Here is a feeder map. A heavy three-phase line leaves the substation breaker and runs down the page; several thinner lines branch off it, and one of those branches ends not at a customer but at an open switch symbol, a small gap in the line. The next feeder over starts at its own substation and runs toward that same gap. The puzzle: this feeder just lost its source. Before reading on, point to the one branch that could pick up these customers from the NEXT feeder. Which branch reaches across to the neighbor, and how can you tell?
The answer is the branch that ends at the open gap, because that gap is a normally-open (N.O.) tie point. To read it, decompose the feeder into four named parts. The main is the three-phase backbone that runs from the substation breaker out into the service area. A lateral is a branch off the main, often single-phase, that serves a street or a rural road. A tap is where a lateral connects to the main, almost always through a fuse cutout so a fault on the lateral blows that fuse instead of tripping the whole feeder. The tie-point is a switch between two feeders, and on a normal map it is drawn as an open gap.
So that open gap is not a mistake on the map. The normally-open tie is the only branch that touches the next feeder, and it stays open on purpose so the two radial feeders never parallel. Radial feeders do not parallel in normal operation; each one runs from its own source. The tie sits open, ready. When this feeder loses its source, an operator closes the tie, and power flows backward from the neighboring feeder to restore these customers.
That is why the diagram earns four different symbols. The thick line is the main and the thin lines are laterals, so you know which one carries the whole feeder and which one serves a single road. The fuse at each tap tells you a lateral fault will clear locally. And the open gap, the N.O. tie, is the spare path: closed only to back-feed and restore, never run closed.
Reading a single-line diagram is the first step to writing a defensible RFQ. DistroForge report editions apply that same fluency to real bid packages: supplier capacity, lead times, and spec language that survives an OEM’s substitution clause.