You are correct. The "final branch-circuit overcurrent device" is the last overcurrent protection device (fuse or circuit breaker) before the load (utilization equipment) that it protects.Now, regarding a building supplied by a branch circuit, you are right to question that, as it's not common, but does exist. Here's the breakdown: Feeders vs. Branch Circuits

A feeder supplies power from a source (service equipment, generator, etc.) to a subpanel or other distribution point. A branch circuit extends from the final overcurrent protective device protecting the circuit to the outlet(s) supplying the load.

When a Building Might Be Supplied by a Branch Circuit

This typically occurs in small, detached structures that have a very minimal load. Examples include:

A detached garage with only a few lights and receptacles

If the garage is wired with a single circuit (e.g., a 20-amp circuit from the main panel) and that circuit goes directly to the garage without any intermediate panels, then it's considered a branch circuit supplying the building.

A small shed or outbuilding with a single light

Similar to the garage example, if only minimal power is needed, a single branch circuit might suffice.*

Irrigation controllers, low-voltage landscape lighting transformers

These might be fed from a branch circuit extending from the main panel.The NEC allows for a building to be supplied by a branch circuit, it must comply with specific requirements (e.g., overcurrent protection, grounding, and bonding).So, while less common than a feeder, supplying a building with a branch circuit is permissible when the load is very small and meets all applicable code requirements. It's essentially a way to provide power to a small, detached structure without the need for a subpanel.

In the context of 250.94(A)(4)(b), which deals with grounding electrode conductors, the distinction between a feeder and a branch circuit supplying a building is important for determining the appropriate size and type of grounding conductor. Flag for review