# well pump



## jkoepke (Feb 17, 2014)

Ok got my well drilled, im running 12 THHN wire from breaker panel 75 feet to well head and then it will be hooked to 200 feet twisted submersible 12 gauge well wire. The pump is a gould 1/2 horse 230 volt 2 wire submersible pump. What size of breaker should i use, 20 amp double pole? Thank You


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## stickboy1375 (Apr 28, 2012)

jkoepke said:


> Ok got my well drilled, im running 12 THHN wire from breaker panel 75 feet to well head and then it will be hooked to 200 feet twisted submersible 12 gauge well wire. The pump is a gould 1/2 horse 230 volt 2 wire submersible pump. What size of breaker should i use, 20 amp double pole? Thank You


15 amp breaker for a 1/2 HP pump.


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## Removeb4flight (May 12, 2013)

A 20 amp breaker is OK for 12 gauge wire. However, the allowable distance for a 1/2 hp motor on 12 gauge is 220 ft, which you are over. See page 179, table 16-1, 43rd addition Wiring Simplified. I would use 10 gauge wire, to avoid excessive voltage drop.


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## stickboy1375 (Apr 28, 2012)

dmclean701 said:


> A 20 amp breaker is OK for 12 gauge wire. However, the allowable distance for a 1/2 hp motor on 12 gauge is 220 ft, which you are over. See page 179, table 16-1, 43rd addition Wiring Simplified. I would use 10 gauge wire, to avoid excessive voltage drop.


Sure, you can use a 20 amp breaker for 12 AWG, BUT.... we are not protecting the conductors with a circuit breaker when dealing with motors, we are only providing ground fault and short circuit protection, and since a 1/2 HP motor draws 4.9 amps x 250% equals 12.25, a 15 amp breaker is the MAXIMUM that is allowed.


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## Removeb4flight (May 12, 2013)

Motors are confusing. Is that table I cited overly conservative for starting voltage drop? Do submersible pump motors have internal over current protection? Just asking.


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## Robpo (Mar 30, 2014)

I have a special place on my meter box for a well pump circuit so I can turn off main and not turn off well. Just thought I would mention it, not sure if it is code.


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## stickboy1375 (Apr 28, 2012)

dmclean701 said:


> Motors are confusing. Is that table I cited overly conservative for starting voltage drop? Do submersible pump motors have internal over current protection? Just asking.


Well pumps contain their own internal protection, and you have to size any pump with the motor tables in the NEC.


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## stickboy1375 (Apr 28, 2012)

Robpo said:


> I have a special place on my meter box for a well pump circuit so I can turn off main and not turn off well. Just thought I would mention it, not sure if it is code.


That's not a common thing where I live, but I believe it's some farmers meter or something, but yes, you are good to go.


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## micromind (Mar 9, 2008)

Here are the figures for this pump. Since it is a 1/2HP 2 wire operating at 230 volts, my Franklin book lists the full-load current at 5.0 amps. The maximum current is 6.0 amps based on the service factor. The actual current will almost certainly be somewhere between these two values. Well pumps typically load motors to the gills.......

Assuming 6 amps and 300' of #12, the voltage drop will be around 7 volts. This means that if the actual service voltage is 240, the motor will be getting 233 volts. This is well within the + / - 10% voltage variation that all NEMA rated motors must meet. 

The locked rotor current (starting current) for this motor is 23 amps. In this case, the motor will be getting 212 volts for starting. There isn't a standard for voltage drop during starting. It is more of an art than a science. All motors are designed to start on less than standard voltage, even fully loaded. 

Since a close-coupled centrifugal pump starts basically no-load, the motor can handle a LOT of voltage drop at starting. I'd bet good money that this motor would start just fine on 175 volts with clear water. If it has minerals and stuff in it, the bearings will load up over time and it'd need a bit more voltage. 

But in this case, the starting voltage is again within the 10% range. 

The figures for #14s in this case would be 11 volts drop running resulting in 229 at the motor and 41 volts drop starting resulting in 199 at the motor. This would be acceptable for this installation. 

In short, #12s would be good, but as noted, (per NEC 430.52), the breaker cannot be larger than 15 amp. 

Rob.


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## jkoepke (Feb 17, 2014)

Thanks for all the replies I will be going with 15 amp.


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