Short Circuit Rating: Earth Screen Fault Capacity for AS/NZS 1972 Type 2S XLPE Cables
A Type 2S 3.3kV XLPE mining cable with a 3×95mm² conductor cross-section has two completely independent short circuit ratings: the phase conductor short circuit rating of approximately 13.6 kiloamperes (meaning the three phase conductors can withstand a three-phase symmetrical fault current of 13.6 kA for up to one second before reaching their 250°C thermal limit), and the earth screen fault capacity of approximately 5.0 kiloamperes (meaning the individual copper or copper-alloy screening layer surrounding each phase conductor can safely conduct a phase-to-earth fault current of 5.0 kA for the duration of a protective relay response, typically 50–100 milliseconds). These two ratings are not alternatives or overlapping specifications—they describe different physical paths through which fault current flows, different insulation stress scenarios, and different design objectives. Understanding why these two ratings exist, how they differ, and how they interact with mine protection systems is essential for any electrical engineer designing or specifying cable systems in underground coal mines.
