2nd Battery Wiring - Circuit Breaker Location

[oakley24]

I have seen this done both ways, hoping for some guidance. Which setup below is correct? Inline circuit breaker (heading to the helm with a 12 panel fuse block) before +bus and 6 panel fuse block or circuit breaker after +bus? I have the 100amp breakers to go to the batteries and a -bus not shown.

 

[FSH 210 Sport]

Put the breaker before the positive bus. That way the bus is protected. How much current is that positive bus rated for?

That’s a 60 A breaker, what size wire are you feeding the bus, the run to the helm and the fuse block with? #10 wire is good for 30A continuous, #8 is good for 55A continuous.

You need to make sure that the wire running to the helm from the engine compartment cannot be overloaded by the 60A breaker and melt/catch on fire. If say you are going to run #10 to the helm from the positive bus, then you need a 30A ckt breaker on the line side of your positive bus to the helm to protect that wire run up to the helm.

The same could be said for the wire running from the positive bus to the fuse block if that wire is less than #10, otherwise the wire going to the fuse block becomes a fuse. Does that make sense? Once the wire is connected to the bus within your fuse block the fuses within that block in turn protect the wires leaving the fuse block from overloading and or the device that the wires are feeding.

How much load do you think you are going to have at the helm and on the fuse block?

 

[oakley24]

The positive bus is rated 150 amp max. I have #4 from the batteries to the helm as well as the fuse block by the batteries. I'm not sure exactly what I'm going to add, but a fish finder, audio upgrade, LED lights, inflatables pump for sure. I know it's over engineered for a 19' boat, but I guess that's better than under engineered.

And, thanks for the explanation on the fuse or circuit breaker matching the wire size. That always seems to be a confusion point for many, me included.

 

[FSH 210 Sport]

Dang dude! #4? That’s good for 110A’s! One of my favorite sayings is “overkill is underrated“. You won’t have any issues with voltage drop!

Just be careful with a wire size that large that you coordinate your protection, breakers or fuses, correctly. You can always over protect something, just have to be careful that the breaker will not be “blind” to something that doesn‘t have the capacity to carry the capacity of the wire / breaker, which it seems like you do. You can always just put an ATC in line fuse holder to protect the wire to the fuse block if needed.

You can think of fuse / breaker protection as a series of overlapping zones from the smallest at the device end fault magnitude to the largest which in this case is the battery .. where each zone is backed up by the next largest zone