For dwellings, heating or A/C loads are calculated at ___% of the nameplate rating and the largest load is used for a standard calculation.

For dwellings, heating or A/C loads are calculated at ___% of the nameplate rating and the largest load is used for a standard calculation.

• A. 65
• B. 100
• C. 40
• D. 125

Answer: (B)

The main idea is that, when sizing a dwelling’s electrical service, the heating or cooling loads are taken at the full (100%) rated input of the equipment. This reflects the worst-case, peak demand from HVAC, so the service is sized to handle the largest possible load. Using the largest HVAC unit as the standard reference ensures you’re guarding against undersizing the service. Other loads (lighting, receptacles, etc.) are then accounted for with the usual diversity and demand factors, but the HVAC base is modeled at full nameplate rating because cooling or heating often drives the peak load. Options that reduce the percentage would understate the HVAC demand, and using more than 100% would exceed the equipment’s rating and isn’t appropriate. Therefore, the correct approach is 100%.

The main idea is that, when sizing a dwelling’s electrical service, the heating or cooling loads are taken at the full (100%) rated input of the equipment. This reflects the worst-case, peak demand from HVAC, so the service is sized to handle the largest possible load.

Using the largest HVAC unit as the standard reference ensures you’re guarding against undersizing the service. Other loads (lighting, receptacles, etc.) are then accounted for with the usual diversity and demand factors, but the HVAC base is modeled at full nameplate rating because cooling or heating often drives the peak load.

Options that reduce the percentage would understate the HVAC demand, and using more than 100% would exceed the equipment’s rating and isn’t appropriate. Therefore, the correct approach is 100%.