5.1 Feeder vs. Branch Circuit Boundaries
Key Takeaways
- A branch circuit starts at the final overcurrent device and supplies outlets or equipment loads.
- A feeder supplies a panelboard, switchboard, distribution equipment, or other point where final branch-circuit overcurrent devices are located.
- Service conductors, feeders, and branch circuits use different Article 100 definitions and different sizing rules.
- The exam often hides the boundary by describing panels, disconnects, taps, and equipment rather than naming the circuit type.
Why the boundary matters
A journeyman exam question may say, "A 120/240 V panel supplies lighting, receptacles, and a water heater," and then ask for conductor size, overcurrent protection, or required circuits. Before looking up ampacity, decide whether the conductors in the question are service conductors, feeders, or branch-circuit conductors. NEC Article 100 gives the definitions, and those definitions steer the rest of the book.
A branch circuit is the circuit conductors between the final overcurrent device protecting the circuit and the outlet or outlets. A feeder is all circuit conductors between service equipment or another source and the final branch-circuit overcurrent device. Service conductors are upstream of the service disconnect. Those three terms are not interchangeable on the exam.
Boundary map
| Conductors described | Usual boundary clue | Common NEC articles |
|---|---|---|
| Utility/service point to service disconnect | Service drop, lateral, service conductors, service equipment | 230, 250, 310 |
| Service equipment to panel with breakers | Feeder to panelboard, distribution panel, detached building panel | 215, 220, 225, 240, 250, 310 |
| Panel breaker to receptacle, light, appliance, motor controller, or equipment | Final breaker or fuse ahead of load | 210, 240, 250, 310 plus equipment article |
| Transformer secondary to panel or disconnect | Separately derived system or transformer secondary conductors | 215, 240, 250, 450, 310 |
The word "panel" alone does not prove feeder or branch circuit. A panelboard can be supplied by a feeder, but a breaker in that panel can supply branch circuits. A fused disconnect can be the final overcurrent protective device for a branch circuit, or it can protect feeder conductors to another panel. Trace current from source to load and mark where the final overcurrent device for the load is located.
Code-navigation workflow
- Read the last sentence of the question first and identify what is being sized or selected.
- Circle the load served by the conductors.
- Find the nearest overcurrent device on the source side of that load.
- If that overcurrent device is the final one ahead of the outlets or equipment, apply branch-circuit rules.
- If the conductors supply another distribution point with branch-circuit breakers or fuses, apply feeder rules.
- Use Article 220 for load calculation when the question asks for calculated load, then use Articles 210 or 215 and 310 for conductor rules.
Worked setup: detached garage panel
Suppose a dwelling service panel has a 60 A two-pole breaker feeding a panelboard in a detached garage. The garage panel has breakers for receptacles, lights, and a door opener. The conductors from the house panel to the garage panel are feeders because they run from one overcurrent device to equipment that contains final branch-circuit overcurrent devices. The individual conductors from the garage panel breakers to receptacle outlets are branch circuits.
The exam may ask for the feeder equipment grounding conductor, the number of conductors, or whether a grounding electrode system is required at the detached structure. Those are not Article 210 branch-circuit questions just because receptacles are ultimately supplied. They are feeder and grounding questions, commonly involving Articles 215, 225, and 250.
Worked setup: water heater disconnect
A 30 A two-pole breaker supplies a nonfused disconnect beside an electric water heater. The conductors from the breaker to the disconnect and from the disconnect to the water heater are part of the branch circuit if the breaker is the final overcurrent device protecting that load. The nonfused disconnect provides a means of disconnecting, not branch-circuit overcurrent protection.
If the disconnect were fused and the fuses were sized as the final overcurrent protection for the water heater branch circuit, the conductors on the load side of those fuses would be downstream of the final overcurrent device. The question details decide the classification.
Exam traps
A common trap is treating a feeder breaker as if every conductor leaving it is a branch circuit. A breaker feeding a subpanel is usually feeder overcurrent protection. The final branch-circuit overcurrent devices are in the subpanel, not in the service panel.
Another trap is using branch-circuit receptacle spacing rules for feeders. Required outlet rules in Article 210 apply to branch circuits and outlets, not to the feeder conductor set supplying the panelboard. Feeder questions often care about calculated load, ampacity, neutral load, grounding, voltage drop recommendations, outside feeder rules, and conductor protection.
A third trap is confusing an outlet with a receptacle. An outlet is a point on the wiring system where current is taken to supply utilization equipment. A receptacle is one kind of outlet. A lighting outlet, smoke alarm outlet, range outlet, or hardwired equipment outlet can still be a branch-circuit endpoint.
Quick classification drill
| Scenario | Classification |
|---|---|
| Conductors from a 20 A breaker to bedroom receptacles | Branch circuit |
| Conductors from service disconnect to a lighting panel | Feeder |
| Conductors from meter to service disconnect | Service conductors |
| Conductors from a panel breaker to a fused rooftop unit disconnect | Usually branch circuit to equipment, unless the disconnect feeds other branch devices |
| Conductors from a 100 A breaker to a tenant panelboard | Feeder |
For R17, T17, and G17 exams, expect the same logic even when the exact edition changes a table number, dwelling rule detail, or GFCI/AFCI scope. Start with definitions, then follow the conductors. The NEC is organized around what the conductors are doing, not around the installer shorthand used in the field.
A 100 A breaker in service equipment supplies a panelboard with multiple 15 A and 20 A breakers. What are the conductors from the 100 A breaker to that panelboard?
Which step should usually come first in a feeder versus branch-circuit exam problem?
A nonfused disconnect is installed beside a water heater supplied by a 30 A breaker. What is the usual classification of the conductors from the breaker to the water heater circuit?