Journeyman/Master Electrician License Exam National Electrical Code Navigation and General Requirements Flashcards

24 sample cards from the National Electrical Code Navigation and General Requirements deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Per Article 240.21, where overcurrent protection is generally required for conductors, and what is the basic 'tap rule' concept?

   Overcurrent protection is generally required at the point where the conductor receives its supply (the point of supply). Tap conductors (smaller conductors connected to a larger feeder) are permitted without overcurrent protection at the tap point under specific conditions — the 10-foot tap rule (240.21(B)(1)) and 25-foot tap rule (240.21(B)(2)) being the most common.

2. State the 10-foot tap rule conditions (Article 240.21(B)(1)).

   Tap conductors up to 10 ft long need no overcurrent device at the tap if: they do not extend beyond the equipment/enclosure they supply, their ampacity is not less than the load and not less than the rating of the device/conductors they supply, they are enclosed in a raceway (if leaving the enclosure), and the ampacity is at least 10% of the feeder overcurrent device rating protecting the larger conductor.

3. State the 25-foot tap rule conditions (Article 240.21(B)(2)).

   Tap conductors up to 25 ft long need no overcurrent device at the tap if: the tap conductor ampacity is at least one-third (1/3) the rating of the overcurrent device protecting the feeder, they terminate in a single overcurrent device rated no more than the tap conductor ampacity, and they are protected from physical damage or enclosed in a raceway.

4. What temperature columns appear in Table 310.16, and which one is most commonly used for terminations on equipment rated over 100 A?

   Table 310.16 has three insulation temperature columns: 60°C, 75°C, and 90°C. The 75°C column is most commonly used for equipment terminations rated over 100 A. The 90°C column is generally used only for derating/adjustment calculations, not for final termination ampacity.

5. Per Article 310.15(C)(1), when must conductor ampacity be adjusted for the number of current-carrying conductors, and what is the adjustment factor for 4-6 conductors?

   Ampacity adjustment applies when more than 3 current-carrying conductors are bundled or in a raceway for more than $600\text{ mm}$ ($24\text{ in}$). For 4-6 current-carrying conductors, the adjustment factor is 80%; for 7-9 it is 70%; for 10-20 it is 50%.

6. How is the neutral (grounded) conductor counted as a current-carrying conductor for ampacity adjustment per Article 310.15(E)?

   A neutral carrying only the unbalanced current from other conductors is NOT counted as current-carrying. However, the neutral of a 3-wire circuit from a 4-wire wye system, or where the major portion of the load is nonlinear (harmonic) so the neutral carries current, IS counted as a current-carrying conductor.

7. What is the fundamental purpose distinction between 'grounding' and 'bonding' in Article 250?

   Grounding connects a system or equipment to the earth (or to a conductive body serving in place of earth) to stabilize voltage and provide a path for lightning/fault currents to ground. Bonding connects metallic parts together to establish electrical continuity and conductivity, ensuring a low-impedance fault-current path so overcurrent devices operate.

8. Per Article 250, what are the five primary purposes of system and equipment grounding?

   (1) Limit voltages from lightning, line surges, or unintentional contact with higher-voltage lines; (2) stabilize voltage to earth during normal operation; (3) for equipment, limit voltage on metal parts to ground; (4) provide a low-impedance path to facilitate operation of overcurrent devices during a ground fault; and (5) provide a safe effective ground-fault current path.

9. What is the definition and required characteristics of the 'effective ground-fault current path' per Article 250.4(A)(5)?

   It is an intentionally constructed, low-impedance, electrically conductive path designed to carry the maximum ground-fault current likely to be imposed from any point on the wiring system to the electrical supply source. It must facilitate the operation of the overcurrent device. The earth itself must NOT be used as the sole effective ground-fault current path.

10. Per Article 250.50 and 250.52, name the electrodes that make up the grounding electrode system.

    All of the following present must be bonded together: metal underground water pipe (in contact with earth 10 ft or more), metal in-ground support structure (footing/Ufer), concrete-encased electrode (rebar/wire), ground ring, rod and pipe electrodes, plate electrodes, and other listed/local metal underground systems. If none are present, one or more made electrodes must be installed.

11. Per Article 250.53(G), what is the required minimum depth of installation for a driven ground rod electrode, and what length must it be?

    A rod electrode must be at least $2.44\text{ m}$ ($8\text{ ft}$) in length and must be driven so that at least $2.44\text{ m}$ ($8\text{ ft}$) is in contact with the soil. It is typically driven vertically; if rock bottom is encountered it may be driven at up to 45 degrees or buried in a trench at least $750\text{ mm}$ ($30\text{ in}$) deep.

12. Per Article 250.53(A)(2), what is the 'single rod' supplemental electrode rule and the 25-ohm requirement?

    A single rod, pipe, or plate electrode that does not have a resistance to ground of $25\ \Omega$ or less must be supplemented by one additional electrode. If two rods are used, they must be spaced at least $1.8\text{ m}$ ($6\text{ ft}$) apart. (Installing two rods is the common way to avoid having to measure resistance.)

13. How is the grounding electrode conductor (GEC) sized per Table 250.66, and what is the maximum required size when connecting to a rod/pipe/plate electrode?

    The GEC is sized from Table 250.66 based on the largest ungrounded service-entrance conductor. However, per 250.66(A), the portion connecting to a rod, pipe, or plate electrode is never required to be larger than 6 AWG copper (4 AWG aluminum); to a concrete-encased electrode, never larger than 4 AWG copper; to a ground ring, not larger than the ring conductor.

14. How is the equipment grounding conductor (EGC) sized per Table 250.122, and what governs the selection?

    The EGC is sized from Table 250.122 based on the rating or setting of the overcurrent device (fuse/breaker) ahead of the equipment, NOT the conductor size directly. Example: a 60 A circuit requires a minimum 10 AWG copper EGC; a 100 A circuit requires 8 AWG copper; a 200 A circuit requires 6 AWG copper.

15. Per Article 250.122(B), when ungrounded conductors are increased in size (e.g., for voltage drop), what must happen to the equipment grounding conductor?

    When ungrounded conductors are increased in size from the minimum (for voltage drop or any reason), the wire-type equipment grounding conductors must be increased in size proportionally according to the circular mil area of the ungrounded conductors.

16. Per Article 250.24, at a service, where is the grounded (neutral) conductor connected to the equipment/grounding, and what is the main bonding jumper?

    At the service, the grounded (neutral) conductor is bonded to the service equipment enclosure and the equipment grounding conductor by the MAIN BONDING JUMPER. This is the only point (in a typical system) where the neutral and ground are intentionally connected. The grounding electrode conductor also connects here.

17. Per Article 250.28, how is the main bonding jumper (and system bonding jumper) sized?

    The main bonding jumper and system bonding jumper are sized per Table 250.102(C)(1), based on the size of the largest ungrounded service-entrance/derived conductor. Where the supply conductors exceed 1100 kcmil copper, the jumper must be at least 12.5% of the area of the largest phase conductor.

18. Per Article 250.104(A), how must metal water piping systems in a building be bonded?

    The metal water piping system must be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor (if of sufficient size), or to one or more grounding electrodes. The bonding jumper is sized per Table 250.102(C)(1) based on the service conductor size.

19. Per Article 250.104(B), how is bonding of 'other metal piping' such as gas piping handled?

    Metal piping systems (e.g., gas, other) that may become energized must be bonded to the equipment grounding conductor of the circuit likely to energize the piping, the service equipment enclosure, the grounded conductor at the service, the GEC, or a grounding electrode. The bonding jumper is sized per Table 250.122 using the rating of the circuit likely to energize the piping.

20. What is the difference between a grounded conductor, a grounding conductor, and a grounding electrode conductor per Article 100?

    A grounded conductor is a system conductor intentionally grounded — usually the neutral, normally carrying current. An equipment grounding conductor (EGC) is the conductive path connecting non-current-carrying metal parts to ground/source, normally carrying NO current. A grounding electrode conductor (GEC) connects the grounding electrode(s) to the grounded conductor and/or EGC at the service or source.

21. Per Article 250.118, name at least four wiring methods or items recognized as equipment grounding conductors.

    Acceptable EGCs include: a copper/aluminum wire (bare or insulated); rigid metal conduit (RMC); intermediate metal conduit (IMC); electrical metallic tubing (EMT); the armor of Type AC cable; the combined metallic sheath/EGC of Type MC cable; flexible metal conduit (FMC) and liquidtight FMC under listed length/size limits; and metal raceways/cable trays meeting listing requirements.

22. Per Article 230.42, how are service-entrance conductors sized relative to the load, including continuous loads?

    Service-entrance conductors must have an ampacity not less than the noncontinuous load plus 125% of the continuous load (or the load per 220 calculation): $$I_{SE} \geq I_{noncontinuous} + 1.25 \times I_{continuous}$$ The conductors must not be smaller than the rating of the service disconnecting means as required.

23. Per the optional 310.12 rule, what reduced ampacity is permitted for 120/240 V, single-phase dwelling service and feeder conductors?

    For an individual dwelling unit's main power feeder or service conductors (120/240 V, 3-wire, single-phase), the conductors are permitted to have an ampacity not less than 83% of the service/feeder rating. For example, a 200 A service requires $0.83 \times 200 = 166\text{ A}$, allowing 4/0 AWG aluminum or 2/0 AWG copper at 75°C.

24. What is the general voltage drop recommendation in the NEC for branch circuits and feeders, and is it mandatory?

    The NEC recommends (in Informational Notes, e.g., 210.19 and 215.2) that the voltage drop on a branch circuit not exceed 3%, and the combined branch circuit plus feeder not exceed 5%, of the nominal voltage for reasonable efficiency. Because it appears in Informational Notes, it is a recommendation, NOT a mandatory requirement (except in specific cases like fire pumps or sensitive equipment).

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