Three-wire control gets its name from the number of control circuit conductors that must be extended to the switching location from the motor-starter location.
The ungrounded fused supply conductor supplies the series switches with fused, continuous power.
The interconnecting return conductor between the Start and Stop PB switches supplies continuous power to the line side of the NO auxiliary contacts on the motor-starter power contactor through the NC Stop PB switch.
The switch-leg return conductor from the load side of the PB Start switch connects to the load side of the motor-starter NO auxiliary contacts in order to place the two in parallel.
A single wire is then run from this common connection through the NC overload contacts to the line side of the motor-starter solenoid coil.
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