Step 1: Determine the total number of watts for the general lighting.
- Assume an average of 1.5 watts per square foot for general lighting in a school.
- Multiply the total square footage of the school by 1.5 watts per square foot.
Step 2: Determine the total number of watts for the receptacles.
- Assume an average of 180 VA (volt-amperes) per receptacle.
- Multiply the number of receptacles by 180 VA.
Step 3: Calculate the total load in watts.
- Add the total number of watts for general lighting and the total number of watts for receptacles.
Step 4: Calculate the feeder load.
- Apply a diversity factor of 0.8 to the total load in watts.
- The diversity factor accounts for the fact that not all lights and receptacles will be operating simultaneously.
For example, if the school has a total area of 10,000 square feet and 157 receptacles, the general lighting and feeder load calculations would be as follows:
Step 1: General lighting load
Total square footage = 10,000 square feet
General lighting load = 10,000 square feet * 1.5 watts/square foot = 15,000 watts
Step 2: Receptacles load
Number of receptacles = 157
Receptacles load = 157 receptacles * 180 VA/receptacle = 28,260 VA
Step 3: Total load
Total load = General lighting load + Receptacles load
Total load = 15,000 watts + 28,260 VA = 43,260 VA
Step 4: Feeder load
Feeder load = Total load * Diversity factor
Feeder load = 43,260 VA * 0.8 = 34,608 VA
Therefore, the NEC calculated general lighting and feeder load for a 2-story school with 157 receptacles would be 34,608 VA.