Big Fat Ground Wire

Discussion in 'OnBoard Electronics & Controls' started by papabravo, May 27, 2013.

  1. papabravo
    Joined: Sep 2012
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    Location: Northern Virginia

    papabravo Junior Member

    Sorry about the subject line.. best words I could come up with.

    I Googling and came across this quote:
    Sounded pretty good to me. Is this a sensible idea?

    Original source:
  2. Mark Cat
    Joined: Jun 2011
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    Location: Michigan

    Mark Cat Senior Member

    It really depends on the type of DC loads and the distance from the power source.

    With one large return there is a common ground impedance. A large current device will modulate across this impedance.

    In general, my approach is to minimize or eliminate any common ground impedance.

    In using boat cable from the source to load you can minimize the current loop area (improve cancellation).

    Sheathed boat cable can be easily separated on a per circuit type basis to reduce crosstalk between systems.

    Also, there is a lot of well known techniques (brackets, hangers, cable trays, ladders and clamps) in running sheathed DC boat cable without resorting to conduit for individual conductor protection.

    Per the boat requirements, bundling of DC reds may impose a conductor bundling derate.

    All for now,

    Mark Cat
    1 person likes this.
  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Using common ground terminals is a sensible way to wire 12V items like instruments and and lights. Engine instruments are usually powered from a single cable already (Mercruiser).

    High current loads like an anchor winch, inverter or fridge usually deserve their own wiring straight from the battery bank. The most important part of planning is calculating the maximum power drain and estimating the cable length, then select a ground wire that will have less than 2% voltage drop.
  4. papabravo
    Joined: Sep 2012
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    Location: Northern Virginia

    papabravo Junior Member

    OK. Got it.

    Seems like I'd use the common ground for essentially the cabin lighting, and the occassional 12 volt receptacle.

    Not on a common ground: windlass, reefer, inverter, engine instruments (they are not on the house bank any way).

  5. T0x1c
    Joined: May 2013
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    Location: Luxembourg

    T0x1c Junior Member

    I guess you speak about the negative (black) circuit. If the engine is not bipolar wired, then your DC circuit will probably be grounded through the engine block/shaft.
    The only other grounding should be for the metallic case of the inverter via a hull grounding plate, in case of default on the inverter.

    Edit: inverter should be on the house bank. Windlass should be as well if you want to keep engine battery totally separated -unless you have a specific windlass battery, but then battery management becomes really complicated.
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