NEC: Air Conditioning and Refrigerating Equipment — Part 3

Article 440, Part 3 provides the requirements for the branch-circuit short-circuit and ground-fault protection used in HVAC and refrigeration equipment. That is, it provides the requirements for overcurrent protective devices (OCDPs) for hermetic motor circuits.

These requirements are not standalone, however. They supplement or amend the overcurrent protection requirements that apply to non-hermetic motor circuits [440.21]. This fact can make compliance a bit tricky. So here’s a pro tip: Proceed as if you are installing a non-hermetic motor, then look in Art. 440, Part 3 to see if there is an applicable set of requirements.

For example, suppose you are sizing the OCPD for an individual motor-compressor. You proceed as if you are sizing the OCPD for an individual non-hermetic motor. You start with the requirements in Art. 430. But that’s a big Article — how can you quickly locate the requirements? Go to Figure 430.1. You will see on the fourth tier of the drawing, “Motor branch-circuit short-circuit and ground-fault protection.” Part 4 is right across from it. Bingo.

When you go to 430 Part IV, you’ll see “430.52. Rating or Setting for Individual Motor Circuit.” This corresponds with “440.22. Single Motor-Compressor.” 430.52 underwent heavy revision with the 2023 cycle, and now you’re going to effectively revise it again by noting and applying the differences in 440.22. Before you read through the 430.52 requirements, understand what the 440.22 requirements are. And if you’ll notice, they are much simpler. No need to mess with Table 430.52(C)(1) and the rating rules that follow. All you have to do is use an OCPD that can carry the starting current and that does not exceed the greater of two values:

1. 175% of the motor-compressor rated-load current.
2. 175% of the branch-circuit selection current.

But you may need to use one of the two Exceptions if you can't start the motor by following the 175% rule.

Now, there is an even bigger shortcut that may exist for your particular installation. In many cases, the manufacturer has designed a “ready-to-go” package. If you install a Brand X Model 123XYZ HVAC unit, it is likely the manufacturer has already determined what disconnect and OCPD to use. The manufacturer does this for multiple reasons, such as reducing support tickets and warranty claims. If you’re putting together a bill of materials for installing such a system, check the installation instructions to see if this work has already been done for you.