How do I Calculate MCA?


The minimum circuit ampacity (MCA) calculation for air conditioners and heat pumps establishes the minimum size of the branch circuit conductors--control switches and wiring--you need to supply your A/C or heater unit. The MCA is usually published on the equipment's nameplate, but you can calculate it yourself after locating a few figures on your product.

Things You'll Need

  • Air conditioner data tag/nameplate
  • Heat pump data tag/nameplate
  • Calculator
  • Find your equipment's motor rated current (MRC) on the unit's data tag/nameplate or in the product catalog. Some manufacturers also call it the unit's full load amps (FLA). It is usually determined using high-current tests by the manufacturer.

  • Find your unit's heater current, which is also labeled either on the data tag/nameplate or the product catalog.

  • Use the data you collected to fill in the following equation and determine the MCA:

    MCA = 1.25 x [motor rated current + heater current]

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