Which piece of equipment is specifically covered under Article 300 when it's factory installed?

The piece of equipment that is specifically covered under Article 300 when factory installed is panelboards. Article 300 of the National Electrical Code (NEC) addresses general requirements for wiring methods and materials and includes provisions that specifically pertain to how electrical equipment, such as panelboards, should be installed, used, and maintained.

Panelboards are crucial for distributing electrical power throughout a building, and they often include circuit breakers or fuses that provide overcurrent protection for various branch circuits. When these units are factory installed, they must comply with the NEC requirements, including proper mounting, access, and grounding.

The distinction for panelboards under Article 300 lies in the detailed requirements that outline their structural integrity, accessibility, and methods for safe operation, thus ensuring that they are installed in a way that maintains the safety and reliability of the electrical system.