Wiring Diagrams
Wiring Diagrams are often associated with electrical work but it is very important as an Instrumentation Apprentice to have the ability to read a simple wire diagram.
Wiring diagrams are a big part of trade school. You will be looking at simple stop start circuits (See Below) or even something like motor starters. You will be expected to read wiring diagrams and then wire up that same circuit.
As you can see on our first line, we are energizing CR-1. CR means control relay. A control relay has two different kinds of contacts. Normally Closed and Normally Open. When we energize the control relay the Normally Close will open and the Normally Open will close. When a contact is open electricity cannot pass, only when a contact is closed can electricity continue through it.
For example, looking at our diagram we can see that our control relay is not active. This means that our light should be on and our motor should be off. If we press start then the motor will start and our light will turn off.
Wiring Diagrams are also important when installing switches to a plc such as a float switch in the diagram below. When the float reaches its limit, the contact will close and allow the 110VAC to reach the PLC. The PLC receiving the 110VAC signal knows that the float is active and can use that for logic such as starting up a sump pump.
Conclusion
Finally, the understanding of how to read and wire according to a wiring diagram is invaluable for troubleshooting. I use wire diagrams all the time when I am testing PLC input/output or if im testing electrical components such as relays or switches.
