TN LLE Commercial Load Calculations 2 — Questions and Answers
Question 1: Per NEC 220.12, what is the general lighting load demand factor for the first 12,500 VA of commercial office space?
- 100% (Correct answer)
- 80%
- 50%
- 125%
Correct answer: 100%
Per NEC Table 220.42, the first 12,500 VA of general lighting for commercial occupancies uses a 100% demand factor.
NEC Table 220.42 provides demand factors for lighting loads. For commercial occupancies, the first 12,500 VA is calculated at 100% demand factor, meaning no reduction is applied. Only the portion of the lighting load exceeding 12,500 VA may be reduced to 50%. This ensures adequate capacity for the base lighting load while acknowledging that not all lighting in larger installations operates simultaneously.
Question 2: When calculating the service load for a commercial building, receptacle outlets are calculated at how many VA per outlet per NEC 220.14(I)?
- 90 VA
- 180 VA (Correct answer)
- 200 VA
- 150 VA
Correct answer: 180 VA
NEC 220.14(I) assigns 180 VA per receptacle outlet for general-purpose receptacles in commercial occupancies.
Per NEC 220.14(I), each general-purpose receptacle outlet in a non-dwelling occupancy is calculated at 180 VA. For multioutlet assemblies used in non-dwelling occupancies, each 5-foot section is calculated at 180 VA if not likely to be used simultaneously, or 180 VA per foot if simultaneous use is likely. This 180 VA value is fundamental to commercial load calculations.
Question 3: What is the demand factor applied to the first 10 kW of commercial kitchen equipment loads per NEC Table 220.56?
- 100%
- 80%
- 65%
- Demand factor depends on number of equipment units, not a fixed kW threshold (Correct answer)
Correct answer: Demand factor depends on number of equipment units, not a fixed kW threshold
NEC Table 220.56 provides demand factors for commercial kitchen equipment based on the number of units, not a fixed kW threshold.
NEC Table 220.56 establishes demand factors for commercial kitchen equipment based on the number of pieces of equipment. For 1-2 pieces the demand factor is 100%, 3 pieces is 90%, 4 pieces is 80%, 5 pieces is 70%, and 6 or more pieces allows a 65% demand factor. This recognizes that in commercial kitchens with multiple appliances, not all equipment operates at maximum load simultaneously.
Question 4: For a 10,000 sq ft commercial office, what is the minimum general lighting load before demand factors are applied?
- 10,000 VA
- 15,000 VA
- 35,000 VA
- It depends on the specific use designation in Table 220.12 (Correct answer)
Correct answer: It depends on the specific use designation in Table 220.12
The unit lighting load varies by occupancy type. NEC Table 220.12 assigns different VA per square foot values for different occupancy types.
NEC Table 220.12 lists different unit lighting loads (VA per square foot) based on occupancy type. For example, offices are 3.5 VA/sq ft, retail stores are 1.5 VA/sq ft, and warehouses are 0.25 VA/sq ft. For a 10,000 sq ft office at 3.5 VA/sq ft, the general lighting load would be 35,000 VA. The specific occupancy type must be identified before calculating the lighting load.
Question 5: When performing a commercial load calculation, the largest motor in the building gets what additional demand applied per NEC 220.50?
- No additional demand
- 25% of its full-load current added (Correct answer)
- 50% of its nameplate rating
- 100% of its locked-rotor current
Correct answer: 25% of its full-load current added
Per NEC 220.50, the feeder or service must include 25% of the highest-rated motor load in addition to the total calculated load.
NEC 220.50 requires that for services, feeders, and branch circuits, the calculated load includes 125% of the largest motor (or 25% added to the full-load current of the largest motor). This additional 25% accounts for the starting current demand of the largest motor. In commercial buildings with multiple motors, only the single largest motor receives this additional 25% — all other motors are included at 100% of their full-load current.
Question 6: A Tennessee LLE is calculating loads for a small retail space. Per NEC Table 220.12, what unit lighting load applies to a retail store?
- 3.5 VA per square foot
- 1.5 VA per square foot (Correct answer)
- 2.0 VA per square foot
- 1.0 VA per square foot
Correct answer: 1.5 VA per square foot
NEC Table 220.12 lists retail stores (other than listed types) at 1.5 VA per square foot for the general lighting load calculation.
NEC Table 220.12 assigns different unit lighting loads based on occupancy type. Retail stores are listed at 1.5 VA per square foot. This is lower than offices (3.5 VA/sq ft) because modern retail lighting is more efficient and not every area requires the same intensity. For a TN LLE working on a 2,000 sq ft retail space, the minimum general lighting load would be 2,000 x 1.5 = 3,000 VA before demand factors.
TN LLE Commercial Load Calculations 2
Per NEC 220.12, what is the general lighting load demand factor for the first 12,500 VA of commercial office space?