IEC Basic Electrical Standards 5 — Questions and Answers
Question 1: Per the NEC, what is the maximum rating of a single overcurrent device that may protect a multi-wire branch circuit shared by two ungrounded conductors?
- 15 amperes
- 20 amperes (Correct answer)
- 30 amperes
- No limit, as long as each conductor is protected individually
Correct answer: 20 amperes
NEC 210.4 requires multi-wire branch circuits to have a means to disconnect all ungrounded conductors simultaneously, and each conductor must be protected at its ampacity.
Question 2: When is an arc-fault circuit interrupter (AFCI) required for bedroom circuits in a new residential installation?
- Only for circuits with aluminum wiring
- For all 15- and 20-ampere, 120-volt branch circuits (Correct answer)
- Only for circuits over 20 amperes
- Only when the homeowner requests it
Correct answer: For all 15- and 20-ampere, 120-volt branch circuits
NEC 210.12 requires AFCI protection for all 15- and 20-ampere, 120-volt branch circuits in dwelling unit bedrooms.
Question 3: What is the NEC requirement for securing nonmetallic sheathed cable (NM) within how many inches of a metal box?
- 6 inches
- 8 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
NEC 334.30 requires NM cable to be secured within 12 inches of every metal box or fitting.
Question 4: A 240-volt, single-phase motor draws 18 amperes at full load. What is the minimum size inverse-time circuit breaker permitted for branch circuit protection per NEC?
- 20 amperes
- 30 amperes
- 40 amperes
- 45 amperes (Correct answer)
Correct answer: 45 amperes
NEC 430.52 allows inverse-time breakers to be sized up to 250% of FLC; 18A × 250% = 45A, which is a standard size.
Question 5: Under NEC 110.3(B), what is required after installing any listed electrical equipment?
- A third-party inspection must be performed
- The equipment must be used only within its listing and labeling instructions (Correct answer)
- The manufacturer must be notified of the installation
- A warranty card must be filed with the AHJ
Correct answer: The equipment must be used only within its listing and labeling instructions
NEC 110.3(B) mandates that listed or labeled equipment be installed and used in accordance with its listing and labeling instructions.
Question 6: What is the minimum headroom required in the working space in front of electrical service equipment rated 200 amperes or less in a dwelling?
- 5.5 feet
- 6 feet
- 6.5 feet (Correct answer)
- 7 feet
Correct answer: 6.5 feet
NEC 110.26(A)(3) requires a minimum headroom of 6.5 feet in the working space in front of electrical equipment.
Question 7: Which of the following best describes a 'listed' electrical product as referenced in the NEC?
- A product approved solely by the local AHJ
- Equipment included in a list published by an OSHA-recognized testing laboratory (Correct answer)
- Any product that has a manufacturer's label
- Equipment approved by the NEC committee
Correct answer: Equipment included in a list published by an OSHA-recognized testing laboratory
NEC Article 100 defines 'listed' as equipment included in a list published by a nationally recognized testing laboratory (NRTL).
IEC Basic Electrical Standards 5
Per the NEC, what is the maximum rating of a single overcurrent device that may protect a multi-wire branch circuit shared by two ungrounded conductors?