Licensed Electrical Contractor Wiring Methods and Materials Questions and Answers

Question 1

An electrical contractor is installing conductors in a raceway located on a rooftop where the ambient temperature is expected to reach 125°F (52°C). The design requires using 4/0 AWG THHN copper conductors. According to NEC Table 310.16, the ampacity of 4/0 THHN is 260A at 30°C. What is the corrected ampacity of these conductors after applying the required temperature correction factor from Table 310.15(B)(1)?

Accepted Answer

189.8A

Answer

According to NEC Table 310.15(B)(1), the correction factor for a 90°C rated conductor (like THHN) in an ambient temperature of 51-55°C (123-131°F) is 0.73. To find the corrected ampacity, you multiply the conductor's ampacity from Table 310.16 by this correction factor: 260A * 0.73 = 189.8A.

Question 2

When installing a multiconductor Type NM cable through a series of bored holes in wood studs, what is the minimum distance the edge of the hole must be from the nearest edge of the wood member to avoid the need for a protective steel plate?

Accepted Answer

1 1/4 inches

Answer

NEC Section 300.4(A)(1) requires that where cables are installed through bored holes in wood members, the holes shall be bored so that the edge of the hole is not less than 1 1/4 inches from the nearest edge of the wood member. If this distance cannot be maintained, a steel plate or bushing at least 1/16 inch thick must be installed to protect the cable.

Question 3

According to NEC Chapter 9, Table 1, what is the maximum permitted conduit fill percentage for a raceway containing three or more conductors?

Accepted Answer

40%

Answer

NEC Chapter 9, Table 1 specifies the allowable percentage of cross-sectional area of a conduit or tubing for conductors. For one conductor, the limit is 53%; for two conductors, it's 31%; and for over two conductors, the maximum permitted fill is 40%.

Question 4

A contractor is wiring a Class I, Division 1 hazardous location. Which of the following wiring methods is generally required to contain a potential explosion?

Accepted Answer

Threaded Rigid Metal Conduit (RMC) with explosion-proof fittings

Answer

NEC Article 501 specifies the requirements for Class I locations. In a Division 1 location, where flammable gases or vapors can exist under normal operating conditions, the wiring method must be able to contain an explosion. Threaded Rigid Metal Conduit (RMC) with appropriate explosion-proof fittings is the standard and required method to achieve this containment.

Question 5

Which of the following must be bonded together to create an effective ground-fault current path in a commercial installation using metallic cable trays?

Accepted Answer

All metallic cable tray sections, fittings, and the equipment grounding conductor system

Answer

According to NEC Article 250 and Article 392, metallic cable tray systems must be bonded to ensure electrical continuity. This involves bonding all metallic sections and fittings together to form a continuous path and connecting this system to the equipment grounding conductor to provide an effective ground-fault current path, which is essential for the operation of overcurrent protective devices.

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Wiring Methods and Materials Questions and Answers