HVAC Equipment Circuit (MCA / MOCP)
The minimum circuit ampacity and maximum overcurrent device for a condenser or heat pump per NEC 440.33 / 440.22.
Example
You enter
- Compressor RLA (A) 20
- Condenser-fan FLA (A) 1.5
- Installed breaker (A, optional) 35
You get
- Minimum circuit ampacity (MCA) 26.5 A
- Max overcurrent (MOCP, 175%) 35 A
- Hard-start ceiling (225%) 45 A
- Min conductor (A) 26.5
Details, formula, and sources
MCA is 125% of the compressor RLA plus the other loads, MOCP is 175% to the next standard size down (225% to start) -- with a check of the installed breaker against the nameplate maximum.
MCA = 1.25 x largest motor RLA + sum of the other loads (NEC 440.33). MOCP = 1.75 x largest RLA + others, taken to the next NEC 240.6(A) standard size DOWN (NEC 440.22(A)); the 225% value is the ceiling allowed only where the 175% size will not start the equipment.
NEC 2023 (NFPA 70). Section 440.33 (MCA), 440.22(A) (MOCP), and 240.6(A) (standard device sizes).
Free read-only access at nfpa.org/freeaccess.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: compressor_rla_A, fan_fla_A, installed_breaker_A, mca_A, mocp_A, mocp_max_A, min_conductor_A
- RLA basis the largest motor's rated-load amps (RLA), not locked-rotor amps (LRA); the compressor is normally the largestNEC 440.33
- MOCP rounding 175% is a ceiling, so the device is the largest NEC 240.6(A) standard size not exceeding it (round down); 225% only if needed to startNEC 440.22(A)
- Conductor the branch-circuit conductor ampacity must be at least the MCANEC 440.32 / 440.33