ICC G21 Low-Voltage Electrician Exam (2017 NEC) Practice Exam
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- 50 questions (same as real exam)
- 180 minute time limit
- 5 topic areas covered
- 226 questions in pool
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ICC G21 Low-Voltage Electrician (2017 NEC) Practice Exam Guide
What's on the exam
Questions per topic, out of 50This practice exam is laid out like the official content outline for the ICC G21 Low-Voltage Electrician (2017 NEC) exam: General Knowledge, LV Remote Control & Alarm Systems, LV Communications & Sound, LV Control Circuits, Fiber Optical.
Two ways to practice: the free practice exam gives you 10 questions per attempt, as often as you want. The full practice exam gives you 50 questions on a 3 hours clock, with a new draw from our question bank every time.
General Knowledge 12 items
Our study plan for this topic: Ohm's Law and power formulas (P, E, I, R relationships); Series, parallel, and combination circuit calculations; AC circuit concepts: impedance, reactance, inductance, and capacitance; Electrical formulas for amperes, kilowatts, kVA, and horsepower (single-phase and three-phase); Grounding and bonding principles and terminology (NEC Article 250); NEC code structure, scope, definitions, and general installation requirements; Power factor, power factor correction, and efficiency calculations; Electrical symbols, field terms vs. NEC terms, and units of measurement/conversion.
LV Remote Control & Alarm Systems 11 items
Our study plan for this topic: Class 1 vs. Class 2 vs. Class 3 circuit classifications and definitions; Power source requirements for Class 2 and Class 3 circuits; Class 1 circuit overcurrent protection and conductor sizing; Separation of Class 2/Class 3 circuits from power and Class 1 conductors; Cable types and substitution hierarchy for Class 2, Class 3, and PLTC cables; Fire alarm circuit classifications: NPLFA vs. PLFA; Power source and branch circuit requirements for fire alarm systems; Fire alarm cable types, listing requirements, and installation by building location.
LV Communications & Sound 18 items
Our study plan for this topic: Communications cable types and listing requirements (CMP, CMR, CMG, CM, CMX, CMUC); Cable installation locations — plenums, risers, and general-purpose spaces (Article 800); Grounding and bonding of communications cables and primary protectors (Article 800); Primary and secondary protectors — application, location, and types; CATV coaxial cable types, installation, and grounding of outer conductive shield (Article 820); Network-powered broadband communications systems — power classifications, cable types, and installation (Article 830); Audio signal processing and reproduction equipment — wiring methods, grounding, and loudspeaker installation (Article 640); Radio and television antenna systems — materials, clearances, discharge units, and bonding conductors (Article 810).
LV Control Circuits 7 items
Our study plan for this topic: Motor control circuit overcurrent protection and conductor sizing (NEC 430.72); Electrical arrangement and grounding of control circuits (NEC 430.74); Disconnection of motor control circuits from all power sources (NEC 430.75); Class 1 vs. Class 2 vs. Class 3 remote-control circuit classifications and power source requirements; Three-wire stop-start station wiring and seal-in contact operation; Multiple stop-start stations and hand-off-automatic (HOA) control circuit configurations; Jogging circuits and control relay wiring for inching operations; Control circuit transformer protection and reduced-voltage control wiring methods.
Fiber Optical 2 items
Our study plan for this topic: Optical fiber cable types and listing requirements (OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, OFC); Installation locations within buildings (plenums, risers, general spaces, cable trays); Grounding and bonding of metallic members of optical fiber cables; Separation requirements when installed with electrical conductors; Overhead and underground optical fiber cables entering buildings; Cable substitution hierarchy for optical fiber cable types; Abandoned optical fiber cable requirements and fire spread prevention; Unlisted optical fiber cables entering buildings (50 ft rule, raceway requirements).
Sample 1 — LV Communications & Sound
Question: You are installing Type CMX communications cable less than 6 mm (0.25 in.) in diameter in a multifamily apartment building, in building locations other than ducts, plenums, risers, cable trays, and distributing frames. Where is this cable permitted?
- A. In concealed spaces behind finished walls
- B. In plenum cable routing assemblies
- C. In nonconcealed spaces
- D. In riser shafts penetrating floors
Correct Answer: C
NEC 800.113(K)(2) permits Type CMX cables less than 6 mm (0.25 in.) in diameter in multifamily dwellings only in nonconcealed spaces. Risers, plenum assemblies, and concealed spaces require higher-rated cable types such as CM, CMG, CMR, or CMP.
Reference: NEC 2017 Section 800.113(K)
Sample 2 — General Knowledge
Question: The grounding electrode conductor size for alternating-current systems is determined by the size of the largest ______ conductor or equivalent area for parallel conductors.
- A. Equipment grounding
- B. Grounded (neutral)
- C. Ungrounded
- D. Bonding jumper
Correct Answer: C
Per NEC Table 250.66, the grounding electrode conductor for AC systems is sized based on the size of the largest ungrounded conductor or equivalent area for parallel conductors. This table correlates the ungrounded service conductor size to the required grounding electrode conductor size.
Reference: NEC 2017 Section 250.66 / Table 250.66
Sample 3 — LV Remote Control & Alarm Systems
Question: Which cable type is a permitted substitution for Type FPL power-limited fire alarm cable?
- A. CL3P
- B. PLTC
- C. NPLF
- D. FPLR
Correct Answer: D
Table 760.154(A) permits Types CMP, FPLP, CMR, FPLR, CMG, and CM as substitutions for Type FPL. Non–power-limited (NPLF), power-limited tray cable (PLTC), and Class 3 plenum (CL3P) cables are not listed substitutions for fire alarm FPL cable.
Reference: NEC 2017 Table 760.154(A)
Your first attempt is an inspection, not a final grade. The results page breaks your score down by outline topic, so you can see which areas need work. Compare it with the real exam's passing score, 70% correct, and keep practicing until you pass consistently.
- Answer what you know first and bookmark the rest. Our practice exams let you bookmark and come back.
- Work your bookmarks on the second pass.
- Keep your pace. The real exam works out to about 3 minutes 36 seconds per question.
- After each attempt, look up each missed question's reference in your book and read the section.
| Questions | 50 questions |
| Time limit | 3 hours |
| Passing score | 70% correct |
| Books in the exam room | Open book |
| Exam fee | $120 |
- Results for examinations taken electronically are available immediately after the examination is completed.
- You must wait 10 days before retaking a failed exam.
Source: National Contractor/Trades Examination Information Bulletin, PUBLISHED June 30, 2026; ICC Exam Catalog, checked September 27, 2026. Check the bulletin before test day: fees and rules can change.