One of the most consequential one-line questions is not simply where a conductor starts or ends. It is where the final branch-circuit overcurrent protective device sits. That point separates feeder analysis from branch-circuit analysis.
Technical Basis and Scope
This is NEC Article 100 terminology education based on the owner-supplied NEC 2026 source. It is not a project-specific code determination. Confirm the locally adopted NEC edition, amendments, AHJ interpretation, equipment listing, and actual installation before using it on a permit set or in the field.
Plain-English Control
A feeder consists of conductors between the service equipment, separately derived system source, or other power-supply source and the final branch-circuit overcurrent protective device. A branch circuit consists of conductors between the final overcurrent protective device protecting the circuit and the outlet(s). An OCPD, such as a breaker or fuse, opens a circuit when current exceeds permitted limits.
Field and Permit Impact
In a path such as service to switchboard to panelboard to RTU disconnect to RTU, the final branch-circuit OCPD - not a casual label or conductor location - establishes the boundary. That affects conductor and OCPD selection, panel schedules, load calculations, voltage-drop analysis, grounding/bonding review, and reuse of existing circuits.
Where To Show It
One-lines and risers: source, equipment lineage, OCPDs, and feeder paths. Panel schedules: circuit identifiers and protective devices. Power plans: load and equipment connection points. Existing-condition documentation: traceable panel/circuit origins and unresolved field-verification holds.
Review Path
Start at the load, identify the protective device that is final for that branch circuit, trace upstream to the supplying equipment, and then reconcile names, ratings, conductors, and load data across every document. For an existing building, test rather than infer circuit origin when that fact controls scope or safety.
Do / Do Not
Do identify the final branch-circuit OCPD on every meaningful load path. - Do reconcile equipment and panel designations. - Do not call every conductor leaving a panel a feeder. - Do not classify an existing circuit from an assumed route alone.
Field Tip
When a renovation team says 'this is a feeder,' ask two follow-ups: what is the final branch-circuit OCPD, and what outlet/load does it serve? The answers turn a label into a reviewable electrical path.
Masterbuild QA Lens
A good one-line lets a reviewer trace source, protection, conductor class, disconnect, and load without reverse-engineering the designer's intent. If that chain breaks, the coordination record is incomplete.