With MA magnetic trip units
In distribution applications, circuit breakers equipped with MA magnetic-only trip
units are used for short-circuit protection of secondary windings of LV/LV transformers with overload protection on the primary side.
Magnetic protection (Im)
Short-circuit protection with an adjustable pick-up Im that initiates instantaneous tripping if exceeded.
Im = In x … set in amps on an adjustment dial covering the range 6 to 14 x In for 2.5 to 100 A ratings or 9 to 14 In for 150
to 220 A ratings.