Explanation of Demand Factors and Panel Calculations



Demand Factor

The demand factor is used in electrical calculations to reduce the total connected load to account for the fact that not all appliances or equipment operate simultaneously. It represents the ratio of the maximum expected load demand to the total connected load.

Panel Calculation

Panel calculations involve determining the load on a panelboard to ensure it can safely handle the electrical demand. The total load is calculated by multiplying the demand factor by the connected load for each circuit connected to the panelboard.

Reasons for Discrepancy Between NEC and Common Practice

The National Electrical Code (NEC) provides guidance on electrical installation practices, including recommended demand factors. However, industry practice may vary from the NEC recommendations based on various factors, such as:

Historical Data

Electrical loads have changed over time, and common practice may not have been updated to reflect these changes.

Safety Margin

Engineers and contractors often apply a higher demand factor than the NEC minimum to provide a safety margin and account for potential future load increases.

Experience and Industry Standards

Industry professionals have gained experience over time and established standards for certain types of installations, including restaurants.

Local Codes

Local codes may have different requirements than the NEC, which can also contribute to the discrepancy.

Specific Case of Restaurants

The NEC lists a demand factor of 100% for "other" occupancy types, which includes restaurants. However, industry practice has traditionally applied a demand factor of 125% for lighting in restaurants. This higher demand factor accounts for the heavy use of lighting in restaurant environments, including task lighting, ambient lighting, and decorative lighting. The increased load ensures that the panel can handle the expected demand without overloading.

Conclusion:

While the NEC recommends a demand factor of 100% for restaurants, common practice in the industry is to use a higher demand factor of 125% for lighting. This discrepancy is due to historical data, safety margins, industry experience, and local code requirements. It is important to consider these factors and consult with experienced electrical engineers when determining appropriate demand factors for specific installations. Flag for review