SEO Electrical Systems & Wiring 3 — Questions and Answers
Question 1: What is the minimum depth of burial required for UF (underground feeder) cable used for residential outdoor wiring per NEC?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
NEC Table 300.5 requires UF cable to be buried a minimum of 24 inches, though 12 inches is allowed under certain conduit conditions.
Question 2: In a 240V residential circuit for a dryer, what color combination of hot wires is used?
- Black and white
- Black and red (Correct answer)
- Red and green
- White and green
Correct answer: Black and red
240V circuits use two ungrounded (hot) conductors, typically black and red, each carrying 120V to neutral for a combined 240V.
Question 3: What is the primary purpose of bonding in an electrical system?
- Increase circuit voltage
- Ensure all metal parts are at the same electrical potential to prevent shock (Correct answer)
- Reduce circuit amperage
- Improve insulation quality
Correct answer: Ensure all metal parts are at the same electrical potential to prevent shock
Bonding connects all metal components to maintain equal potential, so no dangerous voltage difference exists between touchable metal surfaces.
Question 4: Which NEC article primarily governs wiring methods and materials for general use?
- Article 100
- Article 200
- Article 300 (Correct answer)
- Article 500
Correct answer: Article 300
NEC Article 300 covers general requirements for all wiring methods including installation, protection, and conductor fill.
Question 5: What does a three-way switch circuit allow you to do?
- Control a light from two different locations (Correct answer)
- Run three separate light fixtures from one switch
- Operate a 240V appliance
- Dim a light to three brightness levels
Correct answer: Control a light from two different locations
A three-way switch configuration uses two switches and a traveler wire pair, allowing a light to be controlled from two separate locations.
Question 6: What is 'voltage drop' and why is it significant in long wire runs?
- A safety feature that cuts power during surges
- The reduction in voltage along a conductor due to its resistance, reducing efficiency and device performance (Correct answer)
- A scheduled reduction in utility power during peak hours
- The voltage difference between hot and neutral in a 240V circuit
Correct answer: The reduction in voltage along a conductor due to its resistance, reducing efficiency and device performance
Voltage drop occurs because wire resistance dissipates energy; NEC recommends keeping it below 3% for branch circuits to ensure proper device operation.
Question 7: Which wiring method uses individual conductors pulled through metal or PVC tubing for protection?
- NM cable (Romex)
- Conduit wiring (Correct answer)
- BX armored cable
- Service entrance cable
Correct answer: Conduit wiring
Conduit wiring routes individual THHN or THWN conductors through EMT, IMC, or PVC conduit, offering superior physical protection and rewirability.
SEO Electrical Systems & Wiring 3
What is the minimum depth of burial required for UF (underground feeder) cable used for residential outdoor wiring per NEC?