2.1 NEC Article 100 Definitions & Article 110 General Installation Requirements

2.1 NEC Article 100 Definitions & Article 110 General Installation Requirements

Navigating the National Electrical Code (NEC / NFPA 70) and passing the Wisconsin Journeyman Electrician licensing examination requires an uncompromising command of code definitions and fundamental installation rules. NEC Article 100 establishes the legal vocabulary of the electrical industry, while Article 110 dictates how equipment must be selected, mechanically secured, electrically connected, and physically safeguarded.

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1. Crucial Article 100 Definitions Frequently Tested

Licensing examiners regularly test Article 100 terms because misunderstandings directly cause field code violations. Below are the most critical definitions and their precise code distinctions.

Accessible vs. Readily Accessible vs. Accessible (as Applied to Equipment)

The code defines three distinct tiers of accessibility:

Exam Tip: If reaching a component requires grabbing a six-foot stepladder from your service truck, that component is Accessible, but it is emphatically NOT Readily Accessible.

Bonded (Bonding) vs. Grounded (Grounding)

• Bonded (Bonding): Connected to establish electrical continuity and conductivity between metal parts required to be electrically connected. Bonding ensures a low-impedance path capable of safely conducting prospective fault currents to facilitate overcurrent device operation.
• Grounded (Grounding): Connected (intentionally or accidentally) to ground (the earth) or to a conductive body that extends the ground connection.
• Grounded Conductor: A system or circuit conductor that is intentionally grounded (universally identified as the neutral conductor in typical AC distribution systems).
• Equipment Grounding Conductor (EGC): The conductive path(s) installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor, the grounding electrode conductor, or both.

Continuous Load

NEC Article 100 defines a Continuous Load as:

$\text{Continuous Load: Maximum current expected to continue for } 3 \text{ hours or more.}$

Under NEC 210.19(A)(1) and 215.2(A)(1), conductors and overcurrent protective devices supplying continuous loads must be sized at 125% of the continuous load plus 100% of any non-continuous load.

Ampacity

The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating (measured in amperes).

Device vs. Equipment vs. Utilization Equipment

• Device: A unit of an electrical system, other than a conductor, that carries or controls electric energy as its principal function (e.g., switches, receptacles, circuit breakers, fuses). Devices do not consume electrical energy.
• Equipment: A general term including materials, fittings, devices, appliances, luminaires, apparatus, machinery, and parts used in connection with an electrical installation.
• Utilization Equipment: Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes (e.g., motors, electric water heaters, luminaires, commercial ovens). Utilization equipment consumes energy.

Feeder vs. Branch Circuit vs. Service Conductors

• Service Conductors: The conductors from the service point to the service disconnecting means.
• Feeder: All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.
• Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

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2. Article 110 General Installation Requirements

Article 110 sets enforceable baselines for safety, workmanship, and environmental endurance.

Mechanical Execution of Work (NEC 110.12)

Electrical equipment must be installed in a neat and workmanlike manner. While this sounds subjective, specific sub-rules provide legal teeth:

1. Unused Openings (NEC 110.12(A)): Unused cable or raceway openings in boxes, raceways, auxiliary gutters, cabinets, and cutout boxes must be effectively closed to afford protection substantially equivalent to the wall of the enclosure. If knockout seals are used, they must be listed and properly seated.
2. Integrity of Internal Parts (NEC 110.12(B)): Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and surfaces, must not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues.

Deteriorating Agents & Environmental Integrity (NEC 110.11)

Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other deteriorating agents; or where exposed to excessive temperatures.

Equipment intended for outdoor use must be selected based on its enclosure environmental rating (NEMA / NEC Table 110.28). For example, NEMA 3R protects against falling rain, sleet, and external ice formation, while NEMA 4X provides washdown protection and corrosion resistance.

Electrical Connections & Terminal Torque Requirements (NEC 110.14(D))

Electrical failures are overwhelmingly thermal failures caused by improper terminations. NEC 110.14(D) requires that:

1. Where a tightening torque is indicated as a numeric value on equipment or in installation instructions provided by the manufacturer, a calibrated torque tool (torque screwdriver or torque wrench) must be used.
2. Installers cannot rely on "feel" or muscle memory. Tightening terminal lugs without a calibrated tool is an explicit violation of the NEC.
3. Terminations must use compatible materials (e.g., connectors marked AL7CU for aluminum or copper conductors rated 75°C, or AL9CU rated 90°C).

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3. Spaces About Electrical Equipment (NEC 110.26)

Sufficient access and working space must be provided and maintained around all electrical equipment to permit ready and safe operation and maintenance. These rules apply to equipment operating at 1000V nominal or less that is likely to require examination, adjustment, servicing, or maintenance while energized.

Working Space Depth (NEC 110.26(A)(1))

The depth of the working space in the direction of live parts is governed by NEC Table 110.26(A)(1), categorized into three distinct environmental conditions:

• Condition 1: Exposed live parts on one side of the working space and no live or grounded parts on the other side, or exposed live parts on both sides effectively guarded by suitable wood or other insulating materials.
• Condition 2: Exposed live parts on one side of the working space and grounded parts on the other side. Concrete, brick, tile, and masonry walls are recognized by the code as grounded surfaces.
• Condition 3: Exposed live parts on both sides of the working space (not guarded) with the operator working between them.

Exam Warning: On exam questions involving a 120/208V 3-phase, 4-wire system, the voltage to ground is 120V (0–150V band), requiring a 3 ft depth regardless of condition. However, for a 277/480V 3-phase, 4-wire system, the voltage to ground is 277V (151–600V band). If installed across from a concrete basement wall (Condition 2), the required depth is 3 feet 6 inches!

Working Space Width (NEC 110.26(A)(2))

1. The width of the working space in front of the electrical equipment must be a minimum of 30 inches (762 mm) or the width of the equipment, whichever is greater.
2. In all cases, the work space must permit at least a 90-degree opening of equipment doors or hinged panels.
3. The equipment is not required to be centered within the 30-inch workspace; the workspace can extend to the left, right, or center, provided the 30-inch clear zone is maintained.

Working Space Height / Headroom (NEC 110.26(A)(3))

The minimum headroom of working spaces about service equipment, switchboards, panelboards, or motor control centers must be:

$\text{Minimum Headroom} = \max(6\text{ ft } 6\text{ in. } [2.0\text{ m}], \text{ Height of Equipment})$

Exception: In existing dwelling units, service equipment or panelboards that do not exceed 200 amperes are permitted in spaces where the headroom is less than 6 ft 6 in.

Dedicated Equipment Space (NEC 110.26(E))

Switchboards, switchgear, panelboards, and motor control centers must have dedicated equipment space:

1. Indoor Installations (NEC 110.26(E)(1)):
   • Dedicated Electrical Space: The footprint equal to the width and depth of the equipment extending from the floor to a height of 6 feet (1.8 m) above the equipment or to the structural ceiling, whichever is lower. No piping, ducts, leak protection apparatus, or foreign systems can enter or pass through this zone.
   • Foreign Systems: Permitted above the 6-foot dedicated zone only if protection (such as drip pans) is installed to prevent condensation, leaks, or breaks from damaging the electrical equipment.
2. Outdoor Installations (NEC 110.26(E)(2)): Outdoor electrical equipment must be protected from accidental contact, vehicle strikes, and spillage or leakage from foreign systems.

Large Equipment Entrances & Panic Hardware (NEC 110.26(C)(2) & (C)(3))

When electrical equipment is large, arc-flash hazards create catastrophic egress risks. The NEC enforces strict entrance and door hardware rules:

1. Threshold for Large Equipment: Equipment rated 1200 amperes or more AND over 6 feet (1.8 m) wide that contains overcurrent devices, switching devices, or control devices.
2. Dual Entrances Required (NEC 110.26(C)(2)): There must be at least one entrance/egress door of not less than 24 inches wide and 6.5 feet high at each end of the working space.
   • Exception 1 (Unobstructed Egress): A single entrance/exit door is permitted where the location permits a continuous and unobstructed way of egress travel.
   • Exception 2 (Double Work Space Depth): A single entrance/exit door is permitted where the depth of the working space is twice the depth required by Table 110.26(A)(1).
3. Panic Hardware Mandate (NEC 110.26(C)(3)): Where personnel doors are intended for entrance and egress from the working space and are located within 25 feet (7.6 m) from the nearest edge of the working space, the doors must:
   • Open in the direction of egress (outward opening).
   • Be equipped with listed panic hardware or fire exit hardware that unlatches under simple pressure (e.g., push bars, touch pads).