Battery cable sizing and common grounds

[redmexican5081]

I recently decided to rewire my boat.  I got a blue sea systems m-series dual circuit plus battery switch so I can switch the house battery and starting battery on with the same switch.  This switch also gives me the ability to link both batteries together on the off chance I need to jump the starter off the house.  I sized all my wiring for the house side based off the maximum amp draw for my console electronics and came out with a 6AWG cable from the switch to the console.  I also planned on making the lead from the house battery to the switch out of the same 6AWG wire but before I cut the wire to length had the realization that on the chance I ever do use the jump feature or the switch, I need to account for the amp draw to the starter as well.  I have been all through the service manual that came with the motor, 60 HP 1983 Johnson Seahorse, but nowhere in it can I find the amp draw of the starter or even what size wire is recommended. Does anyone know what this starter draws or what size wire I should be using?

Second question, but linked to the first, should both the house and starting battery negative terminals be hooked together and routed to a common ground?  The starting battery right now has a grounding lead attached to the motor. 

[Scott F]

I’m trying to follow your thread but I need you to tell me what a “house” battery is. Also, why would you use a common ground on a boat? Are you grounding each of the electronics and accessories to the hull?

[Tennessee Boy]

If I understand you correctly the wire will be 2 ft at most.  6 gage should be more than enough.  Basically you’re prewiring a jumper cable on a switch.  If you look at jumper cables they run from 10 gage to 4 gage.  The 4 gage ones are usually 20ft long.  

 

 

 

 

[redmexican5081]

22 minutes ago, Scott F said:

I’m trying to follow your thread but I need you to tell me what a “house” battery is. Also, why would you use a common ground on a boat? Are you grounding each of the electronics and accessories to the hull?

House battery is for my electronics, lights, livewells, radio, etc., I planned on powering everything off of a battery that is not connected to the motor.  Currently, everything powered from the dash comes back to the negative  bus bar under the dash and then goes on a 6AWG back to the negative post of the house battery.  When the switch is in "jump" mode the positive terminals would be wired in parallel and I am assuming the negative terminals would need to be as well. Doing this would give the house battery a connection to the grounding wire that connects to the motor block as well.

11 minutes ago, Tennessee Boy said:

If I understand you correctly the wire will be 2 ft at most.  6 gage should be more than enough.  Basically you’re prewiring a jumper cable on a switch.  If you look at jumper cables they run from 10 gage to 4 gage.  The 4 gage ones are usually 20ft long.  

 

 

 

 

Yes this cable would be ~24" long.  This is what I was thinking as well but I know some starters can pull 100+ amps and didn't want to under size the wire.

[gnappi]

A "house" battery (used exclusively for electronics etc.) solves the problem of electronics shutting off when the Engine starts, or the TM gets bogged down in weeds or mud. 

 

Also, since electronics use so little current, the house battery can be used to start the engine should the starting battery go dead. 

 

 

 

 

 

 

 

 

 

[WRB]

The reason high end bass boats use a house battery today is the big engines run on a computer that requires full 12v to operate and start up. Running today's larger size multiple sonar units and livewell aeration systems draw down voltage to the point the big engine doesn't start at the end if a days use 

TM batteries should always be seperate from engine cranking battery.

Tom