In planning your circuit layout, you must differentiate between operating voltage, input voltage, and output voltage.
The operating voltage feeds the internal logic of the individual I/O bases. (Abbreviations: L+ / M- for direct current; L1 / N for alternating current.)
The input voltage supplies the sensors. (Abbreviations, where the leading numbers specify the groups: 1L+ / 1M-, 2L+ / 2M-, ... for direct current; 1L1 / 1N, 2L1 / 2N, ... for alternating current.)
The output voltage drives the actuators. (Abbreviations equivalent to those for input voltage.)
Common Reference Potential
When two or more circuits have a common reference potential (i.e., they are not isolated), their corresponding reference conductors are abbreviated identically– for example, L+ / M- and 1L+ / M- are used when L+ and 1L+ are not isolated.
