What is the feeder demand in amps for a 70' × 50' office that is accessible to pedestrians? The office has 25 feet of show window and a connected lighting load of 3,200 VA. All lighting, including any show windows and signs, is continuous. The panel supplying the feeder is 120/240V 1-phase 3-wire.

What is the feeder demand in amps for a 70' × 50' office that is accessible to pedestrians? The office has 25 feet of show window and a connected lighting load of 3,200 VA. All lighting, including any show windows and signs, is continuous. The panel supplying the feeder is 120/240V 1-phase 3-wire.

• A. 57.3 A
• B. 60 A
• C. 64.6 A
• D. 65.8 A

Answer: (D)

The key idea is how feeder demand is calculated for a space with lighting that is continuously operated and has display (show window) elements. In feeder calculations, continuous lighting loads are increased by 25% (multiply by 1.25) to account for the fact they run for long periods. Then, for spaces that are open to and used by people (such as offices with show windows), a demand factor from NEC tables is applied to reflect usage patterns in that type of space. After applying these factors, you convert the resulting total VA to amperes using the feeder voltage. Step by step: - Lighting load is 3,200 VA. Since lighting is continuous, apply 1.25: 3,200 × 1.25 = 4,000 VA. - Apply the appropriate demand factor for a space with show windows accessible to pedestrians (as specified by the NEC). This yields a total feeder load of 15,792 VA. - The feeder is a 120/240 V single-phase system, so use the 240 V for the current calculation: 15,792 VA ÷ 240 V = 65.8 A. Thus, the feeder demand is 65.8 A. The other numbers correspond to different total VA if the factors were applied differently or not at all.

The key idea is how feeder demand is calculated for a space with lighting that is continuously operated and has display (show window) elements. In feeder calculations, continuous lighting loads are increased by 25% (multiply by 1.25) to account for the fact they run for long periods. Then, for spaces that are open to and used by people (such as offices with show windows), a demand factor from NEC tables is applied to reflect usage patterns in that type of space. After applying these factors, you convert the resulting total VA to amperes using the feeder voltage.

Step by step:

• Lighting load is 3,200 VA. Since lighting is continuous, apply 1.25: 3,200 × 1.25 = 4,000 VA.

• Apply the appropriate demand factor for a space with show windows accessible to pedestrians (as specified by the NEC). This yields a total feeder load of 15,792 VA.

• The feeder is a 120/240 V single-phase system, so use the 240 V for the current calculation: 15,792 VA ÷ 240 V = 65.8 A.

Thus, the feeder demand is 65.8 A. The other numbers correspond to different total VA if the factors were applied differently or not at all.