Here is a one-line of a distribution feeder. It leaves the substation breaker as a three-phase line, runs down the main road, and along the way two single-phase branches tap off to serve side streets. One of those branches has a fuse where it connects. Off to the right, a switch drawn as an open gap joins this feeder to the next one over. A limb falls on the fused branch. Before reading on, predict it: when that fuse blows, who goes dark, the whole feeder or just part of it?
Just that branch. To see why, learn the three pieces of feeder shape. The backbone is the three-phase trunk leaving the substation, sized to carry the whole feeder’s load. A lateral is a branch, often single-phase, that taps off the backbone to reach customers the trunk does not pass. A tap is simply the connection point where a lateral joins the backbone.
Laterals are fused so a fault on one branch clears by itself. When the limb faults the branch, its fuse melts and opens that branch alone. The backbone and every other lateral stay energized, so only the customers past the blown fuse lose power. That is the whole reason laterals are fused instead of being wired straight into the trunk: a local fault stays local.
A distribution feeder is radial, meaning power normally reaches any point by exactly one path. That makes protection simple but leaves a feeder with no built-in back-up if its source is lost. The fix is the normally-open tie: a switch between two feeders, held open in normal operation. When a section faults and crews isolate it, the operator closes the tie and the neighbor feeder back-feeds the stranded customers while repairs happen. Open in normal operation, closed to restore, never both feeders sourcing the same span at once.
How a utility builds and protects its distribution grid sets the baseline for every equipment order that follows. The Feeder tracks the infrastructure investment and modernization programs reshaping that baseline, free, every week.