Fusible link in master circuit

Can anyone help me understand why a fusible link would be installed between the main distribution buss and the alternator side of the master switch, even when a circuit breaker is already installed in this same circuit? For the most part Bob Nuckols does a great job of explaining the where's and why's of circuit protection, but this one escapes me. Some of his electrical diagrams (Z11 & Z13) include a fusible link in this circuit but others (Z12) do not. Hoping to understand why and when a fusible link in this circuit should be considered.

Z-12 uses circuit breakers. So the 5 amp alternator field circuit breaker can be installed right on the main bus. Z-11 has fuses. There is no easy way to install a circuit breaker on a fuse block. Therefore the circuit breaker is remote mounted. The wire between the main power bus and the remote mounted circuit breaker needs to be protected from short circuits, thus the fuselink.

Yep! I knew there was probably a common circumstance among systems that utilized the fusible link. Thanks for bringing it to my attention!

Mich48041 said:

Z-12 uses circuit breakers. So the 5 amp alternator field circuit breaker can be installed right on the main bus. Z-11 has fuses. There is no easy way to install a circuit breaker on a fuse block. Therefore the circuit breaker is remote mounted. The wire between the main power bus and the remote mounted circuit breaker needs to be protected from short circuits, thus the fuselink.

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That makes sense; but is there any reason to not use a fuse in the fuse block, rather than the fusible link, to protect the wire to the panel-mounted CB for the alternator field?

Good question. I'm guessing the fusible link can handle higher current for a longer period of time than can a fuse, but I'd like for someone else to weigh in.

Fuses blow much quicker than circuit breakers trip, even if the fuse is a larger value. A circuit breaker is used because it can be reset. A fuse in the circuit defeats that purpose. If you really want to install a fuse, choose a large value, say 30 amps or more.

We are talking about a fusible link, but I believe the reason for it's use is the same as you describe. Slower to open than an actual fuse.