I agree the code teaches derating, but in real world practice I have seen many ignore it. I mean you would have to run multiple conduits for simple things like wall outlets ect. Matter of fact in code class many working electricains were just as shocked as I was by how much you must derate. Looking backwards at that point I saw several projects not derated admittley out of my own ignorance, the wire fill for conduit is useless when you cross it with the derating table, your wires are rated down so much long before the fill is reached (when dealing with smaller conductors #14-10#).
That said on any future designs I will derate for safetys sake!, but I to tryed explaining this to my boss and it was just easyer to run 2" emt and stuff it full. Sorry guys but thats what happened and does happen. Like I say I now know better.
Also running seperate conduit for control wiring is like pulling teeth.
When I talk about control wiring I mean, from thermostat to relays and so on, I know its good to put them in a seperate conduit yet..., I work commercail, radio, tv, broadcast stations, better yet run the suckers in the open much quicker if below 60 volts throw them across that false ceiling. Strap them to the outside on the emt along with the cat 5 ! Ha Ha Ha.
Ive seen 2" emt stuffed with 30 wires no derating.
Like I say the fill tables are a joke, if you derate why would you fill that conduit up? You would not. Run 10 3/4" pipes instead that way you can have 3-6 wires in a stick. Ha Ha would'nt that look nice. And remember you can not use conduit to support conduit! Those 10 pipes be hanging all over the place!
Little off the wall tonight but you get the idea, about what a shock these derating tables are.