2.4 Demand Loads, Continuous Loads, and Calculation Setup

Calculation setup before arithmetic

Demand-load questions are usually won or lost before the first multiplication. The master electrician should first decide what is being sized: service load, feeder load, branch-circuit conductor, neutral, overcurrent device, equipment rating, or a plan-check value. A connected load is the sum of loads connected to the system. A demand load is the load after permitted demand factors or calculation methods are applied.

A continuous load is a load expected to run for a long enough duration that code rules commonly require sizing at 125 percent unless the equipment and assembly are listed for 100 percent operation under the applicable conditions.

Do not mix these ideas. Demand factors recognize diversity. Continuous-load adjustment recognizes heating from sustained current. Motor rules recognize starting and operating characteristics. Transformer rules recognize source and secondary protection. Appliance and HVAC nameplate rules recognize tested equipment. A master-level calculation labels each line so the final answer can be defended.

Worksheet format

Use a worksheet even on scratch paper:

1. Identify code edition and jurisdiction or exam reference.
2. Identify occupancy and system voltage.
3. List each load by category: lighting, receptacle, appliance, cooking, HVAC, motor, continuous, noncontinuous, sign, show window, EV, welder, special equipment.
4. Convert all loads to VA or amperes on a common voltage basis.
5. Apply article-specific demand factors where permitted.
6. Add continuous load treatment where required for conductors and overcurrent devices.
7. Add largest motor adjustments where required.
8. Calculate neutral separately when rules allow or require a different value.
9. Select conductor ampacity after adjustment, correction, terminal temperature, and standard-size device rules are considered.
10. Check equipment ratings, fault current, voltage drop, and plan notes.

This structure prevents a common exam mistake: answering the wrong question. If the stem asks for calculated load, stop at calculated load. If it asks for minimum conductor ampacity, continue through continuous load and applicable adjustment or correction. If it asks for overcurrent protection, apply the device selection rule. The same project data can produce different correct numbers depending on the target.

Demand factor and continuous-load comparison

Example setup

Assume a non-dwelling feeder supplies 42,000 VA of noncontinuous load and 18,000 VA of continuous load at 208 volts, three-phase, and no other demand factors apply. If the question asks for calculated feeder load for sizing conductors under the common continuous-load rule, set it up as 42,000 + 1.25 x 18,000 = 64,500 VA. Convert to current: 64,500 / (1.732 x 208) = about 179 amps. The final conductor and overcurrent selection would then require ampacity table use, terminal temperature review, conductor material, adjustment and correction, and standard device selection.

If the same problem asked only for connected load, the answer would be 60,000 VA. If it asked for real power at a given power factor, that would be a different theory question. If it named specific equipment with minimum circuit ampacity and maximum overcurrent protection, nameplate and equipment article rules might replace the generic setup. The exam stem usually tells you which path is intended.

Dwelling and non-dwelling caution

Dwelling service and feeder calculations contain special methods and demand factors that do not automatically apply to commercial, industrial, or institutional buildings. A range, dryer, dwelling appliance, general lighting load, or HVAC selection may be handled differently depending on whether the installation is a one-family dwelling, multifamily dwelling, hotel, dormitory, restaurant, school, office, store, or other occupancy. Do not import a dwelling demand table into a non-dwelling problem because the numbers look familiar.

Likewise, a commercial kitchen is not a dwelling kitchen. A dormitory room is not always a dwelling unit. A house panel in a multifamily building may carry common-area loads that are not calculated as one dwelling. The master electrician should underline the occupancy words before choosing the article or table.

Field supervision and exam traps

In the field, load calculations support permit submittals, service changes, generator sizing, feeder installation, and equipment procurement. The master electrician should verify that the calculation matches the approved plans and actual equipment. If the owner substitutes a larger water heater, adds EV charging, changes HVAC, or adds kitchen equipment, the load calculation may no longer match the installation.

On the exam, traps include applying 125 percent to noncontinuous loads, forgetting to apply it to continuous loads when sizing conductors or devices, using single-phase formulas for three-phase VA, rounding too early, treating spare breaker spaces as load, and using breaker size as load. Another trap is ignoring the phrase all loads are noncontinuous or all loads are continuous. The correct answer follows the stated facts, not a typical job assumption.