Electrical Load: Connected vs Demand

An electrical load calculation estimates how much power a service, feeder, panel, or other distribution equipment may need to supply. It organizes lighting, receptacles, appliances, heating, cooling, motors, and other equipment into a load schedule. The result is not simply the sum of every nameplate in every situation because some loads are unlikely to operate at full output simultaneously.

A useful calculation separates the connected load from the expected or preliminary demand load. Connected load shows the total of the inputs entered. Demand load applies a stated method for diversity or noncoincident equipment. Keeping the two values visible makes the assumptions easier to review and prevents a demand estimate from being mistaken for a complete code calculation.

Connected load is the total rated load included in the schedule. It is useful for understanding the equipment installed and for identifying large contributors. Demand load is a planning estimate of the load expected to occur at the same time after applicable demand factors or noncoincident rules are considered. The correct method depends on the project, jurisdiction, equipment, occupancy, and applicable code section.

For example, heating and cooling equipment may be treated as noncoincident in a preliminary dwelling model when both systems are not expected to operate at their maximum at the same time. That assumption is not universal. Equipment controls, local climate, heat-pump operation, supplemental heat, and the adopted code method can change the result.

A continuous load is commonly discussed as a load expected to operate for three hours or more, but the applicable code definition and calculation section control. In many conductor and overcurrent calculations, continuous load is treated at 125 percent while noncontinuous load is treated at 100 percent. That does not mean every input in a service calculation should be multiplied by 1.25 automatically.

The StructoCalc model exposes an Other Continuous Loads input and applies a 125 percent adder to that separate value so the assumption remains visible. It does not determine whether a real appliance, motor, HVAC system, or occupancy qualifies under the adopted code. Verify the correct treatment for the project and avoid applying the same factor twice.

Begin with floor area and the general-load assumptions required by the chosen method. Add small-appliance and laundry circuits when the method calls for them. Record the nameplate wattage of the water heater, range or oven, dryer, dishwasher or disposal, electric heating, cooling, and other equipment. Do not replace missing nameplate data with a guess when the actual product information is available.

Next, select the system voltage and phase so the calculator can convert watts to an estimated current. Review connected load, preliminary demand load, the larger heating or cooling input, and the continuous-load adder separately. Then compare the schedule with the panel, feeder, service, generator, or transformer being considered. If the project has motors, EV charging, solar, storage, commercial equipment, or a three-phase system, use the appropriate specialized method and professional review.

Service sizing is affected by the adopted code, local amendments, equipment ratings, motor and HVAC rules, demand factors, conductor ampacity, voltage drop, phase balance, grounding and bonding, utility requirements, and inspection requirements. A preliminary calculator cannot verify all of those conditions from a few inputs.

Use the Electrical Load Calculator to organize a transparent first estimate and identify the loads that need review. Have the final service, feeder, panel, breaker, generator, transformer, and conductor design completed or reviewed by a qualified electrical professional. Never work on energized equipment.