14.4 Commercial Building Load Capstone

Capstone Problem: 10,000 sq ft Office Building

This capstone integrates every rule from Sections 14.1 through 14.3 into a single end-to-end calculation.

Given:

• 10,000 sq ft office building
• 40 receptacle outlets (one per strap/yoke)
• Occupancy classification: office building, which triggers the 120.14(K) receptacle comparison
• Continuous display lighting: 2,000 VA (separate from Table 120.42(A) general lighting)
• Electric heating: 14,000 VA
• Air conditioning: 11,000 VA
• Commercial kitchen: range 4,000 VA + oven 3,000 VA (2 units)
• System: 208 V, three-phase

Step 1 — General Lighting (Table 120.42(A))

The 125% continuous load factor is already included in the Table 120.42(A) unit value — do not apply it again.

Step 2 — Receptacles (120.14(I), Table 120.47, and the 120.14(K) floor)

Two things are happening here. First, 7,200 VA is under the 10 kVA threshold, so no 50% reduction applies under Table 120.47. Second — and this is the step most candidates drop — 120.14(K) requires banks and office buildings to use the larger of the 120.14(I) result or 1 VA per square foot. At 10,000 ft² the floor is 10,000 VA, which beats the 7,200 VA strap count, so 10,000 VA is what moves forward. The two figures are never added.

Step 3 — Display Lighting Load

Include the known display lighting at 2000 VA in the Article 120 load sum. Under 120.5(E), the separate continuous-load sizing allowance is not added at this stage.

Step 4 — Noncoincident Loads (120.60)

Per 120.60, only the larger load is used. Per 120.51, fixed heating is calculated at 100% of connected load.

• Heating demand = 14,000 VA

Step 5 — Commercial Kitchen (Table 120.56)

Step 6 — Article 120 Load Sum

For a balanced 208 V three-phase supply:

I = 46,000 ÷ (208 × √3) = 127.7 A.

This is the load-calculation result. It is not yet a complete conductor or overcurrent-device selection. The display lighting is continuous, and fixed electric space heating has continuous-load sizing requirements. Apply the appropriate conductor/OCPD rules to those components, while avoiding double application of a factor already included in a table value. Check equipment nameplates, motor components and actual phase allocation before completing an installation design.

Step 7 — Separate Sizing Check

For this worked problem, assume the 14,000 VA heating component is fixed electric space heat, the separate 2000 VA display load is continuous, the table lighting already includes its applicable allowance, and the remaining demand components require no further continuous-load increase. The additional sizing allowance is 25% × (14,000 + 2000) = 4000 VA.

The sizing total is therefore 50,000 VA, giving 138.8 A at 208 V three-phase. With copper conductors, 75°C terminations, no adjustment or correction factors, and ordinary 80%-rated overcurrent equipment, 1/0 AWG copper at 150 A and a 150 A device satisfy this example. The 127.7 A load current and 138.8 A sizing current must not be confused.

What the Example Tests

• The office receptacle floor wins over the sparse 40-strap load.
• The smaller interlocked HVAC load is omitted; it is not added to heating.
• The Article 120 sum uses the known display load without an extra continuous-load multiplier.
• Conductor and OCPD selection then applies the separate sizing requirements.
• Balanced three-phase VA converts to line current using voltage times the square root of three, not voltage alone.

A different phase allocation, conductor temperature rating, ambient temperature, number of current-carrying conductors or equipment rating can change the final selection. Use all conditions stated in the exam question.