Basic House Wiring -Connections and Code It is rated as able to carry up to 15 amps of current. 12-gauge wire is the next size larger and is allowed to carry up to 20 amps. As a result, the amp rating of a circuit breaker has the following relation to the wire size that has been chosen. A 20-amp breaker is never* allowed to run any circuit whose wires (anywhere on the circuit) are 14 Matching Wire Size to Circuit Amperage - The Spruce If you've shopped for electrical wire, you have likely noticed that there are many types and sizes of wire to choose from. Different types of wire are intended for different uses, but with any of these wire types, knowing the right wire size, or gauge, is key to making the right choice.