3.2 Key Article 100 Definitions for the Exam

3.2 Key Article 100 Definitions for the Exam

Article 100 contains definitions essential to the proper application of the National Electrical Code. In the Colorado Journeyman examination, terminology questions are among the easiest points to secure if you know the exact statutory wording—and the easiest to lose if you rely on jobsite slang. In modern editions of the NEC, all definitions from throughout the Code are consolidated into Article 100, organized alphabetically.

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Accessible vs. Readily Accessible

Perhaps no distinction is tested more frequently on Colorado Journeyman exams than the difference between Accessible (in its two applications) and Readily Accessible.

┌────────────────────────────────────────────────────────────────────────────────────────┐
│                          ACCESSIBILITY COMPARISON CHART                                │
├──────────────────────────┬─────────────────────────────┬───────────────────────────────┤
│ Term                     │ Statutory Definition        │ Jobsite Examples & Conditions │
├──────────────────────────┼─────────────────────────────┼───────────────────────────────┤
│ Accessible               │ Capable of being removed or │ • Junction box above lay-in   │
│ (as applied to wiring    │ exposed without damaging    │   drop ceiling                │
│ methods)                 │ the building structure or   │ • Wiring inside a removable   │
│                          │ finish. Not permanently     │   access panel                │
│                          │ closed in by structure.     │ • (Behind sheetrock = NOT ok) │
├──────────────────────────┼─────────────────────────────┼───────────────────────────────┤
│ Accessible               │ Admitting close approach;   │ • Disconnect in locked room   │
│ (as applied to           │ not guarded by locked doors,│   where keys are held by      │
│ equipment)               │ elevation, or other         │   authorized personnel        │
│                          │ effective means.            │ • Equipment on open platform  │
├──────────────────────────┼─────────────────────────────┼───────────────────────────────┤
│ Readily Accessible       │ Capable of being reached    │ • Service disconnect switch   │
│                          │ quickly for operation,      │ • Overcurrent devices         │
│                          │ renewal, or inspections     │ • Emergency shutoff switches  │
│                          │ WITHOUT requiring climbing, │ • GFCI reset buttons          │
│                          │ portable ladders, chairs,   │ • (Requiring a ladder =       │
│                          │ or removing obstacles.      │   NOT READILY ACCESSIBLE)     │
└──────────────────────────┴─────────────────────────────┴───────────────────────────────┘

Key Practical Rules Governed by Accessibility:

• Overcurrent Devices (NEC 240.24(A)): Circuit breakers and fuses must be readily accessible. An overcurrent device cannot be mounted higher than 6 feet 7 inches (2.0 m) above the floor or working platform to the center of the grip of the operating handle in its highest position.
• Service Disconnecting Means (NEC 230.70(A)(1)): Must be installed in a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors.
• Junction Boxes (NEC 314.29): Must be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or, in a building completed prior to the installation of the box, without removing the finish.

Exam Trap: If an electrical panel or disconnect is mounted on a rooftop that requires climbing a portable extension ladder through a roof hatch, it is accessible, but it is NOT readily accessible. If a permanent stairway or permanent exterior ship's ladder leads to the roof, equipment on that roof level can be readily accessible once on the roof, but it is not readily accessible from grade level.

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Continuous Load (The 125% Multiplier)

Article 100 defines a Continuous Load as:

"A load where the maximum current is expected to continue for 3 hours or more."

This simple definition is the mechanical trigger for calculations across Articles 210, 215, 220, and 230:

• Branch Circuit Rating (NEC 210.19(A)(1) & 210.20(A)): Conductor ampacity and the overcurrent protective device rating must be not less than the noncontinuous load plus 125% of the continuous load:

$\text{Minimum OCPD / Conductor Rating} = \text{Noncontinuous Load} + (1.25 \times \text{Continuous Load})$

Common Continuous Loads on the Exam:

• Commercial lighting systems (store, office, warehouse lighting operating throughout business hours).
• Fixed electric space heating (NEC 424.3(B)).
• Electric vehicle branch circuits (NEC 625.41).
• Commercial water heaters having a capacity of 120 gallons or less (NEC 422.13).

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Ampacity

Article 100 defines Ampacity as:

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

Three foundational elements form this definition:

1. Continuously: It represents continuous thermal steady-state carrying capacity.
2. Conditions of Use: Actual ampacity is modified by ambient temperature (Table 310.16 correction factors) and conductor bundling (Table 310.15(C)(1) adjustment factors).
3. Temperature Rating: The limits of the conductor insulation (60°C, 75°C, or 90°C) and the connected termination lugs (NEC 110.14(C)).

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Fault Conditions: Ground Fault, Short Circuit, Overload & Overcurrent

The NEC makes precise scientific distinctions among abnormal electrical conditions. You will see these on the Colorado PSI exam:

                         ┌─────────────────────────────────────────┐
                         │          OVERCURRENT (UMBRELLA)         │
                         │ Any current in excess of rated current  │
                         │ or ampacity (Equipment rating / wire)   │
                         └────────────────────┬────────────────────┘
                                              │
         ┌────────────────────────────────────┼────────────────────────────────────┐
         ▼                                    ▼                                    ▼
┌──────────────────────────────┐ ┌──────────────────────────────┐ ┌──────────────────────────────┐
│           OVERLOAD           │ │        SHORT CIRCUIT         │ │         GROUND FAULT         │
│ • Excess current in normal   │ │ • Fault connection between   │ │ • Fault connection between   │
│   closed circuit paths       │ │   ungrounded conductors of   │ │   an ungrounded conductor    │
│ • Caused by mechanical       │ │   different potential        │ │   and normally non-current-  │
│   equipment loading, motor   │ │ • Line-to-line or            │ │   carrying metal enclosures, │
│   stalls, or plugged devices │ │   line-to-neutral            │ │   raceways, EGC, or earth    │
│ • NOT a short or fault!      │ │ • Extremely high current     │ │ • Cleared by effective       │
│ • Moderate thermal buildup   │ │ • Fast magnetic trip         │ │   fault current path (MBJ)   │
└──────────────────────────────┘ └──────────────────────────────┘ └──────────────────────────────┘

• Overcurrent: Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.
• Overload: Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or a ground fault, is not an overload.
• Short Circuit: An abnormal connection of relatively low impedance, whether made intentionally or unintentionally, between two points of different potential (e.g., phase-to-phase or phase-to-neutral).
• Ground Fault: An unintentional, electrically conductive connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

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Bonding Jumpers: Main, Equipment & System

Bonding is the practice of connecting metallic parts together to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any fault current likely to be imposed.

• Main Bonding Jumper (MBJ): The connection between the grounded circuit conductor (neutral) and the equipment grounding conductor at the service (NEC 250.24(B), 250.28). This is the single bond that enables ground-fault current to return to the utility transformer source and trip the service breaker.
• Equipment Bonding Jumper (EBJ): The connection between two or more portions of the equipment grounding conductor (e.g., bonding a metal conduit to an enclosure across a concentric knockout).
• System Bonding Jumper (SBJ): The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system (such as a local dry-type step-down transformer).

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Circuit Conductors: Service vs. Feeder vs. Branch Circuit

Utility Point of Delivery (Service Point)
       │
       ▼ [Service Conductors]
Service Disconnect / Service Equipment (Main OCPD)
       │
       ▼ [Feeder Conductors]
Distribution Subpanel (Panelboard OCPD)
       │
       ▼ [Branch-Circuit Conductors]
Outlet / Final Utilization Equipment (Receptacle, Motor, Luminaire)

• 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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Other Heavily Tested Article 100 Definitions

• Separately Derived System: An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections. Examples include generators with switched neutrals, solar microinverters, and standard delta-to-wye transformers.
• Identified (as applied to equipment): Recognizable as suitable for the specific purpose, function, use, environment, application, etc., where described in a particular Code requirement.
• Listed: Equipment, materials, or services included in a list published by an organization that is acceptable to the AHJ (such as UL, ETL, CSA) and concerned with product evaluation.
• Labeled: Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization acceptable to the AHJ and concerned with product evaluation.