Wiring in accessories

Discussion in 'OnBoard Electronics & Controls' started by Brylk1830, Aug 23, 2008.

  1. Brylk1830
    Joined: Mar 2008
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    Brylk1830 Junior Member

    Hi all,

    Well, I'm starting to think that the act of simply posting on this site- regardless of all the helpful replys I get- helps me solve any problems I may be having :)

    As i've posted before, I have the battery ACR connected so both of my 12 v (starting and accessory/trolling batteries) are being charged independently. Now that that's done I'm ready to start wiring in accessories such as a depth finder, radio, lights, a plug for my trolling motor, and a few 12 volt plugs so I can use a spotlight, keep my cell phone charged, etc.

    Below is a rough wiring diagram of what I have so far with the exception of the hot wire that will supply my fuse panel with it's power. It's a 6 foot run between my battery and my fuse panel and i'm wondering what size wire and fuse I should use to connect to my fuse panel?

    Both of the wires coming from my battery acr are 8 gauge wires with 120 amp fuses. Also, the two negative wires going to my neg bus bar are 8 gauge as well. The only wire that is not 8 gauge is the fused ground coming from my #3 slot on the battery acr and ending at the neg bus bar. Instead, it's a 14 gauge wire fused with a 30 amp fuse.

    Basically, I just want to be sure I will be supplying enough power to my fuse panel in order to wire in the devices i've listed above. Some more items I haven't listed but will eventually be installed are a bilge pump, speedometer, and lighting so I can finally stop buying batteries to power my night fishing trips.

    Lastly, i'm wondering how to install my trolling motor plug socket for example, an item that I assume I will not have to run from the fuse panel? Is the best way to do this to simply wire it into the battery with a fuse? Thanks for any replys!

    Attached Files:

  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The accessories you've mentioned are all light loads that should be connected to the fuse panel, each with an adequate fuse, say twice the rated current for each connected device.
    The ground wire has to carry all the current, so that should be 8 gauge without a fuse. Never install a fuse in the negative leads because if that one blows or gets corroded you may get unpredictable results with different voltage readings all over the system. The negative wire must be totally reliable, it is the reference you need for any voltage measurement in case of fault finding in the future.
  3. Ratch
    Joined: Feb 2008
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    Ratch Junior Member

    For starters fuses (most of the time) are supposed to protect the wiring so if there is a short they blow before the cables catch fire. I think from memory 8 gauge is rated for around 100 amps so 120 amp fuse will not protect anything (you will need to look this up to double check my memory).

    For items that have higher current draw like the trolling motor keep the wires as short and as thick as you can otherwise you waste valuable battery power warming the cables this is an important consideration when dealing with low voltage systems.

    I would keep essential circuits separate for example if your radio wiring or whatever is plugged into the sockets blows the fuses you will still have nav lights if they are on a separate circuit.
  4. murdomack
    Joined: Jun 2007
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    Location: Glasgow

    murdomack New Member


    Good to see you getting it all together. As mentioned above by CDK you will need to check out why you need a fuse in the negative from your ACR, is it recommended by the maker? It doesn't look right, but if they say so. Also, what Ratch says about your fuse ratings between the batteries and the ACR. You might need to change the fuses down to what your cable will carry safely.

    Regarding your trolling motor, if you intend having a plug and socket (I think you guys call it different, receptacle or something) arrangement, you will need an isolator switch between your positive battery terminal and the socket with a fuse before that switch. You will need another cable direct from the negative terminal to the socket as well. Have you already purchased the motor and is there cable with it? I would use heavy cable, like you would run to the starter motor, from both battery terminals to your socket.

    Your negative wiring is not correct in my opinion. You show two wires coming from the common bussbar, one to each battery. If you ever use a jump lead from one battery positive to the other all the starting power will ground through these wires. You should have linked the two battery negative terminals with a heavy cable and used one return from the bussbar. If you install this link you can leave the two grounds from the bussbar as they are as it will give you more ground cable cross sectional area.
    Last edited: Oct 19, 2008
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    FAST FRED Senior Member

    The best way to protect a boat from an electrical fire is BOTH fuses and CB

    The Circuit Breaker is sized to the wire a 15A wire will have a 15A CB, the CB delay in seeing an overload will allow motors to start or other tenp overloads.

    Each device should have a FUSE , rated to ONLY what the device will consume.

    A radio that needs 3 A will make a great fire on a 15A wire set should it die internally. The fuse prevents that.


  6. murdomack
    Joined: Jun 2007
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    murdomack New Member

    That's an excellent safety investment doing it that way, Fast Fred. Good tip.
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