Common Ground Wiring Question

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cutch9138

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Parker Nation,

I'm in the process of moving batteries, and straightening up my random wire situation. Here is my question..

I have two ground buses in the cabin, there are two 8 gauge ground wires that leave the cabin and go to the negative post on one battery.

The engine ground also goes directly to the negative post on one of the same battery.

The ground bus in the transom has a 10 gauge wire going directly to a ground post on the same battery.

The two batteries are connected via a jumper.

My thoughts.

Connect all grounds from the cabin and the engine to bus in the transom. Use an 8 gauge ground wire from the transom to one of the batteries.

Do I need to worry about overloading the bus in the transom? It is the stock bus put in at factory.

the pics below are of the ground bus in the transom, and current battery setup.
 
I guess it helps if I post the pics.
 

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Cody, I'm in the middle of some of this now myself. My thoughts.. if you connect your engine ground to the bilge bus, then you will need to run about a 2AWG from the bus up to the start battery. This is because that is about the size of the AWG from the engine? I'm looking forward to someone else answering the 2nd part because I think that the cold cranking amps for the engine are somewhere around 600? I don't think that the bus in the bilge can handle that? Even if you upgrade that bus, I'm not sure if setting it up tha way would be the way to go? The harness from the engine has one lug (neg) going to the start battery neg and the other lug (pos) is going to your battery switch. This is why I say it would need to at least be of equal size of the engine ground if not one size larger?
 
Shawnee, that' a good point about the 2 AWG leaving the bus, I didn't think about that. Blue sea systems has a 2 bank system diagram that has a 150 amp common ground amp post for the engine and both batteries. I don't see what would be the difference would be other than the bus ratings. Even if I end up having to connect engine ground directly to the battery I wouldn't mind. I really want to hook up the cabin ground buses to the bilge bus, but i'm not sure if that is ok?
 
That sounds logical to me. I've been doing some research along with asking questions here on CP about this stuff also. I'm in the process of adding a battery charger and very soon afterwards an inverter. Both in the transom area and both needing case grounds that I want to run to the bilge bus. So this has caused me to go down this similar road on the neg bus. I just removed my bilge bus yesterday to clean it and also to remove and redo the 10 gauge ground that went from it to my start battery and replace it with a 2AWG. Ironically I was searching Blue Sea Sys site earlier and I was checking to see if I should just put a heavier capacity one back in its place. Your post was good timing for me as well. There are a few guys on here that are pretty knowledgeable about this stuff so I'm going to hold of my bus order now until I see what you learn here.
 
I think that the cold cranking amps for the engine are somewhere around 600?

I have a 400amp DC Amprobe just for measuring Starter cranking amps.

The highest I've found so far was about 275amps on 225 Merc Opti.

Every motor other than that was a bunch less. The starter cranking amps spec, you will not find in any book. Not a factory manual either. Believe me I've looked. This is why I have that amprobe.

Automotive manuals have this spec for cars.

The simple way on your question is. Upgrade to a higher amp Buss bar for the transom.

Use something like the Blue Seas pt # 2116 or 2126

13176383.jpg






Now were talking the Neg side only here.

Start Battery Eng GND and 4ga or 2ga GND that goes to the House Battery

House Battery then has a 4ga cable going to that GND Buss.

All other GND's go to the GND Buss.

That way you have only 2 connections on each NEG Battery terminal.

Be sure to caot the whole Buss Bar with dialectric grease after connections are made.
 
Thanks as always for clearing this up Wart! I think I'm going to go with the 2128 for the 6 smaller #10 post for the few 12/14G wires down their I need to connect also and I still have 2 5/16 studs for 4 of those. The principle is what you are suggesting which is 250A capable. My inverter case ground requires the same size line as the supply side and that will have a 250A fuse on it. The guys at Xantrex tech confirmed this type of bus with 2/0 AWG from case to bus and bus to start battery was the way to go. If I ever need to ground anything else to it in the future it will certainly handle it. Thanks.
 

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Thanks guys for your sound advice, I really appreciate all of your help. After I replace the scuppers (if they ever come in, been 3 weeks) I'll be able to finish up getting the wiring squared away. Then, I'll show the end result. Thanks again
 
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