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?
3 Answers
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.
answered Jun 12 at 0:32
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.
answered Jun 12 at 0:43
Harper - Reinstate MonicaHarper - Reinstate Monica
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15 amps double pole breaker is the size you want.
Larger breakers might cause more damage to the pump if there is a problem.
15 amp breaker must use 14 gauge wire at the minimum, but larger gauge wire is allowed and recommended for large distances(~plus 100 feet) to reduce voltage drop.
