# New Motor, Ckt Breaker to Use...



## cdnelectrician (Mar 14, 2008)

You can size a circuit breaker to a maximum of 250 % of the FLA of the motor. Sounds like the breaker can't handle the start up current. If the motor is going to be left un-attended you will also need an overload.


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## Traveler 45C (Dec 11, 2009)

The motor won't be unattended. 

Are you saying that a 30a breaker will do the trick? Is there a certain type of breaker I should use for this application? Do breakers have diferent surge current ratings and if so, what do I need?

Will Home Depot have what I need?


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## John Valdes (May 17, 2007)

Use a 30 amp inverse time breaker. (common breaker). See Article 430.52 NEC.


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## Bob Badger (Apr 19, 2009)

cdnelectrician said:


> If the motor is going to be left un-attended you will also need an overload.





Traveler 45C said:


> The motor won't be unattended.


Under the NEC all motors require some sort of OL protection.


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## AussieApprentice (Aug 16, 2008)

cdnelectrician said:


> You can size a circuit breaker to a maximum of 250 % of the FLA of the motor.


I don't know your codes but I assume that you would have to size the cable to 250% FLA if you were going to do that?


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## Old Spark (Nov 18, 2008)

A motor typically draws 6 times the fla inrush current at start up. I've found that a breaker about 1/2 the inrush current can handle the start-up. 250% is going to be the minimum required to keep the breaker from tripping at start up. No you do not size the wire at 250%. You will size the wire at 125% of the fla. This will save you at lot of unnecessary cost vs. sizeing the wire and conduit at 250%. I suggest you purchase a book on electrical motor and controls, or at least get an ugly's. There are charts in them to give you all the info you need.
David


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## AussieApprentice (Aug 16, 2008)

David Channell said:


> No you do not size the wire at 250%. You will size the wire at 125% of the fla.


If you size the wire at 125% and put a breaker at 250% aren't you leaving the cabling unprotected? We would not be allowed to do that here?


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## cdnelectrician (Mar 14, 2008)

AussieApprentice said:


> If you size the wire at 125% and put a breaker at 250% aren't you leaving the cabling unprotected? We would not be allowed to do that here?


 
In that case, the overloads would protect the wire. If you had to size the wire at 250% for every installation it would be way too costly. 

In our code, any motor rated at 1HP or less that is always attended while in operation and that does not have branch circuit overcurrent protection above 15 Amps does not need overload protection.


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## cdnelectrician (Mar 14, 2008)

Traveler 45C said:


> Hello. I'm new to this forum, sought you guys out because I've got a question I'm hoping someone on here can help me with. I'm not an electrician, I'm an electronics tech. I live in Pensacola, Fl.
> 
> I've got to design a ckt to power a 1HP, 115v single phase motor, 1725rpm's that pulls 78amps at start up with a full-load draw of 12.2a. It pops the 20a breaker that I tried to run it on. The motor is powering an oil change pump.
> 
> ...


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## Traveler 45C (Dec 11, 2009)

I got the specs from the manufacturers Spec Sheet.

I bought a 40a breaker, I'll test it later today.


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## electures (Oct 23, 2008)

Branch circuit conductors = #14 AWG.
Inverse Time CB = 40 A
If motor fails to start and run the ITCB can increased to 60A.

Good luck!


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## John Valdes (May 17, 2007)

electures said:


> Branch circuit conductors = #14 AWG.
> Inverse Time CB = 40 A
> If motor fails to start and run the ITCB can increased to 60A.
> 
> Good luck!


You are pushing the limits of Art 430.52 with a 40 amp breaker. You cannot use a 60 amp breaker on a 12.2 amp motor. In fact I would have gone with 30 first. You are pushing the envelope on the wire too. I would use #12.

12.2 X 2.50 = 30.5 (Breaker)
12.2 x 1.25 = 15.25 (Wire)


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## Traveler 45C (Dec 11, 2009)

I used a 40a and the motor worked fine, no binding, sounded smooth. 


I'll also give a 30a breaker a try before I permanently install the motor.


Thanks All!


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## electures (Oct 23, 2008)

John Valdes said:


> You are pushing the limits of Art 430.52 with a 40 amp breaker. You cannot use a 60 amp breaker on a 12.2 amp motor. In fact I would have gone with 30 first. You are pushing the envelope on the wire too. I would use #12.
> 
> 12.2 X 2.50 = 30.5 (Breaker)
> 12.2 x 1.25 = 15.25 (Wire)


Everything I stated is code compliant. If a contractor wired the motor as I stated, I as the EI would have to accept it. Imagine if it was a pool filter motor. It would still be compliant.


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## John Valdes (May 17, 2007)

Traveler 45C said:


> I used a 40a and the motor worked fine, no binding, sounded smooth.
> 
> 
> I'll also give a 30a breaker a try before I permanently install the motor.
> ...


A 40 amp breaker is the maximum. Don't worry about trying a 30 amp. There is no need. :thumbsup:



electures said:


> Everything I stated is code compliant. If a contractor wired the motor as I stated, I as the EI would have to accept it. Imagine if it was a pool filter motor. It would still be compliant.


I did not say you were not compliant. I only said you were pushing the envelope. Since both values can be increased to the next standard size, you are close, thats all. I agree with you. :thumbsup: Except on the 60 amp breaker. You cannot use it. That would exceed 250%.


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## electures (Oct 23, 2008)

John Valdes said:


> A 40 amp breaker is the maximum. Don't worry about trying a 30 amp. There is no need. :thumbsup:
> 
> 
> 
> I did not say you were not compliant. I only said you were pushing the envelope. Since both values can be increased to the next standard size, you are close, thats all. I agree with you. :thumbsup: *Except on the 60 amp breaker. You cannot use it. That would exceed 250%*.


Hi John,

430.52(C)(1) Exception 2(c) states;


_(c) The rating of an inverse time circuit breaker shall_
_be permitted to be increased but shall in no case exceed_
_400 percent for full-load currents of 100 amperes or less or_​_300 percent for full-load currents greater than 100 amperes._

400% of 16A is 64A. Since it in no case can exceed 400% it must be rounded down to a 60A ITCB. And the BC conductors are #14 AWG.


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## John Valdes (May 17, 2007)

electures said:


> Hi John,
> 
> 430.52(C)(1) Exception 2(c) states;
> 
> ...


I did not know that. Thanks for the heads up. I learned something today!


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## electures (Oct 23, 2008)

John Valdes said:


> I did not know that. Thanks for the heads up. I learned something today!


Hi John,

One of the mistakes people make is sizing the BC conductors based on the nameplate FLA. I actually use this motor scenario to teach sizing pool filter motors to inspectors and contractors. It is code compliant to run #14 AWG BC conductors to a 1 HP 115V single phase filter motor. *The only difference is that the EGC has to be #12. *

The following is copied from a handout I use for teaching this;

Motors​*430.6(A) 1* states;
*(1) Table Values. **Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for multispeed motors, the values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate*. Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary. Motors built for low speeds (less than 1200 RPM) or high torques may have higher full-load currents, and multispeed motors will have full-load current varying with speed, in which case the nameplate current ratings shall be used.

Table 430.248 indicates 16 amps for a 115V 1HP single phase motor.

*430.22(A) General* states;

*(A) General. *Conductors that supply a single motor used in a continuous duty application shall have an ampacity of
not less than *125 percent of the motor’s full-load current rating as determined by 430.6(A)(1).*

16A x 125% = 20A

Table 310.16 indicates #14AWG is rate for 20A.

Now before you get your panties in a bunch the asterisk refers us to the bottom of Table 310.16 where it states: *See 240.4(D).* 

240.4(D) states;

*(D) Small Conductors. *Unless *specifically permitted* in 240.4(E) or *(G)*, the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.

240.4(E) refers to tap conductors which is not applicable here. However, 240.4(G) is a table and tells us that Article 430 applies for motor branch circuit conductors. *This means that #14 AWG is specifically permitted to be used for conductors supplying this 20A motor load. *

Next we look at sizing the ground fault, short circuit, overcurrent protective device.

430.52 states;

*430.52 Rating or Setting for Individual Motor Circuit.*
*(A) General. *The motor branch-circuit short-circuit and ground-fault protective device shall comply with 430.52(B) and either 430.52(C) or (D), as applicable.

*(C) Rating or Setting.*
*(1) In Accordance with Table 430.52. *A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430.52 shall be used. (Also read the exception.)

Table 430.52 states that for an inverse time circuit breaker protecting a single phase motor it is to be sized at 250% of the FLA as stated in Table 430.248.

16A x 250% = 40A

Based on the above calculation a 40A ITCB is correct.

If the motor fails to start and run then 430.52(C) (1) Exception No. 2(c) can be applied which states;

_(c) The rating of an inverse time circuit breaker shall be permitted to be increased *but shall in no case exceed 400 percent for full-load currents of 100 amperes or less* or 300 percent for full-load currents greater than 100 amperes._

_16A x 400% = 64A_

_Since we can’t exceed 400% of the motor FLA we round down to a 60A ITCB on a piece of #14 AWG conductor._

_*The real kicker is that if this was a pool filter motor it is code compliant.*_

_Merry Christmas and enjoy the holiday season!!_

_Kevin_


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## Traveler 45C (Dec 11, 2009)

Wow, I didn't know there was so much involved in sizing a breaker. Thanks so much, I've learned alot!


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## Traveler 45C (Dec 11, 2009)

What is a soft start and do I need one for this application?


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## electures (Oct 23, 2008)

Traveler 45C said:


> What is a soft start and do I need one for this application?


A soft start is used to reduce the starting current of the motor. I VFD will also accomplish this. I don't think a 1 HP motor needs this.

L8R,

Kevin


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## John Valdes (May 17, 2007)

Traveler 45C said:


> What is a soft start and do I need one for this application?


No. They do not make soft starts for single phase motors. But they do make soft starts for 3 phase fractional HP motors. When comparing cost, the use of NEMA starters can make soft starts economical.
A NEMA 1 starter cost's more than some small soft starts. That includes soft starts with built in bypass. Soft starters are no longer just for big motors and loads.
Check these. http://www.weg.net/files/products/WEG-ssw-05-soft-starter-usassw05-brochure-english.pdf

Note: I am not affiliated with Weg Electric.


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## Traveler 45C (Dec 11, 2009)

Thanks guys!

I got an off topic question, I don't think it's worth starting a new thread so I'll just ask: Is it harmful to a breaker (magnetic type) to use it as an On/Off switch? It's the breaker for my water heater on my boat. I shut it down when I'm not aboard, a few times per week. I was thinking that I'd install a cut-off switch if I'm gonna' wear out the breaker.

Kevin, where at in Jersey are ya'?

I was born in Newark, lived in Hillside 'till 6th grade then moved down the shore to Waretown. High School in New Egypt (Allentown HS). Left for the Navy in '81 and been gone ever since. Would love to come back but I hear it's kind of expensive to live up there...


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## Old Spark (Nov 18, 2008)

Does the breaker have an SW on it? They make switch rated breakers that will hold up to being used as a switch. Was this factory installed or owner installed system?


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## Traveler 45C (Dec 11, 2009)

No, the water heater ckt has a plain old breaker, OEM.


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## Old Spark (Nov 18, 2008)

Then is probably will not last too long being used as a switch.


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## electures (Oct 23, 2008)

Traveler 45C said:


> Thanks guys!
> 
> I got an off topic question, I don't think it's worth starting a new thread so I'll just ask: Is it harmful to a breaker (magnetic type) to use it as an On/Off switch? It's the breaker for my water heater on my boat. I shut it down when I'm not aboard, a few times per week. I was thinking that I'd install a cut-off switch if I'm gonna' wear out the breaker.
> 
> ...


Turnersville. Fiften minutes from Phila. And yes the cost of living is killing us. My taxes are $7000.00 and climbing.


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## Traveler 45C (Dec 11, 2009)

Sorry to hear that!


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