Accessory H-rail mounting for 4NC52 4NC bushing type current transformer The bushing-type current transformers are used for primary rated currents of 40 A to 3000 A, secondary rated currents of 5 A or 1 A and in the categories 0.2S, 0.5 and 1. They are also suitable for measurement functions with PAC and AI Energy Meter thanks to better accuracy, and are employed in the mechanical engineering sector most commonly for new systems with mid-range power ratings and in plant construction.