Calculating commercial electrical load means determining the total electrical demand a building will place on its system, by adding up the connected loads, applying code-defined demand factors and the continuous-load rule, and arriving at a calculated load used to size the service, feeders, and equipment. This is a code-governed engineering calculation, not a simple sum, because code specifies how different loads are counted. Understanding the general approach helps business owners see how their service is sized, while the calculation itself is done by professionals.

Here is how commercial electrical load is calculated.

Commercial load calculations are detailed, code-governed procedures that vary by occupancy and load type, so they are performed by qualified electricians or engineers following the applicable code.

It is a code-governed calculation

A commercial load calculation is not just adding up wattages; it follows the methods defined in the electrical code, which specify how each type of load is counted and what factors apply. The code provides the rules for calculating loads for different occupancies and load types, so the result is a code-compliant calculated load. This is why the calculation is a defined engineering procedure rather than a rough estimate.

Start with the connected loads

The calculation starts by identifying and summing the building’s connected loads, all the electrical loads the building will have, such as:

• Lighting
• Receptacle loads
• HVAC and motors
• Appliances and equipment
• Special and specific loads

This establishes the total connected load before code factors are applied, as the starting point for the calculation.

Apply demand factors

Because not all loads run at full capacity simultaneously, the code allows demand factors to be applied to certain loads, reducing them from their full connected value to a realistic demand value. Demand factors reflect that, for example, not every receptacle or all of certain loads will draw maximum power at once. Applying the code’s demand factors to the applicable loads turns the connected load into a more realistic calculated demand, which is a key part of the calculation.

Apply the continuous-load rule

The calculation also accounts for continuous loads, those expected to run for extended periods, which code requires to be counted at 125 percent of their value for sizing purposes. This is the opposite of a reduction: continuous loads are increased in the calculation to ensure the system is not sized too tightly for loads that run constantly. Properly handling continuous loads at 125 percent is an important part of a correct load calculation.

Arrive at the calculated load

Combining the connected loads, the demand factors, and the continuous-load treatment yields the calculated load, the figure used to size the service, feeders, panels, and equipment. This calculated load ensures the system has adequate capacity for the building’s realistic demand with appropriate margins, without being oversized wastefully or undersized dangerously. Because it involves code rules and judgment, the calculation is performed by qualified electricians or engineers, who then size the system from it.

Calculating commercial electrical load means determining the building’s total electrical demand by summing the connected loads, applying code-defined demand factors to reduce loads that do not all run at once, applying the continuous-load rule that counts continuous loads at 125 percent, and arriving at a calculated load used to size the service and equipment. It is a detailed, code-governed procedure performed by qualified professionals, and it ensures the system has adequate, appropriate capacity.

Stella Electric performs commercial load calculations and sizes systems correctly for businesses across the Baltimore area and throughout Maryland, with flat-rate pricing and no overtime charges. If you need your commercial service properly sized, we can help. Financing is available on qualifying projects.