100A panel feed #1 vs. #3 debate

T have distributor datasheets for cable. I still use the Graybar or McDonald's (RIP)sheets and notice different types of insulation. If I make my choice, I go for the biggest.

I rather see it myself than hear it say from somebody, because when the inspector comes somebody in trouble will be me. This question is like frying eggs in teflon coated pan or not.

I'll assume that you are in North America and you are referring to AWG ratings in your descriptions.

But where the heck are you getting your information? There is no #3 AWG building wire available commercially, so if you are reading off of a chart from a wire manufacturer it is meaningless. The only thing that counts is the NEC table that pertains to the specific installation requirements you must follow for your situation. Above ground, free air, underground, in raceway, how many conductors with it, voltage drop over distance etc. etc. etc. all contribute to which ampacity table you must use. Get yourself a copy of the NEC and look through the myriad of charts in Article 310.

→ British Standard 7671.