8 AWG copper.
A #14 wire will do fine for grounding a 20 amp device. That is the size of the ground wire in a 2 conductor # 12 wire building cable.
The size of the ground wire for a circuit is typically based on the size of the circuit breaker protecting that circuit. For a 200 amp circuit breaker, the recommended ground wire size is 4/0 AWG (American Wire Gauge) copper wire. This wire size helps ensure that the ground wire can safely carry any fault currents that may occur in the electrical system.
On a 30 amp circuit, you would use a #10 copper ground. The ground never has to be larger than the ungrounded conductors.
A 14 gauge wire is typically used on a 15 amp circuit breaker. It is not recommended to use a larger circuit breaker with a smaller wire size as this can create a fire hazard.
AWG # 10 wire on 30 amp circuit.
The recommended wire size for a 30 amp circuit is typically 10 gauge wire.
The recommended wire size for a 60 amp circuit is typically 6-gauge wire.
The appropriate wire size for a 20 amp circuit is typically 12-gauge wire.
For a 25 amp circuit, the appropriate wire size is typically 10 gauge wire.
The appropriate wire size for a 30 amp circuit is typically 10 gauge wire.
The appropriate wire size for a 50 amp circuit is typically 6-gauge wire.
The appropriate wire size for a 60 amp circuit is typically 6-gauge wire.
The recommended wire size for a 20 amp circuit is typically 12-gauge wire.
The recommended wire size for a 35 amp circuit is typically 10 gauge wire.
The recommended wire size for a 50 amp circuit is typically 6-gauge wire.
The recommended wire size for a 220v 20 amp circuit is typically 12-gauge wire.
The recommended wire size for a 220v 30 amp circuit is typically 10 gauge wire.