ummmm sorry but what is the full form of NEC here? Notional Electrical Code?
People learning the trades like electricians aren’t expected to perform any more than the most basic calculations. For example, for a given current draw, cable length and conduit characteristics, an electrician in training might be asked to look to a table to determine the appropriate wire gauge. How this table was derived is outside the scope of an entry-level electrician’s training. It’s good to be curious but an instructor has a curriculum to maintain and must keep to schedule. A student can independently study the hows and whys but it sounds like this is beyond what’s being taught in your class.
Hi again. Maybe you’re interested in learning more about PCB. You may enjoy PCB designing and making PCB at home. That will help clear many basic topics learnt in class. You may become interested in this write-up:
https://pcbtracks.com/basics-of-pcb-des … beginners/
It discusses all matters related to PCB design easily.