This is for a lawn irrigation sprinkler system. I am changing out to a new pump and need to verify the amp rating of the double pole breaker I need to use to deliver 115 volts to each leg of the motor. The FLA of the motor is 10.9 amps. will a 20 amp be too light and be tripping and or should I use a 30 amp rated CB?
Table 430.52(C)(1) says 250% for inverse time circuit breaker, using Table 430.248 at 8.0A for 1 hp resulting in 20A inverse time breaker. If unable to start the motor without tripping then 430.52(C)(1)(b)(3) allows increasing the breaker up to 400%, so 30A could be allowed.
Minimum wire size needs to be 125% of nameplate applied to Table 310.16, #14 will be minimum size, larger wire would be needed for long distances.
Proper overload protection must also be provided.
You need to look at the motor nameplate and instructions. Really.
Right on there it will state a minimum circuit ampacity and a maximum circuit breaker. You need to pick a breaker size in that range. I.e. it might be min 12.8A max 25A. So a 15A breaker will suffice. If you're that worried about it nuisance tripping, use the max.
A 30A is not legal unless it says so. And yes, 25A is a standard size. Actually it's a correct size for 4500W water heaters.
If the labeling is silent, then you go over to NEC Article 430, but it's unlikely for UL to approve a motor without that data.
Generally when a motor has a wide gap between minimum ampacity and maximum breaker, it is because the motor has overload protection on the motor, thus the breaker size does not need to be a precise match.