Branch Circuits, Feeders, and Service Equipment
Branch circuit design
Know the branch circuit types and their ratings, the rules for receptacle and lighting outlets, and how continuous versus noncontinuous loads are treated. Understand that continuous loads are calculated at 125 percent for conductor and overcurrent sizing, and that specific appliances and motor circuits have their own articles. Be able to compute the minimum number of small-appliance and laundry circuits and explain demand factors for dwelling units.
Feeders and services
Understand feeder and service conductor sizing, the role of calculated load, and how demand factors reduce the calculated load without reducing safety. Know service equipment components: service drop or lateral, service entrance conductors, service disconnect, service panelboard, and grounding electrode system. Recognize the difference between the service point and the service disconnect location.
Traps in questions
Watch for applying a demand factor where none is permitted, forgetting the 125 percent continuous-load multiplier, confusing feeder and branch circuit overcurrent rules, and assuming the service disconnect must be outside. Another trap: treating a calculated load as the actual connected load.
Worked example
A dwelling has a 12 kW electric range. Rather than sizing conductors to the nameplate, apply the Code demand allowance for household cooking equipment, then size the branch circuit and overcurrent device from the resulting load. Rule of thumb: calculate, apply permitted demand, then size; never size from nameplate alone.
Practice approach
Practice full dwelling load calculations end to end, tracking each step on paper so you can find your own arithmetic slips.