312.1 Scope.

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Article 312 does NOT apply to equipment operating over 1000 volts unless specifically referenced elsewhere in the NEC.

Code Change Summary: A new sentence was added to address the scope of Article 312.

Article 312 is all about cabinets, cutout boxes and meter socket enclosures. Meter socket enclosures are self-explanatory but the other two have an actual definition in Article 100:

Cabinet. An enclosure that is designed for either surface mounting or flush mounting and is provided with a frame, mat, or trim in which a swinging door or doors are or can be hung.

Cutout Box. An enclosure designed for surface mounting that has swinging doors or covers secured directly to and telescoping with the walls of the enclosure.

Cabinets are the most common enclosure used for most panelboards. According to UL, a cabinet consists of two parts: a cabinet box and a mating cabinet front that contains a door.

Cutout boxes are provided with a door secured by hinges and one or more fasteners and are intended for surface mounting.

The UL White book states the following:

One of the following product identities appears on the product:

• Cutout Box (for the surface-mounted box provided with a door).
• Electric Cabinet Box (for the box only).
• Electric Cabinet Front (for the front trim or matt used on the flush- or surface-mounted cabinet box).

In the 2017 NEC^®, an additional sentence was added to the scope of Article 312 to make it clear that the article does NOT apply to equipment operating over 1000 volts, except as specifically referenced elsewhere in the Code. This change was important so that installers will be sure to follow the guidelines in Article 490 rather than 312 when installing equipment over 1000 volts.

Article 490 has specific rules that must be followed on the minimum clearances between an enclosure and the live parts inside the enclosure operating over 1000 volts.

Below is a preview of Article 312. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.