Making the Connection with Schematic Diagrams

Many of topics that our students struggle with the most have some level of abstraction. Reading a schematic diagram is near the top of the list. A schematic diagram is a symbolic representation of an abstraction – circuit logic. Mentally tying this symbolic representation to the physical components and wires can be a struggle for some students. This is especially true for devices like contactors and relays that are represented by multiple symbols because they have parts with different functions located in different circuits. Recently I have tried having students draw a schematic diagram of a basic packaged air conditioning system. Then I give them a pictorial diagram with drawings of components and ask them to “wire up” their schematic. Most students have a few difficulties drawing the schematic, but they usually make it past this part without too many scuff marks. The trouble comes when they have to translate the schematic diagram that they drew into “wires” on the pictorial diagram. I believe this is because students can essentially copy circuits they see in the book without understanding the details. However, details are important. Several years ago, we would put all our electrical theory up front. Students did not do any wiring until after covering all the theory. However, I noticed that many students who could draw a basic heat pump schematic diagram could not wire a toggle switch and a light. This caused me to wonder how much they really understood. Having students “wire” units on paper by drawing lines between pictures or drawings of components allows them to work out the connection between the abstract and the physical without burning up all your transformers. I am not suggesting that drawing lines to represent wires replaces wiring actual components, but it will quickly show you who has a clue and who doesn’t. You need to work some more with the folks who can’t differentiate between low voltage and line voltage circuits, or the people who want to put L1 on one side of a spst switch and L2 on the other side of the same switch. The pictorial diagrams with all the wires drawn in can look a bit messy and hard to follow. Using color coded markers helps. Better yet, use colored pencils that can be erased. Use two colors for line voltage and two more for low voltage. Have them draw in large dots where two wires are supposed to connect and little humps where two wires cross that are not supposed to connect. It does not take students long to figure out that neatness is its own reward. Loopy, hastily scribbled lines make for difficult circuit tracing and lead to confusion. I usually have a big stack of pages with the components that need to be “wired up.”