🔌 Recommended Breaker Size
Breaker Selection Breakdown
Full Calculation Table
| Value | Basis | Result |
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How to Use the Breaker Size Calculator
If the nameplate lists MOCP directly, use that. If you only have FLA, the calculator applies the standard 125% to 175% sizing range used for motor branch circuits.
Compressors and motors need HACR-rated breakers and tolerate brief overcurrent for starting. Resistive heat strips don't have inrush current and use simpler sizing rules.
MCA sets the floor. The calculator will never recommend a breaker below this value, even if a smaller standard size would otherwise fit.
The calculator rounds to the next standard breaker size per CEC Table 13 and flags whether a HACR-type breaker is required.
Choosing the Right Breaker Size for HVAC Equipment
Circuit breaker sizing for HVAC equipment isn't as simple as matching the breaker to the running amperage. Motors and compressors draw a large inrush current for a fraction of a second at startup, sometimes 4 to 6 times their running amps, and a breaker sized too tight will nuisance-trip every time the unit starts. That's why manufacturers list a Maximum Overcurrent Protection (MOCP) value on the nameplate that's already built with this headroom in mind.
Why MOCP Sets the Ceiling, Not the Target
MOCP is the largest breaker the equipment is rated to use safely, not a recommendation to always use the biggest size available. Going larger than MOCP removes the short-circuit protection the equipment was tested with. Going smaller is allowed and often necessary when the actual standard breaker size that matches MOCP exactly doesn't exist, in which case you round up to the next standard size below MOCP, never above it.
Standard Breaker Sizes in Canada
CEC Table 13 lists the standard ampere ratings for fuses and circuit breakers: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, and larger. When a calculated value falls between two standard sizes, you round up to the next size, as long as that size doesn't exceed the equipment's MOCP. This calculator handles that rounding automatically.
HACR-Type Breakers
HACR stands for Heating, Air Conditioning, and Refrigeration. These breakers are tested and listed specifically to handle the brief inrush current and time-delay tripping characteristics that compressor and motor loads need. Most HVAC equipment installation instructions require a HACR-rated breaker, and CEC Rule 2-100 makes following the manufacturer's instructions mandatory. A standard breaker without the HACR rating can nuisance-trip on startup even when it's correctly sized for the running load.
Working from Full Load Amps Instead of MOCP
If the nameplate only lists FLA without a separate MOCP value, the standard approach for a single motor is to size the breaker at 125% to 175% of FLA depending on motor type, then round to the next standard size. This calculator applies a reasonable default for this range, but always defer to the exact MOCP or MCA value when one is printed on the equipment, since it reflects the manufacturer's actual testing rather than a general formula. The MCA / MOCP calculator can work out both values from raw nameplate data.
Next Steps
Once you've confirmed the breaker size, check the wire size calculator to make sure the conductor is rated for at least the MCA, and the voltage drop calculator if the circuit run is long. For equipment with a known short-circuit hazard, the short circuit calculator helps confirm the breaker's interrupting rating is adequate.
Frequently Asked Questions
For HVAC equipment with a listed MOCP, you can round up to the next standard breaker size if the exact MOCP value doesn't match one, but you can never round up past the MOCP value itself or round down below the calculated minimum circuit ampacity. Standard sizes follow CEC Table 13 and include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250 amps, and larger.
HACR stands for Heating, Air Conditioning, and Refrigeration. A HACR-type breaker is tested and listed for use with motor loads like compressors and condenser fans that draw a brief inrush current well above their running amperage at startup. Most residential air conditioners, heat pumps, and furnaces with HVAC blower motors require a HACR-rated breaker per the equipment manufacturer's installation instructions, which CEC Rule 2-100 requires you to follow.
MCA, or Minimum Circuit Ampacity, is the smallest wire size the circuit is allowed to use. MOCP, or Maximum Overcurrent Protection, is the largest breaker or fuse allowed on that circuit. The breaker you choose must be at or above the MCA-rated wire's ampacity and at or below the MOCP value, which is why both numbers matter for a correct installation. See the MCA / MOCP calculator for a full breakdown of both values from nameplate data.
Nuisance tripping on startup usually means the breaker isn't HACR-rated, is sized too close to the running amperage without enough headroom for inrush current, or the compressor itself is drawing higher than normal starting current due to a mechanical or electrical fault. Confirm the breaker matches the equipment's MOCP and is HACR-listed before assuming the unit itself has a problem.
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