Ac unit wire and breaker sizing.

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augie47

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Welcome

See no reason you should have failed. I'd ask for a Code reference.
 

infinity

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got fail inspection today for running 10/2 Romex wire on 45 amp breaker.
name plate call for 27.7 amp min circuit amp and 45 amp Max over current protection

If that is why you've failed then your installation is code complaint and the inspector is incorrect.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
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Welcome again.

In other words, you're correct, and the inspector is wrong. You've met both of the parameters specified on the equipment label.

When he mentions Art. 240.4 or 240.4(D) or 240.4(D)(7), you counter (politely) with "read 240.4(D) again and then see 240.4(G)."
 

Little Bill

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Make sure he didn't fail you for the NM (Romex) wiring maybe being in conduit outside. Other wise, your MCA & MOPD are in line with your conductors & breaker.
 
Larry Fine reply ;

Larry Fine reply ;

Welcome again.

In other words, you're correct, and the inspector is wrong. You've met both of the parameters specified on the equipment label.

When he mentions Art. 240.4 or 240.4(D) or 240.4(D)(7), you counter (politely) with "read 240.4(D) again and then see 240.4(G)."


I have been reviewing this same matter over the past few days also referring to an AC unit.. I have read where 240.4(G) refers to 440 parts 3 & 4.. I have read completely threw 440 3 & 4, but could not find the "Specific Permission" to allow the 240.4(D)"small conductor", in this case, #10 for breaker over 30amps.. please name where this "Specific Permission" is within this section, and also, have you had experience with this issue before where an engineer or code specialist had confirmed the matter for you? thank you for your knowledge..
 

Dennis Alwon

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I have been reviewing this same matter over the past few days also referring to an AC unit.. I have read where 240.4(G) refers to 440 parts 3 & 4.. I have read completely threw 440 3 & 4, but could not find the "Specific Permission" to allow the 240.4(D)"small conductor", in this case, #10 for breaker over 30amps.. please name where this "Specific Permission" is within this section, and also, have you had experience with this issue before where an engineer or code specialist had confirmed the matter for you? thank you for your knowledge..

240.4 (G) allows this since the a/c has overload protection which will protect the branch circuit from overload. The breaker is protecting the wire from short circuit and ground fault
 

infinity

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I have been reviewing this same matter over the past few days also referring to an AC unit.. I have read where 240.4(G) refers to 440 parts 3 & 4.. I have read completely threw 440 3 & 4, but could not find the "Specific Permission" to allow the 240.4(D)"small conductor", in this case, #10 for breaker over 30amps.. please name where this "Specific Permission" is within this section, and also, have you had experience with this issue before where an engineer or code specialist had confirmed the matter for you? thank you for your knowledge..

The limits in 240.4(D) do not apply to AC units. The nameplate of the unit gives you the minimum conductor size based on the MCA. You can use an OCPD sized anywhere between the MCA and the MaxOCPD listed on the nameplate. Don't have the book in front of me but someone will fill in the code section.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I have read completely threw 440 3 & 4, but could not find the "Specific Permission" to allow the 240.4(D)"small conductor", in this case, #10 for breaker over 30amps.
It's not specifically called a special permission, but it's allowed by not being prohibited. The breaker is allowed to be large enough to carry starting current.

As stated above, since overload protection is built into the compressor, it need not be covered by the branch circuit's breaker.

As a short-duration event, a #10 wire will carry enough current to trip a 45a breaker during a short circuit. The numbers on the AC label mean the math has already been done.
 

goldstar

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got fail inspection today for running 10/2 Romex wire on 45 amp breaker.
name plate call for 27.7 amp min circuit amp and 45 amp Max over current protection
Sorry, but I seem to be a little dense in following the responses you received on this topic. The nameplate rating states that the minimum OC protection is 27.7 amps but you're protecting it at 45 amps. Irrespective of what other Code sections might state Table 310.15(B)(16) does not allow you to protect # 10 wiring with a 45 amp breaker. This is an AC unit that will probably run for hours at a time. In my mind I would think that the insulation on the # 10 wiring would be severely taxed. Could someone please explain why # 8 would not be required ?

Bear in mind the OP is in NJ and still on the 2014 NEC if that has any bearing.
 
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guschash

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Ohio
meter/disconnect

meter/disconnect

Would a meter/disconnect be considered as being ( or having an external shut off needs ).? Inspector approved it but power company want a external disconnect.
 

Dennis Alwon

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Sorry, but I seem to be a little dense in following the responses you received on this topic. The nameplate rating states that the minimum OC protection is 27.7 amps but you're protecting it at 45 amps. Irrespective of what other Code sections might state Table 310.15(B)(16) does not allow you to protect # 10 wiring with a 45 amp breaker. This is an AC unit that will probably run for hours at a time. In my mind I would think that the insulation on the # 10 wiring would be severely taxed. Could someone please explain why # 8 would not be required ?

Bear in mind the OP is in NJ and still on the 2014 NEC if that has any bearing.

Well, I'll try again. An a/c units has overload protection that protects the branch circuit from overload. The #10 wire will only see a load of more than 30 amps when there is a ground fault or short circuit so the 45 amp breaker will protect the conductors from that.

The #10 will not be seeing 45 amps but rather less than 27.7 amps because that number has 125% built in. The mca on the unit states 45 amp max so you can use the 45 amp breaker. 240.4 G allows us to protect the a/c based on art. 440
 

augie47

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Providing you with a little documentations to support Dennis' post:

The basic rule is in 240.4:
240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected
against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in
240.4(A) through (G).

Note the underlined.. unless permitted in "G"When you look at 240.4(G) you will find a Table that shows Art 440 A/C units.
That is how the Code allows us to not follow the basic rule in 240.4
It takes into consideration that, as Dennis states, the conductor is protected against overload by the A/C overload protection and the breaker must have a rating that allows for the inrush current of the motor.
 

goldstar

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New Jersey
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Thanks Augie & Dennis. The NEC is funny like that. For years you come to rely on table 310.16 for wire amp ratings. Then they change the table # to 310.15(B) and you have to get used to that. Then you have to take into consideration how other sections might modify that table's guidelines. Why can't they make it simple?

Anyway, I think this section sums it up :

440.22 Application and Selection.
(A) Rating or Setting for Individual Motor-Compressor. The motor-compressor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175 percent of the motor-compressor rated-load current or branch-circuit selection current, whichever is greater, shall be permitted, provided that, where the protection specified is not sufficient for the starting current of the motor, the rating or setting shall be permitted to be increased but shall not exceed 225 percent of the motor rated load current or branch-circuit selection current, whichever is greater.

Exception: The rating of the branch-circuit short-circuit and ground-fault protective device shall not be required to be less than 15 amperes.
Why couldn't that have been the answer from the start ?
 

infinity

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Thanks Augie & Dennis. The NEC is funny like that. For years you come to rely on table 310.16 for wire amp ratings. Then they change the table # to 310.15(B) and you have to get used to that. Then you have to take into consideration how other sections might modify that table's guidelines. Why can't they make it simple?

Anyway, I think this section sums it up :

Why couldn't that have been the answer from the start ?

Don't AC units typcially have two motors?
 

goldstar

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New Jersey
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Don't AC units typically have two motors?
If we're considering the cooling fan motor, isn't the condenser motor the largest load which ends up dumping you back to 440.22(A)? If not, what would the correct answer have been if not the section I cited ?
 

Dennis Alwon

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Why couldn't that have been the answer from the start ?

The older heat pumps and a/c units nameplates that I worked on had 175% for the Max overcurrent protective device. For some reason they have improved the units so that the need for a breaker so much larger to help the unit start was not necessary.
 

kwired

Electron manager
Location
NE Nebraska
Thanks Augie & Dennis. The NEC is funny like that. For years you come to rely on table 310.16 for wire amp ratings. Then they change the table # to 310.15(B) and you have to get used to that. Then you have to take into consideration how other sections might modify that table's guidelines. Why can't they make it simple?
Table 310.16 might have a different name today, but is still same table with only minor changes. All it is is minimum ampacity of conductors (per insulation temp rating) and at an ambient of 30 degrees C. Overcurrent protection starts in art 240, general rules require conductors to be protected at no more then their ampacity, but then there is other sections that modify those general rules for specific applications, air conditioning and refrigeration equipment is one of those other sections.

Bottom line is MCA was 27.7, 10 AWG has an ampacity greater than 27.7 and is acceptable, unless maybe adjustments are needed, and the small conductor rule of 240.4(D) doesn't apply to this application because of 240.4(G). Since the unit had MOCP of 45 then that is the limit, had this been a motor and art 430 applied - is possible that 10 AWG could easily be allowed on 60 amp breaker for a motor with similar load rating.
 
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