You're on the right track! Let's break down 440.22(B)(1) and what it's referring to in 440.22(A).

Understanding the Goal

The goal of this section is to determine the maximum allowed size of the breaker or fuse (the "branch-circuit short-circuit and ground-fault protective device") that will safely protect the air conditioning equipment. It's important to note that you don't have to size the breaker to the maximum allowed; you can use a smaller breaker if your calculations and the equipment requirements permit.

What 440.22(A) Tells Us

Section 440.22(A) gives the rules for sizing the overcurrent protection for a single motor-compressor. It's the starting point for determining the maximum breaker size in your multiple motor/load scenario. It outlines that the overcurrent protection should not exceed: 175% of the motor-compressor's rated-load current (RLA). This is the default maximum. Up to 225% of the motor-compressor's RLA, but only if the 175% rule isn't sufficient to allow the motor-compressor to start and run. The NEC directs you to make an engineering judgement call.

Answering Your Question

In 440.22(B)(1), when it refers to "the value specified in 440.22(A)", it means the calculated value based on the motor-compressor's rated-load current multiplied by 175% (or up to 225% if needed for starting).Here's how it works in practice


Largest Motor-Compressor

Identify the largest motor-compressor in the AC unit (the one with the highest RLA).2.

Calculate the Maximum Overcurrent Protection for the Largest Motor-Compressor (using 440.22(A))

Multiply the largest motor-compressor's RLA by 1.75 (175%). This is your initial maximum value. If, after installing an overcurrent protective device sized using this first calculation, the motor-compressor trips the overcurrent device when starting up or during normal operation, you can increase that percentage to 225%.3.

Other Motor-Compressors and Loads

For each of the other motor-compressors, determine either: The rated-load current (RLA) of each motor-compressor. OR the branch-circuit selection current (if the equipment is marked with this, and this current is greater than the RLA). This is less common but exists for some equipment. For other loads, determine the rated currents for each.4.

Sum It Up

Add the following together: The calculated maximum value from step 2 (the largest motor-compressor, RLA 1.75 or RLA 2.25). The sum of the rated-load currents or branch-circuit selection currents (whichever is greater) of all other motor-compressors. The ratings of all other loads.

The result is the maximum allowed breaker/fuse size (MOCP) for the entire branch circuit. You can use a breaker/fuse smaller than this value if the equipment manufacturer's specifications permit it and if your calculations show it's sufficient.

Important Considerations



Nameplate Data is King

If the AC unit's nameplate provides an MOCP value, always use that value. The manufacturer has already done these calculations and likely included factors you might not be aware of. The NEC allows and encourages this.

Minimum Circuit Ampacity (MCA)

Remember to also check the AC unit's Minimum Circuit Ampacity (MCA) to ensure the conductors you use are appropriately sized. The MCA is the minimum allowable current-carrying capacity for the branch circuit conductors.*

Safety First

When in doubt, consult with a qualified electrical engineer or inspector. Air conditioning systems can be complex, and proper overcurrent protection is critical for safety and equipment longevity.

In summary, 440.22(A) provides the rules to determine the starting point 'value' for the largest motor-compressor, and then 440.22(B)(1) tells you how to combine that with the other loads to arrive at the final maximum breaker/fuse size. Flag for review