Standards are periodically reviewed and updated by technical committees. Implementing obsolete formulas can cause catastrophic design errors.

Protective devices are designed to clear faults quickly. Using IEC 60949, an engineer can calculate the maximum fault current the cable can tolerate. With this value, they can then select a circuit breaker or fuse with a clearing time fast enough to ensure the cable's thermal limit ((I^2t) let-through energy) is never exceeded. This integrated approach ensures seamless and safe protection coordination.

IEC 60949 (1988) defines the calculation of thermally permissible short-circuit currents in cables, accounting for non-adiabatic heating effects to determine maximum allowable fault currents. The standard provides essential formulas to verify cable safety and set protective device timing against insulation damage. Purchase the standard at the IEC Webstore IEC Webstore IEC 60949:1988

You can view uploaded copies and technical breakdowns of the 1988 edition on Scribd .

The standard modifies the classic adiabatic formula to include a correction factor for heat loss. The General Formula

If you are looking for specific formulas or technical details without the full administrative front matter, several reputable technical platforms provide extensive summaries and excerpted calculations:

Utilizing this standard is critical for several aspects of electrical system design: 1. Cable Screen and Armour Sizing

It aims to unify practices among designers by providing a method to incorporate heat transfer into adjacent materials (non-adiabatic effects) rather than assuming no heat loss.

If you are currently working on a cable calculation project, let me know: