EC&M Tech Talk — Sizing Conductors & Protection for Motors, HVAC Equipment, and Generators

Sizing conductors and protection for rotating electrical equipment is commonly required in the field and on exams. The rules are separate for different types of equipment and can become quite involved. In this EC&M Tech Talk Randy Barnett first overviews the 2026 NEC changes to three articles that address rotating equipment installation, then provides practical examples:

•    Article 430 Motors
•    Article 440 Air-Conditioning and Refrigerating Equipment
•    Article 445 Generators

Using onscreen single line diagrams, Randy reviews the requirements for sizing the short-circuit and ground-fault protection, the branch-circuit conductors and the overload protection for a 25 horsepower three-phase motor. This is also the same example from Informative Annex D8, which makes this part of the Tech Talk an excellent learning tool that can be applied in the field or used in exams.  

Sizing conductors and overcurrent protection for a typical residential or commercial HVAC requires an understanding Article 440. These units typically have two motors – but they are not treated the same as motors in Article 430. Understanding the code requirements of Article 440 is the key!

Conductors from generator terminals to the first fuse or circuit breaker are not protected, other than by the design of the generator itself. The rules are basic and explained with the onscreen diagram. Two new additions to this article refer code users to specific articles for sizing the neutral conductor supplied from a generator and the grounding electrode conductor for the generator.

Sizing conductors for rotating equipment can be tricky if you don’t understand the complexity of the rules. This Tech Talk will put those rules into plain and simple language using practical applications.