It is a great help to have the same number on both ends of each wire.
I once had to trouble shoot a machine where each wire had a different number on each end.
All the terminals had unique numbers.
The wires were numbered according to the terminal to which they were connected.
So a wire between terminal 4 and terminal 27 would have a 4 on one end and a 27 on the other end.
I can only guess that it was so they could hire barely literate workers to assemble the panels.
Trouble shooting was challenging!
I arranged my circuits into ladder diagrams.
The line were numbered sequentially.
Line #1 would be numbered thus:
The wire from line one to the first device would be #10,
The wire from the first device to the second device would be #11,
So, any wire number from 10 to 19 would be in line 1 of the ladder diagram.
Any wire from 20 to 29 would be in the second line of the ladder diagram, etc.
Then, under each set of relay contacts was the line number of the relay coil controlling those contacts.
And down the right hand side of the ladder diagram would be a series of numbers beside each relay coil, indicating in which lines were contacts controlled by that relay.
I was on holiday in Vancouver when I received a call from a refinery in Toronto.
A PLC panel that I had designed had gone down and locked up.
It was an obscure program bug.
Thanks to the numbering system I was able to follow the diagram over tha phone and draw enough of the diagram to find the trouble and suggest a temporary fix.
I never could have done it without the index numbers.
Bill
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"Why not the best?"
Jimmy Carter