What is the base AC when not wearing Armor?
Several character classes do not typically or cannot wear armor. Sorcerer, Monk, Wizard, Barbarian. Monk, Barbarian, and even draconian ancestry sorcerer have unarmored defense perks that help boost their AC. But Wizard does not. So what is the wizards unarmored AC?
I suspect it is 10 as everything seems to add to that value in the armor table and in the unarmored defense (except draconian ancestry which seems to give +3 for scales). But I have not been able to find that rule in the PHB.
From the PHB p 14:
Without armor or a shield, your character's AC equals 10 + his or her Dexterity modifier.
Keep in mind that this is simply the default way to calculate AC. Armor and draconian ancestry do not add to this AC, they change the way your whole AC is calculated as is explained on the same page in the PHB and detailed, for example in this answer.