The Ultimate Guide to Choosing the Right Circuit Breaker Size for Your Mini Split

When it comes to ensuring the safe and efficient operation of your mini split system, selecting the appropriate circuit breaker size is crucial. This comprehensive guide will delve into the technical details and provide you with a step-by-step approach to determining the optimal circuit breaker size for your mini split.

Understanding the Minimum Circuit Ampacity (MCA)

The Minimum Circuit Ampacity (MCA) represents the smallest wire size that can handle the electrical load without overheating. For a typical mini split, the MCA is usually 20 amps, which corresponds to a 10 AWG (American Wire Gauge) wire. To calculate the MCA, you’ll need to refer to the manufacturer’s specifications or the data plate on the mini split unit.

Calculating the MCA

To calculate the MCA, follow these steps:

  1. Locate the full-load amperage (FLA) or the maximum operating current (MOC) on the mini split’s data plate or in the manufacturer’s specifications.
  2. Multiply the FLA or MOC by 125% to determine the MCA.
  3. Example: If the FLA is 16 amps, the MCA would be 16 amps x 1.25 = 20 amps.

Determining the Maximum Overcurrent Protection (MOP)

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The Maximum Overcurrent Protection (MOP) is the highest current that a circuit breaker or fuse can safely interrupt during a short circuit. For a mini split, the MOP is often 25 amps, which means you should use a two-pole 25-amp breaker.

Selecting the Appropriate Breaker Size

When choosing the circuit breaker size, consider the following:

  1. If the MCA is 20 amps, use a two-pole 25-amp breaker.
  2. If the MCA is higher than 20 amps, you may need to use a larger breaker size, such as a 30-amp or 40-amp breaker.
  3. Consult the manufacturer’s recommendations or the National Electrical Code (NEC) for specific guidelines on the appropriate breaker size for your mini split model.

Sizing the Conductor (Wire)

The NEC requires that conductors be sized to handle the MCA. For a 20-amp MCA, you should use 10 AWG wire. However, if you’re using a 25-amp breaker, you can still use 10 AWG wire, as it can safely handle up to 30 amps.

Choosing the Appropriate Wire Size

  1. Determine the MCA, as calculated earlier.
  2. Refer to the NEC table for the appropriate wire size based on the MCA.
  3. For a 20-amp MCA, use 10 AWG wire.
  4. For a 25-amp breaker, you can use 10 AWG wire.
  5. Ensure the wire size can handle the maximum current without overheating.

Fused vs. Non-Fused Disconnect

The type of disconnect you use for your mini split depends on the manufacturer’s recommendations. If the label on the unit specifically mentions a fuse, it’s recommended to use a fused disconnect. Otherwise, a non-fused disconnect is acceptable.

Selecting the Appropriate Disconnect

  1. Check the manufacturer’s instructions or the data plate on the mini split unit to determine if a fused or non-fused disconnect is required.
  2. Ensure the disconnect is rated for the same current as the circuit breaker (e.g., 25 amps).

Addressing Startup Surge Protection

During startup, mini splits can draw significantly more current than their running load. To account for this, you can use a time-delay fuse or a 25-amp breaker with a 20-amp time-delay fuse in the disconnect.

Implementing Surge Protection

  1. Determine if the mini split manufacturer recommends using a time-delay fuse or a breaker with a time-delay fuse.
  2. Install the appropriate time-delay fuse or breaker with a time-delay fuse in the disconnect to protect against startup surges.

By following these detailed guidelines, you can ensure that your mini split system is properly protected and operating at its best. Remember to always consult the manufacturer’s instructions and adhere to the National Electrical Code for the safest and most efficient installation.

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