Branch Circuits, Feeders, and Service Calculations
Branch Circuit Basics
Know the branch-circuit classifications (general purpose, multiwire, individual, appliance) and the rules for receptacle spacing, GFCI/AFCI protection, and required circuits in dwellings. A common trap is confusing which rooms require GFCI versus AFCI, or applying dwelling rules to commercial occupancies.
Load Calculations
Service and feeder calculations follow standard methods: general lighting (3 VA/ft² for dwellings), small-appliance and laundry circuits, appliance demand factors, and the optional versus standard method. The optional method often produces a smaller service and is a favorite exam topic. Range, dryer, and HVAC loads use specific demand tables-do not simply add nameplate values.
Demand Factors and the Largest Motor
Apply demand factors exactly as tabulated. Remember to add 25% to the largest motor load when computing a feeder or service. A frequent trap is forgetting the 25% adder or applying it to every motor.
Worked Example
Dwelling general lighting: 2,000 ft² × 3 VA/ft² = 6,000 VA. Add 1,500 VA per small-appliance circuit (two minimum) and 1,500 VA laundry. Apply the dwelling demand factors from the table to the total. If an answer omits the laundry circuit, it is wrong.
Exam Strategy
Write the load components in a column, apply each demand factor separately, then sum. Most errors come from applying a factor to the wrong component.