Free TN-LLE Commercial Load Calculations Questions and Answers 1 — Questions and Answers
Question 1: What is the calculated general lighting load for a 20,000 sq. ft. office building after applying all applicable demand factors?
- 70,000 VA
- 41,250 VA (Correct answer)
- 35,000 VA
- 23,750 VA
Correct answer: 41,250 VA
First, calculate the total lighting VA: 20,000 sq. ft. x 3.5 VA/sq. ft. (Table 220.12) = 70,000 VA. Then, apply demand factors from Table 220.42: the first 12,500 VA is at 100%, and the remainder (57,500 VA) is at 50%. The final calculated load is 12,500 VA + (57,500 VA x 0.50) = 41,250 VA.
Question 2: A commercial occupancy has 100 general-purpose duplex receptacles. What is the calculated load for these receptacles after applying demand factors?
- 18,000 VA
- 9,000 VA
- 14,000 VA (Correct answer)
- 10,000 VA
Correct answer: 14,000 VA
Per NEC 220.14(I), each receptacle outlet is calculated at 180 VA. The total connected load is 100 outlets x 180 VA = 18,000 VA. According to NEC 220.44, the first 10 kVA (10,000 VA) is taken at 100%, and the remainder (8,000 VA) is at 50%. The calculated load is 10,000 VA + (8,000 VA x 0.50) = 14,000 VA.
Question 3: What is the calculated load for 40 linear feet of show-window lighting in a retail store?
- 4,000 VA
- 6,000 VA
- 8,000 VA (Correct answer)
- 10,000 VA
Correct answer: 8,000 VA
NEC 220.14(G) requires that show-window lighting be calculated at a minimum of 200 VA per linear foot. Therefore, the total calculated load is 40 ft x 200 VA/ft = 8,000 VA. This load is added to the general lighting load before general lighting demand factors are applied.
Question 4: A commercial kitchen contains 5 pieces of permanently installed cooking equipment with a total nameplate rating of 60 kW. What is the calculated demand load for this equipment?
- 60 kW
- 42 kW (Correct answer)
- 39 kW
- 48 kW
Correct answer: 42 kW
NEC 220.56 and the associated Table 220.56 allow for a demand factor to be applied to commercial kitchen equipment. For 5 appliances, the demand factor is 70%. The calculated load is 60 kW x 0.70 = 42 kW.
Question 5: A 4-wire, 3-phase, 208Y/120V system serves a non-linear load with a calculated maximum unbalanced current of 250A. What is the calculated demand load on the neutral conductor?
- 250A
- 200A
- 175A
- 235A (Correct answer)
Correct answer: 235A
According to NEC 220.61(C), a demand factor of 70% can be applied to the portion of the unbalanced load exceeding 200A. The first 200A is calculated at 100%. The calculation is: 200A + ((250A - 200A) x 0.70) = 200A + (50A x 0.70) = 200A + 35A = 235A.
Question 6: What is the feeder demand load for fixed electric space heating in a commercial building with three units rated at 5 kW, 6 kW, and 10 kW?
- 10 kW
- 15.75 kW
- 21 kW (Correct answer)
- 16.8 kW
Correct answer: 21 kW
According to NEC 220.51, the load for fixed electric space heating is calculated at 100% of the total connected load. There are no demand factors for commercial space heating unless specific conditions for diversity are met, which are not mentioned here. The total load is 5 kW + 6 kW + 10 kW = 21 kW.
Free TN-LLE Commercial Load Calculations Questions and Answers 1
What is the calculated general lighting load for a 20,000 sq. ft. office building after applying all applicable demand factors?