# Breaker recommendation for 1hp well pump



## Daniel Holzman (Mar 10, 2009)

NEC standards are intended to protect the wire, not the pump. Since you have 10 gauge wire, by NEC you can use a 30A breaker or smaller, since 10 gauge copper wire can carry 30A. When I have an electrical installation, I generally follow manufacturer recommendations, as long as the recommendation is NEC compliant.


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## micromind (Mar 9, 2008)

According to code, the largest breaker size allowed for a 1 HP motor operating at 230 volts is 20 amp. 

If you'd like the code reference, I'll post it after I get home from work today.

Rob.


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## bluesboy54 (Oct 12, 2017)

Thank you for your reply.

Yes, please send me a private email and I will reply with my gmail address ... so that you can send me the code.


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## Fishbulb28 (Jul 8, 2016)

You can either leave the 30A or install a 25A.

Since you've already sized the conductors to 10 gauge you may consider this a standard branch circuit. 30A is permissible for this size.

Or you may consider this a motor circuit. The NEC permits the circuit overcurrent device to be sized up to 250% of the full load current for a single phase motor. 250% of 9.1 amps is 22.75 amps. Rounding up to the next standard breaker size is 25 amps. Normally you would use the motor circuit rules to allow much smaller conductors than would be expected. But in your case you've already upsized to 10 gauge due to the long run so there's not any advantage to using motor circuit rules.

In no case would I consider installing the 20 amp breaker. The motor locked rotor amps is already at 21.7A. Due to the long run, voltage drop at motor startup is going to be at 10% or so. This will cause the motor startup time to be a little longer than it would normally be. A 20A breaker would likely not trip during the normal short startup period, but you may get nuisance trips during the longer startup time.


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## bluesboy54 (Oct 12, 2017)

Thank you, very much, for your detailed response.

The 10 gauge wire has a current carrying limit of 30A (maybe a little less for the 500 feet total length). Accordingly, the 10 gauge wire in the well pump circuit allows up to a 30A (total) load. So, the breaker should be sized to the pump load.

Sizing the breaker to exceed the 21.7 amp locked-rotor current makes sense but that could result in the motor burning out before the breaker trips.

Sizing the breaker to 250% the 9.1A full load current makes sense but I am not sure if applying that scaling factor is appropriate.

So, the cases favoring either 25A or 30A to minimize pump motor damage or failure are not compelling, i.e., I still don't understand which breaker rating is most likely to prevent damage to the motor, given the motor begins to operate at higher current due to early stage mechanical or electrical failure.


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## Daniel Holzman (Mar 10, 2009)

The current carrying capacity of the wire has nothing to do with the length of the run, it is strictly controlled by the size of the wire and the insulation type. For typical THHN copper wire, you can carry 30A with #10 wire. Voltage drop is a function of current and length of wire, so you may need to use larger wire to prevent excessive voltage drop, but you do not reduce the allowable current capacity of wire just because you have a long run.

As to the breaker protecting the motor, that is not the purpose of the breaker, it is there to protect the wires. Your motor is protected by the motor starter and internal parts of the motor, not the breaker. If you use too small a breaker in an effort to protect the motor against overcurrent conditions, you will prevent the motor from starting by causing a breaker trip on startup.


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## bluesboy54 (Oct 12, 2017)

Thanks for your reply.

The 10 gauge wire will carry 30A and the motor doesn't rely on the panel breaker. With that understanding I will leave the 30A breaker we installed in place.


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## micromind (Mar 9, 2008)

Here are the code references.

430.6(A)(1)......The values given in tables 430.247, 248, 248 and 249 shall be used to determine the ampacity of conductors or amp ratings of switches, branch circuit short-circuit and ground-fault protection instead of nameplate values.

Table 430.248 lists a 1 HP single phase motor operating at 230 volts as 8 amps. 

430.52(A). The motor branch circuit short-circuit and ground-fault protective device shall comply with 430.52(B), 430.52(C) or 430.52(D) as applicable. 

430.52(C)(1). A protective device that has a rating not exceeding the value calculated according to table 430.52 shall be used. Exception #1 allows the next larger size to be used if it's not a standard value but in no case larger than 400%. 

Table 430.52 lists an inverse time breaker (basic standard breaker) as 250%.

8 amps (from table 430.248) X 250% (from Table 430.52) = 20 amps. This is the largest breaker allowed by code. The only exception would be if the breaker trips before the motor gets up to speed.


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## bluesboy54 (Oct 12, 2017)

Thanks for the specification. From the NEC specification provided I understand the following ...

According to the manufacturer the M10422 current will increase from full load (FL) of 7.9A to service factor full load (SFFL) of 9.1A, after about a year of normal operation.

The standard 430.52 specifies 250% inverse breaker time for a standard breaker. According to 430.52 the breaker rating should be no greater than 2.5 x 9.1A = 22.75A. 430.52 exception 1 allows to increase the breaker size to the next common rating, in this case 25A.

To be compliant with NEC 430.52 I should replace the 30A breaker with a 25A breaker.


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## micromind (Mar 9, 2008)

430.6(A)(1) states that the values in the tables shall be used unless the motor is rated at less than 1200 RPM, is a high-torque type or is multi-speed. 

The nameplate current cannot be used to size the breaker. 

If I were installing this pump, I would use a 15 amp breaker and in fact have done so for 6 1HP single phase submersible pump motors over the last 27 years (that I can remember). 

Even though the code maximum breaker size in this case is 20 amps, I have seen a lot more than one that has a 30 amp breaker........

The actual reality is that any breaker from 15 to 30 will work just fine and also will protect the circuit.


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## bluesboy54 (Oct 12, 2017)

The M10422 pump rotates at 3450rpm so 430.52 applies.

I assume a 20A to 30A breaker are fine but if it were my pump I would install a 25A breaker, as per 430.52. I respect the NEC (and all other) data based standards, i.e., standards are created from analysis of performance and life test data. My intuition or experience is not equivalent to data based standards ;-)

MANY thanks to all forum members that responded to my request for guidance. As above, I now have a much appreciated data based recommendation to make to my father-in-law.


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## micromind (Mar 9, 2008)

A 25 amp breaker is in violation of 430.52. 20 amp is the largest size allowed. 

But a 25 will be perfectly fine from a safety and operational standpoint though.


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## bluesboy54 (Oct 12, 2017)

430.52 stipulates that the breaker rating = 2.5 x operating current

In a previous post you reference 430.248 that stipulates a 1 HP single phase motor operating at 230 volts as 8 amps. For the case of a 1hp/230V/8A motor the recommended breaker rating is 20A (2.5 x 8A = 20A).

The Goulds model M10422, according to the manufacturer, will, after approximately one year, operate at its SFFL current of 9.1A. Accordingly, for the case of a M10422 the recommended breaker rating is 25A (2.5 x 9.1A = 22.75A ... the next highest standard breaker is 25A, as allowed by Exception #1).


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## micromind (Mar 9, 2008)

430.6(A)(1) stipulates that the table values are to be used, not the nameplate values.

Code requirements overrule manufacturers recommendations.


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## bluesboy54 (Oct 12, 2017)

Which NEC standard is the standard for specifying the breaker to protect a motor operating (not including start up) at current values above SFFL?


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## micromind (Mar 9, 2008)

The breaker that supplies the motor circuit doesn't protect the motor or the wire. It exists only for short-circuit and ground-fault protection. 

430.32(B) states that any motor 1 HP or smaller shall be protected from overloads by one of the following means. Then it goes on to specify a separate O/L or one built in to the motor. 

430.6(A)(2) states that a separate O/L is to be sized based on the nameplate current (not the table values). 

This will protect the motor and the wire from damage due to overloads and failure to start (locked rotor). This is also why the breaker can often be larger than the wire. 

Service factor enters the equation only by the O/L manufacturers heater or setting tables, not by code. Most manufacturers will specify a smaller heater element or a lower setting if the SF is 1.0


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## bluesboy54 (Oct 12, 2017)

I am going to call Goulds Technical for their recommendation for overload protection for the M10422.

No need for further discussion in this forum.

Thanks to all.


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