With warmer weather approaching the topic of breaker and wire sizing has come up a few times recently.

The Circuit Breaker is there to protect the wire only, not the appliance!!!!!
Therefore the breaker MUST be matched to the wires minimum amperage capacity.
Maximum Overcurrent Protection = Circuit Breaker size in amps
Minimum Circuit Ampacity = Minimum Wire gauge allowed
 
The yellow line is the Maximum Circuit Breaker size.
The red line is the  Minimum wire ampacity
So we need to size the breaker based on the wire minimum ampacity
The following are generally followed for solid copper wire ( Romex)
14/2 wire rated 15 amps
12/2 wire rated for 20 amps
10/2 wire rated for 30 amps
8/2 rated for 40 amps
6/2 rated for 55 amps 
LOCAL NEC CODES MUST BE FOLLOWED 
 
Let’s look at an RA1330,
Maximum Breaker Size is 30 amps.
Minimum wire capacity is 18 amps....so
You can use a 20 amp circuit breaker with 12/2 Romex as 12/2 wire is rated for 20 amps.
Always remember THE BREAKER IS THERE TO PROTECT THE WIRE NOT THE APPLIANCE !!!
You can always oversize the wire , if using a 20 DPST breaker you can use 10/2 if needed...however...
YOU CAN NEVER OVERSIZE THE CIRCUIT BREAKER !!!