For reasons irrelevant to my question, I’ve been looking at the 100A subpanel in my house and noticed that my electric oven (which the manufacturer says needs 40A circuit) is on a 30A breaker. After briefly panicking that my oven was on an undersized circuit, I popped the panel cover off and measured the wire to be #8 wire (the wiring was redone by the house flippers we bought from and the sheathing is black too, while the dryer lines are #10 and orange sheathing). So it seems that the wiring is indeed the correct 40A circuit. Phew. I assume that they just found it easier to buy a box of 30A breakers and use them for the three 30A+ circuits in the panel.
So here’s my question: for $12 should I go down to the hardware store and pickup a 40A breaker for this circuit so that it is properly sized? In the year we’ve lived in this house the oven has never tripped the breaker, so maybe I should just leave it. Is there a standard way to mark that the circuit really is #8 wire so a future electrician/home inspector/future owner doesn’t also freak out?
Relatedly, the breaker in the subpanel itself is 200A, even though the breaker at the main panel is 100A. How much should I worry about that? In the event of pulling >100 many amps, the main panel breaker should trip and protect the circuit, so maybe that’s also fine? That feeder line is also the biggest wire I’ve ever seen in my life so maybe the wiring is sized for 200A?