Wiring aluminum boat

Discussion in 'OnBoard Electronics & Controls' started by fishNduck, May 27, 2007.

  1. FMS
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    FMS Senior Member

    Is the ground wire at the gas dock only for metal boats?
  2. CDK
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    CDK retired engineer

    I don't think so. It is a matter of local regulations; in some northern countries it is not required at all. Around the Mediterranean sea it is mandatory: they always clamp a ground wire to the sea rail before filling.
  3. Ike
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    Ike Senior Member

    You think so: This is what happens to an ungrounded tank being filled.

    Granted this is not a boat, but it is exactly the same principle, and I have investigated boat fires where this occurred. That is why the regulations in the US and Canada, and all countries that follow the RCD and ISO, require the tank to be grounded and metal fill fittings be grounded to the tank. All countries with fire codes require that the nozzles and hoses and pumps at gas stations be grounded as well. This is why they tell you make sure the pump nozzle is in contact with the fill before you start pumping gas. That way everything is grounded and any static buildup will just go to ground.

    It is a fact that static will build up on a hose (the fill hose) when fuel is gushing through it. Experiments have also confirmed this. That is why the fill has to be grounded and the fill needs to be connected to the tank ground.

    This is a well established safety issue.

    Whether to isolate the dc system from the hull of a metal boat or not is an issue of corrosion. Stray current corrosion. Those of us who believe you should isolate the system from the hull do so because, why provide an easy path for stray currents to enter the water? The whole point of prevention of stray current corrosion is to prevent any current from getting to the water.

    Yes, sometimes people do inadvertently connect grounds to the hull when they are wiring in new equipment. But that doesn't make it a good thing to do.
  4. Quatsino Boater
    Joined: Feb 2011
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    Quatsino Boater Junior Member

    Hi hope this helps

    2010 EDITION
    APRIL 2010
    TP 1332E

    8.3.1 All switches and controls shall be marked to indicate their usage except where there is a switch or
    electrical control whose function is obvious and where the operation of the device could not, under
    normal operation, cause a hazardous condition.
    8.3.2 Single-pole breakers shall be installed in the positive conductor.
    8.3.3 Switches shall be rated for the voltage and the current rating of the connected load of the circuit.
    8.3.4 The marking on electrical equipment, such as ignition systems, motors, pumps, fans, and controllers,
    shall include the following:
    (a) manufacturer;
    (b) product ID, serial number, type, model;
    87 of 150
    (c) voltage, amperage, wattage;
    (d) polarity; and
    (e) ignition protected, if applicable;
    8.3.5 Circuit breakers shall:
    (a) have the same DC voltage rating as the system voltage;
    (b) be of the trip-free, manual reset type; and
    (c) have an interrupting capacity to meet the system requirements.
    8.3.6 Fuses shall be:
    (a) of the same nominal voltage as the system voltage; and
    (b) of an interrupting capacity to meet system requirements.
    8.3.7 Every integral overcurrent protect device without manual reset is permitted for use provided the circuit
    is protected by a fuse or trip-free breaker.
    8.3.8 All permanently installed electrical equipment and appliances shall be securely mounted to the ship's
    8.3.9 With the exception of engine mounted equipment, all DC appliances and fixed electrical equipment
    shall be designed so that all current carrying parts are insulated from exposed electrically conductive
    8.3.10 The following devices need not comply with paragraph 8.3.9 if one conductor is connected to the
    exposed electrically conductive parts, provided that the connected conductor is the negative conductor,
    the polarity of both the negative and positive connections are identified, the device is mounted only on
    a non-conductive surface, and the device is not bonded:
    (a) communication and audio equipment;
    (b) electronic equipment;
    (c) instruments and instrument clusters;
    (d) cigarette lighters;
    (e) liquid level gauge transmitters; and
    (f) navigation lights operating at 12 V or less.
    8.3.11 Every exposed conductive non-current part of electrical equipment that may normally be in contact
    with bilge or seawater shall be connected to a DC grounding system, except for small vessels not
    equipped with a DC grounding system, double insulated devices, and isolated metal parts in nonconductive
    8.3.12 Grounder liquid level gauge transmitters mounted on metallic fuel tanks or tank plates shall have the
    transmitter negative return conductor connected directly to the engine negative terminal or its bus. This
    conductor shall serve as the tank bonding or static ground conductor. Where this conductor is
    employed as the grounding conductor, it shall be not less than 8 AWG, and no other device shall be
    connected to the conductor.
    8.3.13 The negative terminal of the battery and the negative side of the DC distribution system shall be
    connected to the engine negative terminal or its bus. The negative return on vessels with outboard
    88 of 150
    motors shall be connected to the battery negative terminal unless provisions have been specifically
    provided for the return to be connected to the motor negative terminal by the outboard manufacturer.
    8.3.14 Where an accessory negative bus is used, the following requirements apply:
    (a) all the connections of the accessories to the bus shall be branch circuits from the same
    (b) the negative bus, the negative return conductors, terminals, and connections shall have an
    ampacity equal to the panelboard feeder; and
    (c) the negative return conductors from the panelboard feeding the branch circuits, using the
    accessory bus, shall be the same size as the positive feeder to the panelboard.
    8.3.15 Where the DC distribution system is a two-wire system with supply and return, the engine block may
    be used as the common return for accessories mounted on the engine, except on metallic vessels where
    the engine is not isolated from the hull.
    8.3.16 If a small vessel with a grounded DC system has a multiple engine installation with grounded cranking
    motors that includes an auxiliary generator engine(s), the engines shall be connected to each other by a
    common conductor that can carry the starting current of each of the grounded cranking motor circuits.
    Multiple outboard motors shall be connected at the negative battery terminal.
    8.3.17 If a small vessel is equipped with a crossover (parallel) cranking motor system in a multiple engine
    installation, including auxiliary generator(s), the engine shall be connected with a cable large enough
    to carry the cranking motor circuit; this cable shall be in addition to and independent of any other
    electrical connections to the engines including those in paragraph 8.3.16, except in the case of
    ungrounded DC systems or outboard motors.
    8.3.18 If a paralleling switch is installed in crossover circuitry as described in subsection 8.3.17, it shall be
    rated to carry the largest cranking motor current. The switch may be of a maintained type or solenoid

    8.5 Grounding
    8.5.1 Where a small vessel has more than one gasoline engine, the grounded cranking motor circuits shall
    meet the requirements of 8.3.16.
    8.5.2 The engine block may be used as the common return for accessories mounted on the engine, except on
    metallic small vessels, where the engine is not isolated from the hull.
    8.5.3 A metallic hull or the grounding conductor shall not be used as the return conductor. If one side of the DC system is to be grounded, the grounded conductor shall be of negative polarity. In steel and aluminum small vessels, non-conducting exposed metal parts of electrical equipment that
    requires grounding shall be effectively grounded to the hull.
    8.5.4 On small wood, fibre-reinforced plastic and composite vessels, a continuous grounding conductor shall
    be installed to facilitate the grounding of non-conducting exposed metal parts of electrical, electronic,
    and communication equipment that requires grounding. The grounding conductor shall terminate at a
    point on the main engine or at a copper plate of area not less than 0.2 m2 fixed to the keel below the
    light waterline so as to be fully immersed under all conditions of heel or trim.
    8.5.5 Every grounding conductor shall be of copper or other corrosion-resistant material and shall be
    securely installed and protected, where necessary, against damage and electrolytic corrosion.
    8.5.6 Every grounding connection to the small vessel's structure, or on wood, fibre-reinforced plastic, and
    composite small vessels, to the continuous grounding conductor, shall be made in an accessible
    position and shall be secured by a screw or connector of brass or other corrosion-resistant material
    used solely for that purpose.
  5. pistnbroke
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    pistnbroke I try

    ye gods..may the lord help us
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    BATAAN Senior Member

    Was working in a boatyard near the water on an old shipyard site and kept getting shocked, only at certain times, by the big 42" ship saw with the power off. Went to the power pole, put a meter on the copper ground rod connected to the green wire system and stuck the other end in the damp earth and got 70 volts potential!
    Some muffinbrain had cut off a 3 phase hot cable on the pier and at high tide it was under water and nicely hotted up the safety ground system of the whole shipyard, then stopped when the water went down so was untraceable. I don't like to think of what was happening to the half dozen or so nice boats that were close.
    1 person likes this.
  7. Ike
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    Ike Senior Member

    Yes. whoever did that was ignorant or just plain stupid. But let's be careful here not to confuse AC and DC.

    AC on a boat is a whole different ball game and has to be done in strict adherence to the rules. If you get a ground fault with AC you are talking about shock hazard that kills, both on the boat (someone touches the metal hull) or in the water.

    As for the question;
    The answer is no, it is for all boats. There is one exception to grounding the fuel fill to the tank and boats system. If the boat is a trailerable boat, and you do your fueling at auto gas stations, AND, the boat has a solely plastic fuel fill, the fill should not be connected to ground. The USCG put out a bulletin on this several years ago. Below is an e-mail I received from the USCG.

  8. CDK
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    CDK retired engineer

    Thank you for that post BATAAN.
    I have repeatedly warned on this forum not to trust the shore ground unless you have the means and understanding to establish that it really is what it should be.
  9. CDK
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    CDK retired engineer

    ""You think so: This is what happens to an ungrounded tank being filled.

    Thanks for the video Ike. It looked more or less convincing but the reporter spoiled it all by saying that you should switch off your cell phone to avoid static buildup.

    I cannot judge what really happened there, but the situation is hardly comparable with the tank in a boat. On a dry dusty road vehicles build up a considerable static charge (well over 5000 Volts), enough to make your hairs stand up when you stick an arm out and get shocked when you pull a parking ticket. I don't see that happen in a boat.

    But of course the tank and anything belonging to it must be grounded. Your boat is the best ground electrode there is and all it takes is a piece of wire.
  10. Ike
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    Ike Senior Member

    CDK, as is too often the case, the media people knew only enough to make them dangerous. When this happened I checked it out. The Air Force has a great accident investigation program and the reports are available to other military services. It;s simple. the guy was filling a plastic portable gas can, and did not take it out of the truck bed and set it on the ground. The truck also had a plastic bed liner compounding the problem.When he started fueling he did not make adequate contact of the fuel nozzle with the container and it flashed. The video says the rest. That is why all gas stations have signs warning about fueling portable containers.

    The same applies to a fiberglass (plastic) boat sitting on a trailer, insulated from the trailer by rubber rollers or beds covered with carpet. You can get a flash if you do not make definite contact between the nozzle and the fill, before pumping. It has happened and Imanna Labs did the study to find out why. What resulted was that you actually shouldn't have a ground wire for plastic fills. This does not include plastic fills that are chromed or have a metallic coating. The point is to ground the nozzle to the fill before pumping, which is what you do with your car when filling up. The nozzle is grounded through the ground wire in the fuel hose, to the ground in the pump. SO any static charge should drain to ground.
  11. Mat-C
    Joined: May 2007
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    Mat-C Senior Member

    So... just to be sure that I truly uinderstand, I did this little drawing at work.... do I have it right?

    Attached Files:

    • dc.jpg
      File size:
      524.9 KB
  12. CDK
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    CDK retired engineer

    99% OK Mat-C.
    Just add an anchor light switch for the 360 deg. white light and a diode to power it from the running light switch as well.
  13. michael pierzga
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    michael pierzga Senior Member

    Remember that your boats electrical system must be completely " floating" .

    Negative must not be allowed to touch the hull. Naturally you must choose all isolated, two pole marine equipment, alternators, engine sensors.... and use best practise when installing.

    After you have wired up all gear and the hull is proven free of electrical contact, the best way to keep it that way is to use two pole, positive and negative breakers... or positive and negative knife fuses, at the main dc electrical distribution box. Trouble shooting and isolating an earth fault in a system without a two pole breakers is troublesome.
    Control switches....bilge pump on or whatever function are typically located in a second box and are single pole switches
  14. BertKu
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    BertKu Senior Member

    Could you explain why? I cannot see that anybody can allow to have the floating electrical system to build up static. After some friction, somebody touch the laptop and most likely goodbay laptop. If you state, have a 100 Ohm resistor or 1 KOhm resistor from the electrical systems to the alluminium hull, I could possible agree with you. But floating, I unfortunately put a question mark at your statement.

  15. BertKu
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    BertKu Senior Member

    Please explain 8.5.4 (#34 CONSTRUCTION STANDARDS FOR

    versus your proposal of "floating".

    In all regulations in the world I have read: the grounding of the common negative to the hull, at some point, that it always make contact with the seawater. Is this different in Spain?
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