Most articles in the National Electrical Code (NEC) cover specific topics such as branch circuits, overcurrent protection, grounding and bonding, boxes, rigid metal conduit, motors, healthcare facilities, swimming pools and emergency systems. See the Table of Contents for all of the specific topics covered in the NEC. The first three articles are somewhat different because they contain the groundwork for the rest of the Code.


Article 90, Introduction, covers the purpose, scope and other information necessary to be able to understand the NEC. Article 100, Definitions, contains definitions essential to the proper application of the Code. As a general rule, Article 100 defines only the terms that are used in two or more articles. For a term that is used in only one article, it is defined in that article.


Article 110, “Requirements for Electrical Installations,” covers a broad collection of topics, including examination, installation and use of electrical equipment; mechanical execution of work; temperature limitations; arc-flash hazard warnings; and spaces about electrical equipment.


Requirements for disconnecting means can be found in dozens of articles throughout the Code. Article 110 is the first article containing such requirements. (The term “disconnecting means” appears in Article 100, but it does not contain any requirements.) Before looking at the first disconnecting means requirement, it is essential to understand the term itself. As Article 100 defines, disconnecting means is a device, group of devices or other means whereby circuit conductors can be disconnected from their source of supply.


While there are many types of disconnecting means, one is a safety switch, commonly referred to as a “disconnect” or “disconnect switch.” A disconnect switch can be fused or nonfused. Other items that are disconnecting means include, but are not limited to, an individual circuit breaker, circuit breakers in a panelboard, a combination motor starter, and a manual motor starter (see Figure 1).


Article 100 also defines the term “panelboard” as a single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition or other support; and accessible only from the front. A panelboard can be thought of as the guts that are inside an electrical panel. “Panelboard” usually means the complete unit, which includes the guts and the cabinet or cutout box.


Article 100 defines a cabinet as an enclosure designed for either surface- or flush-mounting and is provided with a frame, mat or trim in which a swinging door or doors are or can be hung (see Figure 2).


A cutout box is similar, but this enclosure is designed for surface mounting only. A cutout box also has swinging doors or covers secured directly to and telescoping with the walls of the box. The enclosure for a safety switch or disconnect switch is one example of a cutout box. Disconnecting means also is defined in Article 551, but the definition in 551.2 applies to recreational vehicles and RV parks only. In Article 551, disconnecting means is the necessary equipment usually consisting of a circuit breaker or switch and fuses, and their accessories, located near the supply conductors point of entrance in a recreational vehicle and intended to constitute the means of cutoff for the supply to that RV.


As previously mentioned, requirements for disconnecting means are throughout the Code; Article 110 contains several of these requirements. The first, located in 110.22(A), states each disconnecting means shall be legibly marked to indicate its purpose. Because of the definition of a disconnecting means, this provision applies to many different types of equipment, such as fused and nonfused disconnect switches, circuit breakers in panelboards and switchgear (see Figure 3).


The provision in 110.22(A) also states that, if the purpose of the disconnecting means is obvious because of where it is located, it is not required to mark the purpose of the disconnecting means. For example, a safety switch or disconnect is supplying power to a rooftop air conditioning unit and is mounted on the unit. Since it is obvious the disconnect is supplying power to the air conditioning unit, marking this disconnecting means to indicate its purpose is not required (see Figure 4).


The last sentence in 110.22(A) requires the marking to be of sufficient durability to withstand the environment. For example, two disconnect switches are located outside a building. The disconnect on the left supplies power to panelboard LJM, located in Building 2. The right disconnect supplies power to panelboard CRM, located in Building 3. Since these disconnects are situated outside, writing on the front of the disconnect with a permanent marker would be a violation of the last sentence in 110.22(A). For this example, engraved, UV-coated plastic nameplates will be installed on the front of each disconnect to indicate the purpose (see Figure 5).


Identification requirements for switchboards, switchgear and panelboards are also in Article 408. In accordance with 408.4(A), every circuit and circuit modification shall be legibly identified as to its clear, evident and specific purpose or use. The identification shall include an approved degree of detail that allows each circuit to be distinguished from all others. Marking a circuit in a panelboard “Lights and Receptacles” would not be enough detail to differentiate the lights and receptacles supplied by this circuit breaker from those supplied by other circuit breakers.


This section also requires circuit breakers that are installed in the panelboard but not supplying conductors to be described accordingly. An easy way to describe an unused circuit breaker is to mark it “Spare.” For a panelboard, the identification can be a circuit directory located on the face or inside of the panel door. For a switchboard or switchgear, the identification can be a circuit directory located at each switch or circuit breaker (see Figure 3).


The last sentence in 408.4(A) states that no circuit shall be described in a manner that depends on transient conditions of occupancy. If the description of the circuit is based on a temporary condition of occupancy, the circuit description would be a violation of 408.4(A). A circuit breaker will supply power to a ceiling-suspended (paddle) fan with a luminaire (lighting fixture) and six receptacles in one of the bedrooms in a new dwelling.


This particular bedroom will be Billy’s bedroom. Labeling this circuit “Billy’s Bedroom” would be a violation of 408.4(A) because the description is based on a transient condition of occupancy. Labeling this circuit “Fan/Light and Receptacles in the Southwest Corner Bedroom” is permitted because the location of this bedroom will never change. If the blueprints have this bedroom labeled as Bedroom 2, then labeling this circuit “Fan/Light and Receptacles in Bedroom 2” would also be permitted.


Next month’s column continues the discussion of electrical installation requirements.