25 amp dual pole breaker on 12/2 wire

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Jim Goodman

JEG in Raleigh
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I have a new 230V 1 hp, 10 gpm Grudfos pump that was just installed and set at 300'. My old pump was a 3/4 hp, 8 gpm pump, also set at 300'. The old pump never delivered enough volume. The electrician who wired the house ran 12/2 wire to energize the 3/4 hp pump, and it had a 20 amp dual pole breaker. The new pump calls for a 25 amp breaker. I have the 12/2 wire running from the panel, 110' out to the well, then 8/2 wire running 300' down the well to the pump. Grundfos has instructions on their website on how to determine if the wiring is adequate for the pump when you have mixed gauges of wire being used. Based on those calculations, I am very safe with the 110' of 12/2 wire connecting to the 8/2 wire. But, the NEC says the maximum breaker size for 12 gauge wire is 20 amps. I have installed the 25 amp breaker that Grundfos says is necessary, and according to the manual, the pumps maximum load is 9.8 amps, and if I add a 30% safety factor, the load would be 12.75 amps....well within the limits of the 12 gauge wire. It's a long story that I'll skip, but I cannot get a new wire into my panel. But, I have a remote meter base and could run heavier gauge wire from a panel on the meter base to that to a sub-panel by the well. There are other issues that would need to be addressed if that sub-panel were to be installed (connecting the pump with this new wiring setup to my whole-house back-up generator is one of them, and a big one). Bottom line is for the electrical work and trenching for the sub-panel, the cost is coming in around $5000. I'm already blown out of the water with the nearly $5000 I've already spent on the new pump and really can't afford another $5000 for the electrical work. So my question is, am I OK (from a fire safety standpoint) using the 25 amp breaker with my 110' of 12 gauge wire? I have been searching the web for info and on an electrician's forum, I have read several people saying that with an HVAC system, you can use the 25 amp breaker and be perfectly safe, even though that is not allowed in the current NEC. At this point, I'm not really concerned about being in compliance with the letter of the 2017 code.....I just want to make sure I'm not going to burn my house down. I've read the NEC is very conservative and the 20 amp breaker maximum is based on that 20 amps being 80% of the capacity of the 12 gauge wire. I also read that the 20 amp maximum in the NEC is a somewhat recent addition, and that it did not used to be the case. Any help would be greatly appreciated.
 

Reach4

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It is likely that a regular 20 amp breaker would not blow. There are some breakers designed to be more tolerant of high initial loads. https://www.schneider-electric.us/en/product-range/7229-square-d™-qo™-and-qob-miniature-circuit-breakers/7080560902-(hm)-high-magnetic-circuit-breakers/ The QO-HM breakers are an example. Obviously you would need a breaker that your box can use, and we don't know what breakers your box uses.

I would not expect a 25 amp breaker to cause a fire. They might run 30 amps through 12 gauge in an automobile, if the voltage drop is not a problem to the load.

I am not a pro.
 
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