2.1 Key NEC Definitions (Article 100)
Key Takeaways
- Article 100 defines the terms the NEC uses as shorthand throughout the entire Code; the TX Journeyman exam tests these definitions directly and indirectly in nearly every question
- A branch circuit runs from the final overcurrent device to the outlet(s); a feeder runs from the service equipment (or separately derived source) to that final branch-circuit overcurrent device
- The grounded conductor is a current-carrying conductor intentionally grounded; the equipment grounding conductor (EGC) connects non-current-carrying metal parts to ground and is not a normal current carrier
- A continuous load is one where the maximum current is expected to last 3 hours or more, triggering the 125% sizing rule in 210.19(A)(1) and 210.20(A)
- Wet, damp, and dry location classifications in Article 100 determine which wiring methods and equipment are permitted, and they drive conduit, cable, and box selection throughout Chapters 3 and 4
Why Article 100 Matters for the TX Journeyman Exam
The Texas Journeyman Electrician exam's NEC Knowledge part gives you 59 questions in 130 minutes, open-book with the 2023 NEC. Nearly every question references Code language that hinges on Article 100 definitions. If you confuse a feeder with a branch circuit, you will look in the wrong article and waste precious minutes. If you confuse a grounded conductor with an equipment grounding conductor, you will select the wrong table and the wrong answer. Article 100 is the single highest-leverage page in the book for exam speed and accuracy.
The exam does not merely ask you to recite definitions. It embeds them in scenarios: "A conductor runs from the service disconnect to a panelboard containing branch-circuit breakers. What is this conductor?" Knowing the definition of feeder (Article 100) immediately tells you the answer and sends you to Article 215 (Feeders) for sizing, not Article 210 (Branch Circuits).
The Definitions You Must Know Cold
The table below covers the Article 100 definitions that appear most frequently on the exam. These are paraphrased for study; on the exam, the exact NEC wording governs.
| Term | NEC 2023 Definition (paraphrased) | Why It Matters on the Exam |
|---|---|---|
| Branch Circuit | The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). | Sends you to Article 210 for ratings, conductors, GFCI/AFCI, and receptacle rules. |
| Feeder | All circuit conductors between the service equipment, a separately derived source, or other power supply source and the final branch-circuit overcurrent device(s). | Sends you to Article 215 for feeder conductor sizing and overcurrent protection. |
| Service | The conductors and equipment for delivering electric energy from the serving utility to the premises wiring system. | Sends you to Article 230 for service conductors, disconnects, and grounding. |
| Service Equipment | The necessary equipment—usually circuit breaker(s) or switch(es) and fuse(s) and accessories—at the load end of service conductors, intended to be the main control and cutoff of the supply. | Determines the grounding point, the service disconnect requirements (230.71), and where the service overcurrent protection lives (230.91). |
| Separately Derived System | An electrical source, other than a service, having no direct electrical connection to circuit conductors of any other source other than connections through grounding and bonding. | Transformers, generators (with transfer switch), and PV systems. Sends you to 250.30 for grounding and bonding of the derived system. |
| Grounded Conductor | A system or circuit conductor that is intentionally grounded. | This is the neutral in most systems. It carries current under normal conditions and must be identified per 200.6. |
| Equipment Grounding Conductor (EGC) | The conductive path that connects normally non-current-carrying metal parts of equipment to the system grounded conductor or grounding electrode conductor. | Not a current carrier under normal conditions. Sized by Table 250.122. Sends you to Article 250 Part VI and VII. |
| Grounding Electrode Conductor (GEC) | The conductor used to connect the system grounded conductor or the equipment to the grounding electrode(s). | Connects the service (or SDS) to ground rods, water pipe, building steel. Sized by 250.66 and Table 250.66. |
| Neutral Conductor | The conductor connected to the neutral point of a system, transformer, or other device, intended to carry current under normal conditions. | In a 3-wire 120/240V single-phase service, the neutral is the grounded conductor. In 4-wire wye systems, the neutral carries unbalanced current. |
| Nominal Voltage | A nominal value assigned to a circuit or system for conveniently designating its voltage class (e.g., 120/240 V, 480Y/277 V). Actual voltage can vary within a range that permits satisfactory equipment operation. | Exam questions reference voltage classes (120, 240, 480) and you must pick the correct column in Table 310.16. |
| Ampacity | The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. | Drives every conductor-sizing question. Table 310.16 gives ampacities; correction factors (temperature) and adjustment factors (number of current-carrying conductors) modify them. |
| Continuous Load | A load where the maximum current is expected to continue for 3 hours or more. | Branch-circuit conductors and OCPD must be sized at 125% of the continuous load per 210.19(A)(1) and 210.20(A). |
| Dwelling Unit | A single unit providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation. | Triggers receptacle spacing rules in 210.52, GFCI in 210.8, AFCI in 210.12, and load calculations in 220 Part III. |
| Wet Location | Installations underground, in concrete slabs or masonry in direct contact with earth; locations subject to saturation with water or other liquids; and unprotected locations exposed to weather. | Requires rain-tight enclosures, sealed conduits, and appropriate conductor types (THWN, XHHW). |
| Damp Location | Partially protected locations subject to moderate degrees of moisture, such as some basements, some barns, some cold-storage warehouses. | Requires corrosion-resistant materials and drainage provisions. |
| Dry Location | A location not normally subject to dampness or wetness; may be temporarily subject to either, as in a building under construction. | Standard wiring methods (THHN, NM cable) are permitted. |
Critical Distinctions the Exam Targets
Grounded conductor vs. Equipment grounding conductor. This is the most-tested distinction on the exam. The grounded conductor (usually the neutral) is a current-carrying conductor under normal conditions; it is intentionally grounded at the service. The equipment grounding conductor is not a normal current carrier—it only carries fault current and its purpose is to bond metal parts and provide an effective ground-fault current path (250.4(A)(5)). The exam will ask which table sizes each: the grounded conductor is sized by 220.61 (neutral load) and 310.16; the EGC is sized by Table 250.122 based on the overcurrent device rating.
Branch circuit vs. Feeder. The key phrase is "final overcurrent device." Everything after the last breaker or fuse is a branch circuit (Article 210). Everything before it—running from the service equipment or transformer to that panelboard—is a feeder (Article 215). If a conductor goes from a 200-amp main breaker to a subpanel, and the subpanel contains the branch-circuit breakers, that conductor is a feeder.
Service vs. Separately derived system. A service comes from the utility. A separately derived system has no direct electrical connection to another source (other than grounding/bonding). A transformer with no grounded conductor passed through is a separately derived system. A generator with a transfer switch that breaks the neutral is also separately derived. The grounding rules differ: services ground at 250.24(C); separately derived systems ground at 250.30(A).
Continuous load and the 125% rule. When a load is continuous (3+ hours), the branch-circuit conductor and overcurrent device must be rated at not less than 125% of the continuous load (210.19(A)(1), 210.20(A)). If a continuous load is 16 A on a 20 A circuit: 16 × 1.25 = 20 A, so a 20 A breaker and 12 AWG conductor (20 A column, 60°C) work. But a 16 A continuous load on a 15 A circuit fails because 16 × 1.25 = 20 A > 15 A.
A conductor runs from a 200-amp service disconnect to a panelboard that contains 15- and 20-ampere branch-circuit breakers. Under NEC Article 100, this conductor is a:
Which statement correctly distinguishes a grounded conductor from an equipment grounding conductor under Article 100?
An electric vehicle charging area in a parking garage is subject to water saturation from pressure washing. Per Article 100, this area is classified as a: