PC - Professional Electrical Contractor Wiring Methods and Protection Questions and Answers

Question 1

According to NEC Article 240, what is the standard maximum overcurrent protection permitted for a 12 AWG copper conductor used in a residential branch circuit?

Accepted Answer

20 amperes

Answer

NEC Section 240.4(D)(5) specifically limits the overcurrent protection for 12 AWG copper conductors to 20 amperes. This rule is in place to prevent overheating of conductors commonly used in residential branch circuits and applies regardless of the conductor's insulation temperature rating.

Question 2

An electrician is installing a feeder in a commercial building. The conductors will be run in a raceway where all conductors of the same circuit must be grouped together. Which NEC Article provides the general requirements for this installation practice?

Accepted Answer

Article 300

Answer

NEC Article 300 covers the general requirements for wiring methods and materials. Specifically, Section 300.3(B) mandates that all conductors of the same circuit, including the equipment grounding conductor and neutral conductor, must be contained within the same raceway, cable, or trench to minimize inductive heating and maintain circuit integrity.

Question 3

A new installation requires running Type UF cable underground to supply an outdoor receptacle. The circuit is 120V and protected by a 20A GFCI circuit breaker at its source. What is the minimum required burial depth for the Type UF cable under a residential lawn?

Accepted Answer

12 inches

Answer

According to NEC Table 300.5, Column 4, for residential branch circuits rated 120 volts or less with GFCI protection and a maximum overcurrent protection of 20 amperes, the minimum cover requirement for Type UF cable is 12 inches.

Question 4

Which of the following wiring methods is NOT permitted for use in a Class I, Division 1 hazardous location?

Accepted Answer

Electrical metallic tubing (EMT)

Answer

NEC Article 501.10(A) lists the approved wiring methods for Class I, Division 1 locations. These include threaded rigid metal conduit, threaded steel intermediate metal conduit, and Type MI cable. Electrical Metallic Tubing (EMT) is not permitted in these highly hazardous areas due to its non-threaded fittings, which cannot reliably prevent the passage of hot gases in an explosion.

Question 5

In a commercial installation, a 400A feeder is tapped to supply a 100A panelboard. The tap conductors are 15 feet long and are installed in a raceway. According to the NEC feeder tap rules, what is the minimum required ampacity for these tap conductors?

Accepted Answer

133A (1/3 of feeder OCPD)

Answer

Per NEC 240.21(B)(2), for feeder taps not over 25 feet long, the tap conductors must have an ampacity of not less than 1/3 of the rating of the overcurrent protective device protecting the feeder conductors. In this case, 400A / 3 = 133.3A. The tap conductors must also have an ampacity not less than the rating of the termination device (100A). Since 133.3A is greater than 100A, the minimum ampacity for the tap conductors is 133.3A, which would necessitate a conductor size with an ampacity meeting or exceeding this value.

(PC) Professional Electrical Contractor Practice Test

(PC) Professional Electrical Contractor Practice Test

PC - Professional Electrical Contractor Wiring Methods and Protection Questions and Answers