Licensed Electrical Contractor Branch Circuit Calculations Questions and Answers

Question 1

A 120V branch circuit in a commercial office supplies a continuous lighting load of 13 amperes. What is the minimum required rating for the overcurrent protective device (OCPD) for this circuit?

Accepted Answer

20A

Answer

According to NEC 210.20(A), a branch circuit supplying continuous loads must have an overcurrent device rated for not less than 125% of the continuous load. The calculation is 13A * 1.25 = 16.25A. Since 16.25A is not a standard OCPD size listed in NEC 240.6(A), you must use the next higher standard size, which is 20A.

Question 2

What is the calculated load, in volt-amperes (VA), for a general-purpose branch circuit in a commercial building that supplies 12 duplex receptacles?

Accepted Answer

2,160 VA

Answer

NEC 220.14(I) specifies that for non-dwelling occupancies, each single or multiple receptacle on one yoke (strap) is calculated at a minimum of 180 VA. A duplex receptacle is on a single yoke. Therefore, the calculation is 12 receptacles * 180 VA/receptacle = 2,160 VA.

Question 3

A new single-family dwelling is being wired. Which of the following is a requirement for the small-appliance branch circuits serving the kitchen countertops?

Accepted Answer

A minimum of two 20-ampere circuits are required.

Answer

NEC 210.11(C)(1) and 210.52(B)(3) require that at least two 20-ampere small-appliance branch circuits be provided to supply the receptacle outlets serving the kitchen countertop surfaces in a dwelling unit. These circuits are not permitted to serve lighting or outlets in other areas like a garage.

Question 4

A conduit is installed containing eight current-carrying THHN/THWN copper conductors. According to NEC Table 310.15(C)(1), what adjustment factor must be applied to the ampacity of these conductors?

Accepted Answer

70%

Answer

NEC Table 310.15(C)(1) provides adjustment factors when there are more than three current-carrying conductors in a raceway or cable. For 7 to 9 current-carrying conductors, the table specifies that the allowable ampacity must be multiplied by an adjustment factor of 70%.

Question 5

What is the calculated branch-circuit demand load for a single 14 kW household electric range installed in a dwelling unit, using the standard calculation method?

Accepted Answer

8.8 kW

Answer

Per NEC Table 220.55, Column C, the demand load for one range rated not over 12 kW is 8 kW. Note 1 to the table states that for ranges over 12 kW through 27 kW, the demand load in Column C (8 kW) shall be increased by 5% for each additional kW over 12 kW. The range is 2 kW over 12 kW (14 kW - 12 kW = 2 kW). The increase is 2 * 5% = 10%. Therefore, the calculated load is 8 kW * 1.10 = 8.8 kW.

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Branch Circuit Calculations Questions and Answers