Motor Minimum OCPD For Commercial Applications

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djr3203

Member
Location
San Francisco
For a commercial applications, does NEC allow 20A CB to be a minimum OCPD size for motors? Or if I have a small motor, do I have to use 15A CB to comply with the maximum 2.5x the FLA rule?

Thanks for the help all!

DJR
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
For a commercial applications, does NEC allow 20A CB to be a minimum OCPD size for motors? Or if I have a small motor, do I have to use 15A CB to comply with the maximum 2.5x the FLA rule?

Thanks for the help all!

DJR

The food allows you to use the next standard size cb above 250%.
 

iwire

Moderator
Staff member
Location
Massachusetts
For a commercial applications, does NEC allow 20A CB to be a minimum OCPD size for motors? Or if I have a small motor, do I have to use 15A CB to comply with the maximum 2.5x the FLA rule?

Thanks for the help all!

DJR

That depends on the motor

Ii apears you believe 15 amp circuits are not allowed in commercial space.
 

djr3203

Member
Location
San Francisco
??????

Example, 1HP, 460V, 3PH motor has an FLA=2.1. Maximum OCPD (inverse time CB) = 2.5*2.1 = 5.25A. Do I have to use a 15A CB or is there a rule that allows me to use 20A CB to protect this motor?

Petersona, "The food allows you to use the next standard size cb above 250%." ????

iwire, why does it appear I don't think 15A is allowed on commercial jobs? I just want to know if there is a rule that allows me to use 20A CB instead. I am pretty sure there is somewhere in the NEC that allows a minimum 20A CB to be used on commercial projects for receptacle branch circuits. I typically only see 20A CB on commercial projects, but I currently have a project with mixed breakers, and I want to confirm what the exact rule is when it comes to protecting motors.


 

iwire

Moderator
Staff member
Location
Massachusetts
??????

Example, 1HP, 460V, 3PH motor has an FLA=2.1. Maximum OCPD (inverse time CB) = 2.5*2.1 = 5.25A. Do I have to use a 15A CB or is there a rule that allows me to use 20A CB to protect this motor?

What do you think the word maximum means?


iwire, why does it appear I don't think 15A is allowed on commercial jobs? I just want to know if there is a rule that allows me to use 20A CB instead. I am pretty sure there is somewhere in the NEC that allows a minimum 20A CB to be used on commercial projects for receptacle branch circuits.

I think that because 1) your posts seem to indicate you do not want to use a 15 amp breaker. 2) because you just confirmed that.

There is no NEC rule requiring 20 amp circuits in commercial.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I would suggest that you look at Part IV of Article 430. Specifically 430.52 for an individual motor circuit and 430.53 for several motors or loads on one branch circuit.

There are lots of variables to your initial question.

Chris
 

djr3203

Member
Location
San Francisco
No, my post did not just confirm that. This is frustrating... I was just asking if there was a rule that allowed for a 20A CB installation in lieu of a 15A CB. I really don't understand why everyone feels the need to blurt out ridiculous comments to be "cute". Isn't this a professional forum?

And I know what maximum means (rude comment); however, the NEC loves to stipulate something in one section and override it in another. Just because one section says maximum, doesn't necessarily mean that is not changed elsewhere.

Don't worry guys I found my answers on another site with helpful posts. Turns out certain municipalities in the US don't allow 15Amp breakers in commercial applications.

[h=1][/h]
 

victor.cherkashi

Senior Member
Location
NYC, NY
??????

Example, 1HP, 460V, 3PH motor has an FLA=2.1. Maximum OCPD (inverse time CB) = 2.5*2.1 = 5.25A. Do I have to use a 15A CB or is there a rule that allows me to use 20A CB to protect this motor?

Petersona, "The food allows you to use the next standard size cb above 250%." ????

iwire, why does it appear I don't think 15A is allowed on commercial jobs? I just want to know if there is a rule that allows me to use 20A CB instead. I am pretty sure there is somewhere in the NEC that allows a minimum 20A CB to be used on commercial projects for receptacle branch circuits. I typically only see 20A CB on commercial projects, but I currently have a project with mixed breakers, and I want to confirm what the exact rule is when it comes to protecting motors.


As I know with above motors you have two options: 1. Use 5A fuse with 5A cabling. 2. Use 15A fuse/CB with 10AWG wiring. Note: in any case you must have overload protection for motor. 5A or 15A are just protection for cabling between fuse and overload protection of motor.

Sent from my Nexus 5 using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
As I know with above motors you have two options: 1. Use 5A fuse with 5A cabling. 2. Use 15A fuse/CB with 10AWG wiring. Note: in any case you must have overload protection for motor. 5A or 15A are just protection for cabling between fuse and overload protection of motor.

Sent from my Nexus 5 using Tapatalk

The code does not require you use smaller than a fifteen amp cb.

The size of the conductors is determined by the required ampacity, not the rating of the cb.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
No, my post did not just confirm that. This is frustrating... I was just asking if there was a rule that allowed for a 20A CB installation in lieu of a 15A CB. I really don't understand why everyone feels the need to blurt out ridiculous comments to be "cute". Isn't this a professional forum?

And I know what maximum means (rude comment); however, the NEC loves to stipulate something in one section and override it in another. Just because one section says maximum, doesn't necessarily mean that is not changed elsewhere.
Can you cite specific NEC sections that override other NEC sections?
Don't worry guys I found my answers on another site with helpful posts. Turns out certain municipalities in the US don't allow 15Amp breakers in commercial applications.
While there are many areas that adopt the NEC with changes, the NEC does not permit that. Your question asked about the NEC. When a question is asked about the NEC, you will get comments based on that document as published by the NFPA, not as modified by various adopting agencies.

I would also like to see the exact modification that was made to say that minimum OCPD is 20 amps. Was it written and placed in the code in a location that would make it apply to the rules found in Article 430? A couple rules like that that I am aware of were placed in Article 210 and have no effect on the rules in Article 430.
 

Smart $

Esteemed Member
Location
Ohio
...
I would also like to see the exact modification that was made to say that minimum OCPD is 20 amps. Was it written and placed in the code in a location that would make it apply to the rules found in Article 430? A couple rules like that that I am aware of were placed in Article 210 and have no effect on the rules in Article 430.

... Turns out certain municipalities in the US don't allow 15Amp breakers in commercial applications.
You best get the "in writing" version of that from the AHJ before you go off half cocked thinking you know it all now. :happyyes:


BTW... welcome to the forum :thumbsup:
 
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