Master switch question

[db8]

Am going to use Bob's Z-13 diagram, but this question really pertains to any of the diagrams with a master switch. Why is there a fuselink from the Main Power Distribution Bus and a 5 amp CB between between it and the master switch? I thought the fuselink acts like a CB, but in the diagram, it appears to be protected by two means. Would it be ok to just put the 5 amp CB where the fuse link is and call it good? The length of wire from the first point on the MPDBus to the master switch will be 6 inches in my application. Thanks for any thoughts/help on this. Dave

[Brantel]

That is actually the alternator field circuit.

Bob's argument is that the wire feeding the 5 amp breaker may be quite long between the breaker and the fuse block/buss and that this needs to be protected as close as possible to the block/buss.

Alternator field circuit breakers are known to trip often and a 5 amp breaker can be too slow in poping before even a 15 amp fuse will pop.

The fusible link is a very slow blow fuse and helps prevent issues with this.

[db8]

So with post #1 in mind Brian (ie the short run from the buss to the switch), I should be able to just use a 5 amp CB on the MPDBus followed by a 6 inch wire to the switch and be just fine?

[Brantel]

If your CB is right on the buss you do not need the extra fusible link.

[db8]

That's what I thought. Thanks. Dave