Wire gauge, breaker size and cord/plug matching for appliance circuits

The breaker protects the wire, not the appliance. The NEC caps overcurrent protection for small copper conductors: 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG (lower for aluminum), except where the code specifically allows otherwise (motor and some equipment rules).

Larger appliance circuits follow the ampacity tables: 40 A circuits commonly use 8 AWG copper and 50 A circuits 6 AWG copper. Range cords are sold in 40 A and 50 A versions that reflect the conductor size; both may use the same 14-50 style cap, so read the cord rating, not just the plug.

NEMA receptacle families tell you the wiring: 5-15/5-20 are 120 V with ground; 10-30 and 10-50 are 3-wire 125/250 V with no separate ground (older dryer/range style, existing installs only); 14-30 and 14-50 are 4-wire 125/250 V with ground. On a 14-30 the neutral slot is L-shaped; on a 14-50 it is straight.

The cord must match the receptacle, the appliance terminal block and the circuit. A dryer cord for a 30 A circuit is typically four No. 10 copper conductors (SRD/SRDT type) on a 14-30 plug; the manufacturer sets the minimum length and type.

Aluminum branch-circuit wiring (common in some homes built roughly 1965-1973) has a documented fire history at connections. CPSC recommends specific repair methods; standard devices are not the fix. Treat any warm, discolored aluminum connection as an electrician referral.