a/c overcurrent protection

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johnnyw

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Hi, I failed inpection on a panel changeout,had a 40amp breaker on a 10 wire for an air conditioner circuit. thought it was ok citing 440-22 in code. anybody have info, thanks johnnyw.
 

raider1

Senior Member
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Location
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Welcome to the forum.:)

What was the minimum circuit ampacity marked on the unit?

What was the maximum overcurrent protective device marked on the unit?

440.22 permits you to use the above information for selecting the branch circuit conductors and the branch circuit overcurrent protective device.

Chris
 

raider1

Senior Member
Staff member
Location
Logan, Utah
If the maximum overcurrent protective device rating was 35 amps then a 40 amp breaker would be a violation.

Chris
 

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
I agree with Chris but I don't understand why the nameplate doesn't allow 175%. Since the nameplate states 35 as the maximum OCP then that is what it needs to be. I have noticed more a/c units that are rating the OCPD lower than 175%-- I am not sure where this trend is coming from.
 

david luchini

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Connecticut
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I agree with Chris but I don't understand why the nameplate doesn't allow 175%. Since the nameplate states 35 as the maximum OCP then that is what it needs to be. I have noticed more a/c units that are rating the OCPD lower than 175%-- I am not sure where this trend is coming from.

Dennis, the MOCP is 175% in this case. The MCA is 24.4, so full load is 19.52 (assuming a single motor-compressor.) 175% of 19.52A is 34.16A, or a 35A MOCP.
 

roger

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Fl
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i was under the impression that a forty is the next standard size available, is this true?

35 is a standard rating.

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.

Roger
 

Cow

Senior Member
Location
Eastern Oregon
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Electrician
It definitely helps to check 240.6 on that type of stuff. Just because you never see a certain size breaker doesn't mean the manufacturers don't make them.:)
 

Dennis Alwon

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Retired Electrical Contractor
Dennis, the MOCP is 175% in this case. The MCA is 24.4, so full load is 19.52 (assuming a single motor-compressor.) 175% of 19.52A is 34.16A, or a 35A MOCP.
Help me out here ... art. 440.22 states

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.

Is not the branch circuit selection current 24.4 amps? I take this to be that 175% of the 24.4
 

david luchini

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Location
Connecticut
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Is not the branch circuit selection current 24.4 amps? I take this to be that 175% of the 24.4

No, 24.4 is NOT the "branch circuit selection current." Post #3 says that 24.4 is the "minimum circuit ampacity," which would be determined by 440.32 (or 440.33 or 440.34, etc.)

The branch circuit selection current is only used in specific instances and must be marked on the nameplate per 440.4(C). The way I see it, if there is not a "branch circuit selection current" marked on the unit, then it does not apply.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
No, 24.4 is NOT the "branch circuit selection current." Post #3 says that 24.4 is the "minimum circuit ampacity," which would be determined by 440.32 (or 440.33 or 440.34, etc.)

The branch circuit selection current is only used in specific instances and must be marked on the nameplate per 440.4(C). The way I see it, if there is not a "branch circuit selection current" marked on the unit, then it does not apply.

Is not the 24.4 amps the current we use to determine our branch circuit selection? Maybe I am confused what the branch cir. selection current is.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Is not the 24.4 amps the current we use to determine our branch circuit selection? Maybe I am confused what the branch cir. selection current is.

I agree with you Dennis.

The branch circuit selection current and minimum circuit ampacity are the same thing.

Chris
 

haskindm

Senior Member
Location
Maryland
JohnnyW,
As others have said, 35 amps is a standard size. That said, the label on the unit said MAXIMUM fuse size, so you may not exceed that size. If the label had said something ridiculous like "Maximum fuse or HVACR Circuit Breaker 39 amps" you still would not be able to use a 40-amp fuse, even though it is the next standard size. The permission to go up to the next standard size goes away when the words "MAXIMUM" or "SHALL NOT EXCEED ___" are used. Be careful to read all of the words....
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Is not the 24.4 amps the current we use to determine our branch circuit selection? Maybe I am confused what the branch cir. selection current is.

I agree with you Dennis.

The branch circuit selection current and minimum circuit ampacity are the same thing.

Chris

No, "branch circuit selection current" and "minimum circuit ampacity" are NOT the same thing.

Read the definition of "branch circuit selection current" in the Definitions section 440.2 "The value in amperes to be used instead of the rated-load current...WHEREVER the running overload protective device permits a sustained current greater than the specified percentage of the rated-load current."

Read, also, 440.4(C): "A hermetic refrigerant motor-compressor, or equipment containing such a compressor, having a protection system that is approved for use with the motor-compressor that it protects and that permits a continuous current in excess of the specified percentage of nameplate rated-load current...shall also be marked with a branch-circuit selection current...This marking shall be provided by the equipment manufacturer and shall be on the nameplate where the rated-load current appears."

The "branch-circuit selection current" is specific to equipment that has overload protection that is greater than the specified percentage of rated load current (per 440.52), and the bcsc must be marked on the equipment nameplate by the manufacturer.

This is clearly not the same thing as the minimum circuit ampacity. In fact, per 440.32, the MCA would be 125% of the bcsc if the bcsc is larger than the rated-load current.
 
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