Branch circuit selection current, MCA

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electricg

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Location
wa
Is Branch circuit selection current the same as MCA? I believe MCA stands for maximum continuous amps, or is it minimum circuit ampacity? . This is what I am reading on a name plate.
 

david luchini

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Is Branch circuit selection current the same as MCA? I believe MCA stands for maximum continuous amps, or is it minimum circuit ampacity? . This is what I am reading on a name plate.

No, branch circuit selection current and MCA are not the same thing.

MCA is minimum circuit ampacity. See 440.32 and 440.33 for determination of minimum circuit ampacity.

Branch circuit selection current (where it exists) is used to determine the MCA.
 

olc

Senior Member
Minimum size of the circuit (conductors) for the inverter type heat pump below?
240V
HP_1 electric1024_1.jpg
 

bwat

EE
Location
NC
Occupation
EE
Conductors need to be rated for at least 17.1 amps... fuse can be a maximum of 20A.

So something like #12 and a 20A fuse.
 

don_resqcapt19

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Illinois
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retired electrician
I have never seen a nameplate that includes the branch circuit selection current and it is totally different from the MCA. The following is from the UL Marking Guide for Air Conditioning equipment.
14. BRANCH-CIRCUIT SELECTION CURRENT
The nameplate on a unit that includes a hermetic refrigerant motor-compressor may show
branch-circuit selection current for the motor-compressor in accordance with NEC® Section
440.4(C). This rating may be identified by a suitable abbreviation and will always be equal to or
higher than the motor-compressor RLA rating marked on the unit nameplate. The branch-circuit
selection current rating for the motor-compressor is to be used instead of the rated-load amperes
in determining appropriate ratings for externally mounted controllers and disconnecting means,
branch-circuit conductors, and short-circuit and ground-fault protective devices for these
conductors. A branch-circuit selection current rating is always included on the unit nameplate if
the motor-compressor’s thermal protector or the protective system built into the unit permits a
continuous current flow greater than 156 percent of the rated-load current for the motorcompressor,
or the single overall ampere rating for the unit marked on the unit nameplate (see
“Electrical Load Ratings”).
Equipment that has a branch circuit selection current has an internal overload device that operates at a current greater than 140% but less than 156% of the rated compressor current.
Equipment that has an MCA has an internal overload that operates at or less than 140% of the rated compressor current.
 

olc

Senior Member
Every time I have checked in the past, The MCA is (1.25 X the compressor RLA) plus the condenser fan FLA.
Obviously not the case above.
Here is what the manufacturer says:
Inverter systems do not use a calculation to determine MCA – its determined by actual measurements of the internal control valve. Note also that MCA values are reviewed with Intertek when the equipment is evaluated for UL 1995 compliance.
 
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