Under the optional calculation method, four or more space-heating units are calculated at what percentage of their nameplate rating?

Under the optional calculation method, four or more space-heating units are calculated at what percentage of their nameplate rating?

• A. 100%
• B. 40%
• C. 65%
• D. 125%

Answer: (B)

The key idea is that the optional calculation method uses a reduced load for multiple space-heating units because they are unlikely to all run at full load at the same time. When there are four or more space-heating units, you estimate the load as 40% of their combined nameplate rating. This reflects diversity of operation and helps prevent oversizing feeders and the service. In other words, instead of adding 100% of each unit’s rating, you multiply the total by 0.4. The standard method would use 100% of the rating, so the 40% factor is what distinguishes the optional method and makes it the correct choice.

The key idea is that the optional calculation method uses a reduced load for multiple space-heating units because they are unlikely to all run at full load at the same time. When there are four or more space-heating units, you estimate the load as 40% of their combined nameplate rating. This reflects diversity of operation and helps prevent oversizing feeders and the service. In other words, instead of adding 100% of each unit’s rating, you multiply the total by 0.4. The standard method would use 100% of the rating, so the 40% factor is what distinguishes the optional method and makes it the correct choice.