In the PDF linked above on page 3. they compare two different types of radial systems, figures 5-4 and 5-5, and say that:
“A more reliable and maintainable arrangement utilizing multiple primary feeders is shown in figure 5-5. In the
system of figure 5-5, each unit substation is supplied by a dedicated feeder from the service entrance switchgear”
I don’t quite understand why Figure 5-5 is more reliable. Even though the only difference between the two systems is the addition of a switch before the transformer. Would some one care to enlighten me?
I imagine the first switch and fuse would be in the service entrance switchgear and and second switch would be near the transformer. That would facilitate isolation and easier access to the feeder cable and the transformer; this would allow for preventative maintenance to be done without disassembling anything (e.g., disconnecting feeder cable from transformer), but instead just flipping the switches. It’s more reliable because it’s more maintainable.
Above is a snippet.