Table 220.3 of the National Electrical Code (NEC) provides a standardized method for calculating the electrical loads of a building. In this lesson, we will discuss how to use Table 220.3 to calculate the total connected load of a building.

Determine the Occupancy Classification The first step in using Table 220.3 is to determine the occupancy classification of the building. The occupancy classification is based on the primary use of the building, such as residential, commercial, or industrial.

Determine the Load Factor Once the occupancy classification has been determined, the next step is to find the load factor for that classification in Table 220.3. The load factor is a percentage that is used to calculate the total connected load of the building.

Calculate the Total Connected Load The final step is to multiply the load factor by the square footage of the building to calculate the total connected load. For example, if the load factor for a commercial building is 3 watts per square foot and the building has 10,000 square feet of space, the total connected load would be 30,000 watts or 30 kilowatts.

It is important to note that the total connected load calculated using Table 220.3 is the maximum expected load for the building and does not necessarily represent the actual load at any given time. The actual load will depend on the specific usage of the building and may be lower than the calculated load.

In addition, Table 220.3 is only one method for calculating electrical loads and may not be appropriate for all types of buildings or situations. It is important to consult the specific requirements of Article 220 of the NEC and to use professional judgment when calculating electrical loads.

Overall, Table 220.3 provides a standardized method for calculating the total connected load of a building based on the occupancy classification and square footage. By following the steps outlined above, it is possible to use Table 220.3 to calculate the maximum expected load for a building.

It’s important to note that Table 220.3 is updated every three years with each new edition of the NEC. Therefore, it’s important to use the most current version of the table to ensure accurate calculations.

In summary, using Table 220.3 of the NEC involves determining the occupancy classification of the building, finding the load factor for that classification in the table, and multiplying the load factor by the square footage of the building to calculate the total connected load. It is important to use professional judgment and consult the specific requirements of Article 220 of the NEC when calculating electrical loads.