6/3 nm cable for stove

[kwired]

I believe the OP had several things rolling around in his head...one of which was if the appliance doesn't need 40A, and it is on a 40A circuit, is the appliance being properly protected. The breaker isn't there to protect the appliance -- the breaker is there to protect the wiring.

210.21(B)(4) says you can use the table for a range.
210.23(C) specifically allows 40 and 50 amp branch circuits to supply cooking appliances. You still need to run a 40 or 50 amp conductor other than the allowed tap conductors at the appliance which normally is the conductors factory installed in the flex conduit whip that comes with the appliance. If you want to run a lesser circuit where the appliance has lesser rating that is allowed with proper OCP to go with whatever conductor you ran.

Bottom line, these appliances are designed to be on up to a 50 amp protected circuit. You can put an oven and a cooktop on a 50 amp circuit together. Not many do but it is permitted.

Information in post 60 also applies.