HVAC Wire Size, MCA and Breaker (MOCP) Sizing
Enter the compressor RLA and the other loads to see the minimum circuit ampacity (MCA), the maximum breaker (MOCP) and the minimum copper wire size. The calculator needs JavaScript; the tables are below. No account, nothing to install.
NEC Wire Gauge / MCA / MOCP
MCA = 1.25 × Compressor RLA + Other FLAs (NEC 440.32)
The calculator box needs JavaScript. MCA = 1.25 x compressor RLA + other FLAs, rounded to 0.1 A. MOCP = 1.75 x compressor RLA + other FLAs, then the first standard breaker size at or above it. The wire size is read from the MCA on the ladder below.
Assumptions: 75°C copper conductors, ≤3 current-carrying conductors in raceway, standard 30°C ambient basis (NEC Table 310.16 & 440.22).
Verify against the equipment's own nameplate MCA/MOCP if listed — nameplate always wins. Check local code.
Wire size ladder
| MCA | Est. min copper wire |
|---|---|
| Up to 15 A | 14 AWG |
| Up to 20 A | 12 AWG |
| Up to 30 A | 10 AWG |
| Up to 40 A | 8 AWG |
| Up to 55 A | 6 AWG |
| Up to 70 A | 4 AWG |
| Over 70 A | 3 AWG or larger |
Standard breaker sizes used: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200 A.
MCA, breaker and wire by compressor RLA
Each cell is MCA in amps, then the MOCP breaker size in amps, then the minimum copper wire size, for the compressor RLA in the first column and the other loads (fan, pump) shown at the top. Assumptions: 75°C copper conductors, ≤3 current-carrying conductors in raceway, standard 30°C ambient basis (NEC Table 310.16 & 440.22). Check local code.
| Compressor RLA (A) | Other FLAs 0 A: MCA / breaker / wire | Other FLAs 2 A: MCA / breaker / wire | Other FLAs 5 A: MCA / breaker / wire |
|---|---|---|---|
| 5 | 6.3 A / 15 A / 14 AWG | 8.3 A / 15 A / 14 AWG | 11.3 A / 15 A / 14 AWG |
| 6 | 7.5 A / 15 A / 14 AWG | 9.5 A / 15 A / 14 AWG | 12.5 A / 20 A / 14 AWG |
| 7 | 8.8 A / 15 A / 14 AWG | 10.8 A / 15 A / 14 AWG | 13.8 A / 20 A / 14 AWG |
| 8 | 10 A / 15 A / 14 AWG | 12 A / 20 A / 14 AWG | 15 A / 20 A / 14 AWG |
| 9 | 11.3 A / 20 A / 14 AWG | 13.3 A / 20 A / 14 AWG | 16.3 A / 25 A / 12 AWG |
| 10 | 12.5 A / 20 A / 14 AWG | 14.5 A / 20 A / 14 AWG | 17.5 A / 25 A / 12 AWG |
| 11 | 13.8 A / 20 A / 14 AWG | 15.8 A / 25 A / 12 AWG | 18.8 A / 25 A / 12 AWG |
| 12 | 15 A / 25 A / 14 AWG | 17 A / 25 A / 12 AWG | 20 A / 30 A / 12 AWG |
| 13 | 16.3 A / 25 A / 12 AWG | 18.3 A / 25 A / 12 AWG | 21.3 A / 30 A / 10 AWG |
| 14 | 17.5 A / 25 A / 12 AWG | 19.5 A / 30 A / 12 AWG | 22.5 A / 30 A / 10 AWG |
| 15 | 18.8 A / 30 A / 12 AWG | 20.8 A / 30 A / 10 AWG | 23.8 A / 35 A / 10 AWG |
| 16 | 20 A / 30 A / 12 AWG | 22 A / 30 A / 10 AWG | 25 A / 35 A / 10 AWG |
| 17 | 21.3 A / 30 A / 10 AWG | 23.3 A / 35 A / 10 AWG | 26.3 A / 35 A / 10 AWG |
| 18 | 22.5 A / 35 A / 10 AWG | 24.5 A / 35 A / 10 AWG | 27.5 A / 40 A / 10 AWG |
| 19 | 23.8 A / 35 A / 10 AWG | 25.8 A / 40 A / 10 AWG | 28.8 A / 40 A / 10 AWG |
| 20 | 25 A / 35 A / 10 AWG | 27 A / 40 A / 10 AWG | 30 A / 40 A / 10 AWG |
| 21 | 26.3 A / 40 A / 10 AWG | 28.3 A / 40 A / 10 AWG | 31.3 A / 45 A / 8 AWG |
| 22 | 27.5 A / 40 A / 10 AWG | 29.5 A / 45 A / 10 AWG | 32.5 A / 45 A / 8 AWG |
| 23 | 28.8 A / 45 A / 10 AWG | 30.8 A / 45 A / 8 AWG | 33.8 A / 50 A / 8 AWG |
| 24 | 30 A / 45 A / 10 AWG | 32 A / 45 A / 8 AWG | 35 A / 50 A / 8 AWG |
| 25 | 31.3 A / 45 A / 8 AWG | 33.3 A / 50 A / 8 AWG | 36.3 A / 50 A / 8 AWG |
| 26 | 32.5 A / 50 A / 8 AWG | 34.5 A / 50 A / 8 AWG | 37.5 A / 60 A / 8 AWG |
| 27 | 33.8 A / 50 A / 8 AWG | 35.8 A / 50 A / 8 AWG | 38.8 A / 60 A / 8 AWG |
| 28 | 35 A / 50 A / 8 AWG | 37 A / 60 A / 8 AWG | 40 A / 60 A / 8 AWG |
| 29 | 36.3 A / 60 A / 8 AWG | 38.3 A / 60 A / 8 AWG | 41.3 A / 60 A / 6 AWG |
| 30 | 37.5 A / 60 A / 8 AWG | 39.5 A / 60 A / 8 AWG | 42.5 A / 60 A / 6 AWG |
| 31 | 38.8 A / 60 A / 8 AWG | 40.8 A / 60 A / 6 AWG | 43.8 A / 60 A / 6 AWG |
| 32 | 40 A / 60 A / 8 AWG | 42 A / 60 A / 6 AWG | 45 A / 70 A / 6 AWG |
| 33 | 41.3 A / 60 A / 6 AWG | 43.3 A / 60 A / 6 AWG | 46.3 A / 70 A / 6 AWG |
| 34 | 42.5 A / 60 A / 6 AWG | 44.5 A / 70 A / 6 AWG | 47.5 A / 70 A / 6 AWG |
| 35 | 43.8 A / 70 A / 6 AWG | 45.8 A / 70 A / 6 AWG | 48.8 A / 70 A / 6 AWG |
| 36 | 45 A / 70 A / 6 AWG | 47 A / 70 A / 6 AWG | 50 A / 70 A / 6 AWG |
| 37 | 46.3 A / 70 A / 6 AWG | 48.3 A / 70 A / 6 AWG | 51.3 A / 70 A / 6 AWG |
| 38 | 47.5 A / 70 A / 6 AWG | 49.5 A / 70 A / 6 AWG | 52.5 A / 80 A / 6 AWG |
| 39 | 48.8 A / 70 A / 6 AWG | 50.8 A / 80 A / 6 AWG | 53.8 A / 80 A / 6 AWG |
| 40 | 50 A / 70 A / 6 AWG | 52 A / 80 A / 6 AWG | 55 A / 80 A / 6 AWG |
| 41 | 51.3 A / 80 A / 6 AWG | 53.3 A / 80 A / 6 AWG | 56.3 A / 80 A / 4 AWG |
| 42 | 52.5 A / 80 A / 6 AWG | 54.5 A / 80 A / 6 AWG | 57.5 A / 80 A / 4 AWG |
| 43 | 53.8 A / 80 A / 6 AWG | 55.8 A / 80 A / 4 AWG | 58.8 A / 90 A / 4 AWG |
| 44 | 55 A / 80 A / 6 AWG | 57 A / 80 A / 4 AWG | 60 A / 90 A / 4 AWG |
| 45 | 56.3 A / 80 A / 4 AWG | 58.3 A / 90 A / 4 AWG | 61.3 A / 90 A / 4 AWG |
| 46 | 57.5 A / 90 A / 4 AWG | 59.5 A / 90 A / 4 AWG | 62.5 A / 90 A / 4 AWG |
| 47 | 58.8 A / 90 A / 4 AWG | 60.8 A / 90 A / 4 AWG | 63.8 A / 90 A / 4 AWG |
| 48 | 60 A / 90 A / 4 AWG | 62 A / 90 A / 4 AWG | 65 A / 90 A / 4 AWG |
| 49 | 61.3 A / 90 A / 4 AWG | 63.3 A / 90 A / 4 AWG | 66.3 A / 100 A / 4 AWG |
| 50 | 62.5 A / 90 A / 4 AWG | 64.5 A / 90 A / 4 AWG | 67.5 A / 100 A / 4 AWG |
| 51 | 63.8 A / 90 A / 4 AWG | 65.8 A / 100 A / 4 AWG | 68.8 A / 100 A / 4 AWG |
| 52 | 65 A / 100 A / 4 AWG | 67 A / 100 A / 4 AWG | 70 A / 100 A / 4 AWG |
| 53 | 66.3 A / 100 A / 4 AWG | 68.3 A / 100 A / 4 AWG | 71.3 A / 100 A / 3 AWG or larger |
| 54 | 67.5 A / 100 A / 4 AWG | 69.5 A / 100 A / 4 AWG | 72.5 A / 100 A / 3 AWG or larger |
| 55 | 68.8 A / 100 A / 4 AWG | 70.8 A / 100 A / 3 AWG or larger | 73.8 A / 110 A / 3 AWG or larger |
| 56 | 70 A / 100 A / 4 AWG | 72 A / 100 A / 3 AWG or larger | 75 A / 110 A / 3 AWG or larger |
| 57 | 71.3 A / 100 A / 3 AWG or larger | 73.3 A / 110 A / 3 AWG or larger | 76.3 A / 110 A / 3 AWG or larger |
| 58 | 72.5 A / 110 A / 3 AWG or larger | 74.5 A / 110 A / 3 AWG or larger | 77.5 A / 110 A / 3 AWG or larger |
| 59 | 73.8 A / 110 A / 3 AWG or larger | 75.8 A / 110 A / 3 AWG or larger | 78.8 A / 110 A / 3 AWG or larger |
| 60 | 75 A / 110 A / 3 AWG or larger | 77 A / 110 A / 3 AWG or larger | 80 A / 110 A / 3 AWG or larger |
Frequently asked questions
What is MCA on an HVAC nameplate?
MCA is the minimum circuit ampacity: the smallest current rating the supply wiring to the unit must have. This page works it out as 1.25 times the compressor RLA plus the other full-load amps (fan, pump), the rule the Equipment Tracker app uses (NEC 440.32). If the equipment nameplate lists an MCA, the nameplate value is the one to use.
What is MOCP and how is the breaker size picked?
MOCP is the maximum overcurrent protection: the largest breaker or fuse the unit may be on. This page takes 1.75 times the compressor RLA plus the other full-load amps and then picks the first standard breaker size at or above that number. The standard sizes on the page are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175 and 200 amps. If the nameplate lists a maximum breaker size, use the nameplate.
What wire size does the page give for a given MCA?
It reads the MCA against a ladder of copper wire sizes: up to 15 A is 14 AWG, up to 20 A is 12 AWG, up to 30 A is 10 AWG, up to 40 A is 8 AWG, up to 55 A is 6 AWG, up to 70 A is 4 AWG, and above 70 A the page says 3 AWG or larger. It is an estimate of the minimum copper wire size, not a design.
What does this page assume?
Copper conductors rated 75 degrees C, no more than three current-carrying conductors in the raceway, and a standard 30 degrees C ambient (the basis of NEC Table 310.16 and 440.22). Aluminum wire, a hotter ambient, more conductors in the conduit, long runs and voltage drop all change the answer and are not covered. Check local code and the equipment nameplate.
Does the nameplate override this page?
Yes. If the equipment lists its own MCA and maximum breaker size on the nameplate, the nameplate always wins. This page is a quick reference for when you only have the compressor RLA and the other loads.
Is this a code compliance check?
No. It is a calculation aid built from the figures the Equipment Tracker app uses. Local electrical code and the authority having jurisdiction decide what is allowed, so check local code before you size or replace wiring or a breaker.
Does this page store anything or need an account?
No to both. The calculator runs in your browser and nothing is saved when you close the tab. If you want the equipment, its electrical details and service history kept on each unit, that is what Equipment Tracker is for.
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