Describe the installation
  • Record ambient and grouping
  • Request calculation assumptions
  • Review protection and voltage drop
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References & further reading

An introductory buying guide, not a project design or a claim of certification. Confirm current standards, local requirements and the exact product documentation with the designer and supplier.