Add every motor and resistive load on this circuit. Mark the largest motor (usually the compressor) so the calculator applies the correct 125%/225% factors to it.
📋 MCA to MOCP Range
Calculation Breakdown
Full Calculation Table
| Load | FLA | Factor | Contribution |
|---|
How to Use the MCA / MOCP Calculator
Add the compressor, condenser fan motor, indoor blower motor, and any electric heat strip sharing the same circuit, each with its nameplate FLA.
This is almost always the compressor on HVAC equipment. The calculator applies the higher 125% (MCA) and 225% (MOCP) factors to this load only.
The calculator returns MCA for wire sizing and MOCP for breaker sizing, rounding MOCP down to the next standard breaker size.
Understanding MCA and MOCP on HVAC Nameplates
Almost every piece of packaged HVAC equipment, from a residential heat pump to a rooftop unit, lists MCA and MOCP directly on the nameplate. These two numbers tell the installer everything needed to size the branch circuit correctly without having to add up every individual motor and heater on the unit by hand. This calculator works backward from the individual nameplate FLA values when MCA and MOCP aren't already printed, or lets you verify a printed value against the underlying calculation.
How MCA Is Calculated
MCA takes 125% of the largest motor's full load amps, typically the compressor, then adds 100% of the full load amps for every other motor and resistive load sharing the same circuit, such as the condenser fan motor and any electric heat strip. The 25% margin on the largest motor accounts for the higher continuous duty cycle that motor experiences compared to a load that only runs intermittently. The resulting MCA value is the minimum ampacity the circuit conductors must be rated to carry.
How MOCP Is Calculated
MOCP uses a larger multiplier on the same largest motor, typically 225% rather than 125%, again adding 100% of every other load on the circuit. This larger multiplier gives the breaker or fuse enough headroom to ride through the motor's brief starting inrush current without nuisance tripping. Because standard breaker sizes don't always land exactly on the calculated value, MOCP is rounded down to the next standard size below the calculated number, never rounded up past it.
Why MOCP Is Always Larger Than MCA
MCA sets the floor for wire size, while MOCP sets the ceiling for breaker size, and the gap between them exists specifically to handle motor starting current that's much higher than running current but only lasts a fraction of a second. A wire sized exactly to MCA paired with a breaker sized at MOCP is a normal, code-compliant combination, even though the breaker is rated well above the wire's steady-state ampacity, because the breaker's job is to protect against a sustained fault, not to trip on every brief starting surge.
When the Nameplate Already Lists MCA and MOCP
If the equipment nameplate already prints MCA and MOCP directly, use those values rather than recalculating from individual component FLA, since the manufacturer's listed values reflect actual testing of that specific unit. This calculator is most useful when you only have the individual component ratings, such as during a custom equipment build or when verifying an older nameplate against current standards.
Next Steps
Once you have MCA, use the wire size calculator to pick the correct conductor gauge. Once you have MOCP, the breaker size calculator confirms the right standard breaker size and whether it needs to be HACR-rated.
Frequently Asked Questions
MCA is calculated by taking 125% of the largest motor's full load amps, such as the compressor, then adding 100% of the full load amps for every other motor and resistive load on the same circuit, such as the condenser fan motor and any electric heat strip. The result is the minimum ampacity the circuit conductors must be rated for.
MOCP is the maximum breaker or fuse size allowed on the circuit, calculated using a higher percentage than MCA, typically 225% of the largest motor's full load amps plus 100% of all other loads, then rounded down to the nearest standard breaker size if the result doesn't land exactly on one. MOCP is always equal to or larger than MCA, giving headroom for motor starting current without exceeding what the equipment is rated to handle safely.
Always use the nameplate value when one is printed on the equipment. Manufacturers calculate MCA and MOCP based on the actual tested performance of that specific unit, which can include small adjustments this general calculation doesn't account for. This tool is most useful for verifying older nameplates, working with individual component data when no combined nameplate value exists, or sanity-checking a printed value.
The largest motor is whichever single motor has the highest full load amps, not necessarily the one with the highest horsepower if voltages or motor types differ. On equipment with multiple compressors or motors of similar size, compare their actual FLA values directly and apply the 125%/225% factors to the highest one.
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