Hard-Wired Control

Prior to PLCs, many of these control tasks were solved with
contactor or relay controls. This is often referred to as hardwired
control. Circuit diagrams had to be designed, electrical
components specified and installed, and wiring lists created.
Electricians would then wire the components necessary to
perform a specific task. If an error was made, the wires had
to be reconnected correctly. A change in function or system
expansion required extensive component changes and rewiring.