(57) This unit comprises a box-like body associable, side by side, with electric switches
and selective safety means adapted to avoid unintentional errors in coupling and including
rod-like guide elements (3,3a) protruding from the coupling wall (1a) of said unit
and intended to be inserted within corresponding cavities (4,4′) in the body of the
switch (2). The rod-like elements (3,3a) have a constant transverse cross section
while the corresponding cavities (4,4′) provided in the body of the switch have such
dimensions and depth as to allow the complete insertion of said rod-like elements
only when the nominal currents of the switch are equal or lower than those of the
unit. In particular, the cavities (4) provided in a high nominal current switch have
a portion (4a) with smaller transverse cross section than the inlet portion (4b),
so as to prevent the complete insertion of said rod-like elements (3) if the nominal
current of the differential unit is lower than that of the switch.
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