How are terminal blocks depicted in a wiring diagram?
In my experience, and what is the format in several CAD packages I have used is something similar to the following, for the schematic view you have the following:



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Above the Terminal Blocks are the circles, label TB1:9 through TB1:14 on the right. Which stands for Terminal Block (Strip) 1 - Terminal 9 through Terminal 14.

And usually there is a Terminal Block Overview which would look similar to this:



Source : Link

Which depicts a three level terminal block, and the wires (cables) connected on each side, and where those cable go.

These are certainly not the only ways, but is common to several CAE Systems I have used.