This means over load relay senses and reacts to the harmful over load currents only.
From the blue wire a wire goes to the thermal overload relay normally close contacts and from there the wire goes to the contactor coil A1 terminal.
From the red line wire a wire goes to the normally close push button switch.
When the current interrupts the iron core gets demagnetized as a result it releases the armature this breaks the circuit.
The contactor has three main normally open(NO) contacts and auxiliary contact which has lower power ratings and it can be of normally open(NO) or normally closed(NC) type.