Control box design tools/spreadsheets

I am planning a CNC gantry machine and I have decided to use a 2 mesa cards. In addition to the mesa cards, I would need to add:
Power supplies
Safety relays for estop
Relays for switching VFDS and other equipment
Breakers for dust removal/other higher HP equipment
Indicator lights
switches etc
I am planning to use din rail mounted equipment

In my experience so far with control boxes, building is the easy part, and documenting the system is the hard part. I have searched around for good software, but I could not find any open source software available. Perhaps the best way to document the control box would be a spreadsheet. How have others documented their control box? I have seen some really elaborate cnc conversions, and I cannot imagine it was all done on paper or by winging it. If you have some elaborate spreadsheet for the control box design – please share. If you have used other software – please share.

Much appreciated!

Hi JT,

Would you be able to share a screenshot of your document? In this case picture is worth a thousand words.

SP