Planning on running 8 gauge marine wire up to a blue sea fuse box in starboard rod locker, then a couple Garmin 106 and a live scope black box off of that fuse box. Do I need a negative bus? Are there any pros/cons to using an on/off switch versus a circuit breaker in the battery compartment to turn everything on and off while I'm already back there turning on the TM and cranking battery connection? Thanks!

1 minute ago, wonkyrig said:

Do I need a negative bus?

If you're running a fuse box, the negative buss is built in.

 

2 minutes ago, wonkyrig said:

Are there any pros/cons to using an on/off switch versus a circuit breaker in the battery compartment to turn everything on and off while I'm already back there turning on the TM and cranking battery connection?

I use the circuit breakers mounted close to the batteries as my on/off switches for main power. Electronics (sonar, lights, aux power, etc) are each on their own switch after the fuse box.

Generally speaking, using circuit breakers as disconnect switches is not recommended. Switches are designed for repeated use and circuit breakers are not. Cycling circuit breakers too often can result in premature failure. 

Late to the discussion, but it depends which Blue Sea fuse block was purchased.  They make a variety, some with and some without negative bus.  Some have common positive bus others have independent circuits without a positive nor negative bus.  I only know this because I was researching them and looking into if I wanted to use a fuse block in my kayak setup.

 

Which fuse block did you purchase?

So this is how I have my boat wired.  Same thing blue seas fuse panel  with 8guage wire. Now before the fuse panel I have a battery switch back in the back as that fuse panel is dedicated to my electronics only. Pumps, ignition, running lights all run off the acc switch and key switch(for ignition) also on a perko style battery switch. Also need to look at putting a 100-120amp fuse with a reset on the positive before the switch just incase. Then I ran 12guage to my units (2 93sv up front, a HDS 12 touch and a 106ulta at the console) and black box. 14 guage to data hub and rod locker lights. If you're doing all this  add a switch or use a rocker switch to turn your black box on and off when not in use.  Hope all that helps. It's nice when all your electronic fuses are in one spot and easily accessible. 

Went with 6 gauge, a blue sea breaker/switch, and a blue sea 6 circuit fuse box. Now to do some tidying and get the graphs mounted and connected to it. Thanks gents.

Do not wire the TM into that fuse box unless the box is rated to at least 60 amps. Split the TM and 'house' wiring at the circuit breaker.

TM is on its own breaker/switch up the other gunwale. This for chartplotters only and the specs check out with blue sea's charts and circuit calculator, plus headroom.