Please Help! Motor Question

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mnandy

Member
I'm studying to take my journeymans test and after going through mikes dvd on motor and air conditioning calculations I found out that I can put a #14 awg wire on a 30 amp breaker thats providing short circuit and ground fault protection, ( I included the motor I used below) because of 240.4 (D) which points me to Table 240.4 (G) which states I go to Article 430 Parts III, IV, V, VI, and VII for specific conductor applications instead of following the rules contained in 240.4 (D) which would have other wise made me go from #14 awg to #10 awg for a 30 ampere breaker. Well in school I brought this up to my instructor and he said no your wrong you cant do that, and you must use #10 awg wire and he pointed to article 240.4 (D) and said basically article 430 points you back to 240.4 (D) to apply that article. I'm not seeing it. I still think I'm right! I dont know why this is bugging me so much but I dont want to go in and take my journeymans test and fail by one percentage point because of this. If I'm right can someone please explain to me an easy way to explain this to him.

here was my motor example:

2HP Motor motor terminals 75 degree c terminals
230V
11A FLA
12FLC

Conductor size: 12x125%= 15A .....so I used 14awg wire rated at 20A
Breaker: 12 FLC x 250%= 30A Breaker
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I did not check your calcs but you are correct. A #14 gauge wire can be installed with a 30 amp breaker. The breaker will give short circuit and ground fault protection. The a/c will have overload protection built in that will protect the conductors from overload.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Your instructor was wrong 240.4(D) doesn't apply to this installation because of the first sentence which says:
240.4(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.

As you noted, 240.4(G) would apply therefore nullifying the restrictions of 240.4(D).
 

cpal

Senior Member
Location
MA
the op was made at 2:45AM ??? EST ???

what code is inforce and why are you loosing sleep.
 

mnandy

Member
No just a regular motor! Thanks for your reply :) Its hard to point these things out when your instructor is so sure hes right and not willing to budge.
 

mnandy

Member
So bottom line I use article 430 Parts III, IV, V, VI, and VII for specific conductor applications for motors and article 240.4 (D) 1-7 does not apply to anything in Table 240.4(G) unless I guess you were pointed back there of course which Ive yet to see so far.

Thank you so much... its tough when people are teaching you that don't exactly understand themselves what there reading. It almost makes a person do twice the work. Its hard to teach an old dog new tricks. :)
 

SegDog

Member
Location
Philadelphia
old dog, old tricks

old dog, old tricks

I, always, add a disclaimer that, "I don't know everything, and I'll be proving that point very shortly."

I've had many good teachers that had gaps in their own training and education. Go gentle on the teacher; a little diplomacy will go a long way.

Dog
 

mnandy

Member
Once again thanks! Update!!!

Once again thanks! Update!!!

I went back and tried to explain my side of how you apply 240.4 (D) and use Table 240.4 (G) to one instructor along with some evidence and an article with illustrations and he basically shut me out and said there is no way you can do this your illustrations are wrong and so is all that other evidence, and no inspector would ever pass that, and you have to use #12 on a 20 Amp breaker. and he pointed back to 240.4 (D). he also said it doesn't specifically say you can do it in Article 430. By the way I'm still sticking with you can put a #14 on a 20 Amp Breaker and you dont apply 240.4 (D) to article 430 and the parts listed in Table 240.4 (G). I also included the article I gave him if anyone would like to check it out. here it is http://ecmweb.com/mag/electric_motor_calculations_part/

The other instructor actually gave me the time of day and actually looked into it with the same stuff I gave the first instructor, but he came to the conclusion that you cant do it either, saying article 430 points you to use table 310.16 and then he points to the asterrisk that points you back to 240.4 (D) and says there thats why you cant.

I know im just an apprentice learning the code and in no way am I trying to say Im smarter than any one of them but it just sucks knowing that its the wrong way and other people in class are going to learn how to do it the wrong way. I know I will never forget how to apply the rules of 240.4 (D) now, by all the stuff ive been through.

Thanks everyone for your help
Andrew :)
 

mnandy

Member
I went back and tried to explain my side of how you apply 240.4 (D) and use Table 240.4 (G) to one instructor along with some evidence and an article with illustrations and he basically shut me out and said there is no way you can do this your illustrations are wrong and so is all that other evidence, and no inspector would ever pass that, and you have to use #12 on a 20 Amp breaker. and he pointed back to 240.4 (D). he also said it doesn't specifically say you can do it in Article 430. By the way I'm still sticking with you can put a #14 on a 20 Amp Breaker and you dont apply 240.4 (D) to article 430 and the parts listed in Table 240.4 (G). I also included the article I gave him if anyone would like to check it out. here it is http://ecmweb.com/mag/electric_motor_calculations_part/

The other instructor actually gave me the time of day and actually looked into it with the same stuff I gave the first instructor, but he came to the conclusion that you cant do it either, saying article 430 points you to use table 310.16 and then he points to the asterrisk that points you back to 240.4 (D) and says there thats why you cant.

I know im just an apprentice learning the code and in no way am I trying to say Im smarter than any one of them but it just sucks knowing that its the wrong way and other people in class are going to learn how to do it the wrong way. I know I will never forget how to apply the rules of 240.4 (D) now, by all the stuff ive been through.

Thanks everyone for your help
Andrew
 

jcole

Senior Member
There are at least two inspectors that I know of that is in the same denial your teachers are mdandy. I have just come to learn to apply 240. 4D to everything just so I dont have to argue with inspectors, teachers, coworkers, etc. no matter how many times I show them the intent of the code. Your teacher will not be the last person you debate this with if you stay in the trade very long.

And to answer your question, you are right.
 
Location
Maine
440.32

440.32

I don't believe you can use awg #14 on a 30 amp brk in this case. 440.32 says conductors must be sized @125% of the larger of the nameplate or OC device.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I went back and tried to explain my side of how you apply 240.4 (D) and use Table 240.4 (G) to one instructor along with some evidence and an article with illustrations and he basically shut me out and said there is no way you can do this your illustrations are wrong and so is all that other evidence, and no inspector would ever pass that, and you have to use #12 on a 20 Amp breaker. and he pointed back to 240.4 (D). he also said it doesn't specifically say you can do it in Article 430. By the way I'm still sticking with you can put a #14 on a 20 Amp Breaker and you dont apply 240.4 (D) to article 430 and the parts listed in Table 240.4 (G). I also included the article I gave him if anyone would like to check it out. here it is http://ecmweb.com/mag/electric_motor_calculations_part/

The other instructor actually gave me the time of day and actually looked into it with the same stuff I gave the first instructor, but he came to the conclusion that you cant do it either, saying article 430 points you to use table 310.16 and then he points to the asterrisk that points you back to 240.4 (D) and says there thats why you cant.

I know im just an apprentice learning the code and in no way am I trying to say Im smarter than any one of them but it just sucks knowing that its the wrong way and other people in class are going to learn how to do it the wrong way. I know I will never forget how to apply the rules of 240.4 (D) now, by all the stuff ive been through.

Thanks everyone for your help
Andrew :)

Point out the first sentence of 240.4(D).

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(G) specifcally says that motor and motor control circuit conductors shall be permitted to have there overcurrent devices sized in accordance with 430 Parts III, IV, V, VI, VII.

Chris
 

mnandy

Member
There are at least two inspectors that I know of that is in the same denial your teachers are mdandy. I have just come to learn to apply 240. 4D to everything just so I dont have to argue with inspectors, teachers, coworkers, etc. no matter how many times I show them the intent of the code. Your teacher will not be the last person you debate this with if you stay in the trade very long.

And to answer your question, you are right.

Thanks thats why sometimes I think its almost easier to study the code at home by myself with out other influences trying to form my opinion for me. But on the other hand I learn a lot from them too. Maybe if they acknowledged they were wrong that would mean they have to accept they've been teaching this article wrong for years. Could that be why they wont accept it? Oh well what do you do. In the grand scheme of things its not that big of a deal. It sure taught me how stubborn people can be.

Andrew
 

tom baker

First Chief Moderator
Staff member
Mike Holt has several graphics that show a #14 wire on 30A OCPD.
I have an information sheet that walks one thru how the rules apply.
PM me if you want a copy.
 

cpal

Senior Member
Location
MA
I don't believe you can use awg #14 on a 30 amp brk in this case. 440.32 says conductors must be sized @125% of the larger of the nameplate or OC device.

Dan I do not see the term ocpd in that section it mentions branch circuit selection current.

440.2 Definitions.
Branch-Circuit Selection Current. The value in amperes to be used instead of the rated-load current in determining the ratings of motor branch-circuit conductors, disconnecting means, controllers, and branch-circuit short-circuit and ground-fault protective devices wherever the running overload protective device permits a sustained current greater than the specified percentage of the rated-load current. The value of branch-circuit selection current will always be equal to or greater than the marked rated-load current.


That value is used to size the short circuit protection.
 

dana1028

Senior Member
...and said there is no way you can do this your illustrations are wrong and so is all that other evidence, and no inspector would ever pass that ... Thanks everyone for your help
Andrew :)

Unfortunately he is pretty close about the inspectors; after all, he's the instructor and he's teaching it wrong, can you imagine how off base the inspectors are?

I don't mean to slight any inspectors here, as I are one:D, but my experience shows very few inspectors are real savvy on this stuff.
 
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