PLC wiring (1) – Wiring of switches, lights, and actuators to a PLC

Here, in this section, we will look into the connection (wiring) of input devices (switches) and output devices (lights and actuators) to the PLC. Sinking and sourcing are two important terms in PLC wiring. They are used to describe the direction of the conventional current flow between two circuits or devices. A conventional current always flows from positive potential (+) to negative potential (-). Anytime you have a current flowing between two devices, one will be sourcing while the other will be sinking.

The sourcing device is the device that provides the current (positive), while the sinking device is the device that absorbs the current (that is, the device connected to negative or ground).

In PLC wiring, the two devices in question are input devices and input modules or output devices and output modules. PLC manufacturers usually produce input/output modules that you can either sink or source. There...