The recommended wire gauge for a 30 amp circuit breaker varies slightly depending on the source, but most agree that 10-gauge wire is the minimum size required. However, some sources recommend using 8-gauge wire instead, especially if the circuit will be carrying a continuous load that approaches the maximum capacity of the breaker. Its important to note that the wire size is not the only factor to consider when installing a new circuit or upgrading an old one. The length of the wire and the appliances or devices that will be connected to the circuit also need to be taken into account.