Grounding Systems

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Intermediate

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Video/Text

Boat Electrics

4 Lessons

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In the lessons of this brief overview module, we separate out the different components of a grounding system and investigate its core installation requirements. A proper grounding system is vital for the safety of AC and DC systems, corrosion prevention, and lightning protection.

Grounding Systems

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A short introduction to the various grounding circuits we will cover in this overview module.

Video lesson

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In this lesson, we take a look at the common ground point, which we call a grounding bus to distinguish it from what we have called the DC circuit ground. We also learn about the core differences between grounded and isolated ground DC systems.

Video lesson

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We learn about the purpose of all grounding systems plus installation requirements for grounding and bonding systems depending on this purpose.

Video lesson

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Text lesson

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About the teacher

Jan & Nigel

This course has been created in a joint effort by Nigel Calder and Dr. Jan Athenstädt. Nigel is responsible for the lecture notes and Jan will take the role of presenter and guide you through the lessons.

  • There was one question about the combining of grounding wires. In the video, the information given was that all of them can be combined (including AC), but in most cases they are not, but in most cases AC is done separately (because of the 3 core cable). The answer marked as correct states that AC is ALWAYS done separately.

    • Hi Michal,
      Thanks for your comment. I am not sure which part of the video you mean, but I assume it’s the sentence “In theory, its function could be combined with any of the other grounding conductors. But in practice it is always run as a separate conductor, in a common sheath with the hot and neutral current carrying conductors.”?
      I think this sentence might not be as clear as it should have been. While this would work in theory, the standards require that the AC conductor is run in a common sheath. We will clarify this in the next revision of the video.
      Best
      Jan

  • First of all: thank you so much for the course!
    I am a complete novice: high-school physics 45 years ago.

    On my boat the main isolation switch is on the NEGATIVE conductors from the batteries (2001 Bavaria 40 cruiser). This seems unusual. There is no isolation switch on the positive conductors from the batteries.

    If the negative bus-bar was connected to ground then there surely would be a short from positive battery terminals to ground?

    I am wondering if this means that the boat has an isolated DC system rather than a grounded system?

    I would be interested in your thoughts.

    • Murray,

      I believe (but am not certain) Bavaria boats from this era were wired with the battery isolation switch in the negative side of the circuit. In normal circumstances, in a sense it doesn’t matter which side of the circuit the switch is in so long as it truly isolates the batteries. But for decades the ABYC and ISO have settled on negatively-grounded systems having the isolation switch in the positive side of the circuit.

      With your negative side switch, even if the negative side of the boat downstream of the isolation switch is connected to ground it will not create a short circuit to the positive side. For this to happen, there needs to be a short from the positive side to something that is grounded.

      Another installation that is commonly seen (many French-built boats) is a battery isolation switch in both the negative and positive sides.

      There are strongly held opinions in favor of both negative side switching, and switching both conductors. If yours is the original factory installation and not some later owner modification, I would leave it alone. If you want to comply with the current ABYC and ISO standards, I would move it to the positive side, or add a positive side switch.

      Nigel

  • Hi!
    I am trying to solve a grounding issue on my boat.
    it is a cabin cruiser with a rebuilt Penta GL 5.0 and an SX-M outdrive.

    I see many grounding cables being cut in half (f.ex one from fuel intake hose).
    I figured out that one of the battery wires is connected to the engine block, so i started testing with multimeter if i can get a continuity between the grounding screw and anything on the outside.

    It feels like i touched anything that has a chance of being a conductor- and i can’t get my multimeter to beep.
    i touched the propeller shaft, all screws, and i even found steel lines that are “chassis ground” – but still no beep.

    i am stressing now that my boat has no ground, and i possibly put my family at risk when boating.

    but than again – should i be stressed?
    is it enough that the battery is connected to the engine, and i trust that the engine is grounded,
    or is there anything else i should do or test?
    i’m heavily lost

    • Kamil,

      There should not be any conductors on a boat, grounding or otherwise, cut in half without figuring out the implications!! We can’t help you with that. With respect to the grounding conductors, the implications depend on the function of the conductor. Are these, for example, bonding conductors (for galvanic corrosion protection), or lightning protection conductors, or AC grounding conductors? Depending on the function you may have a corrosion problem, or a safety problem, or even, in practice, no problem. The safety issue primarily arises with AC grounding conductors. These are an essential safety feature on our boats to guard against shock hazards in the event of electrical faults. We then have the issue of whether or not there is a connection to the water. If this is a European boat, there may intentionally be no connection to the water from the AC grounding circuits, but in this case, there will be an RCD on the shorepower inlet which you absolutely need to test to ensure that it is functional (it will have a test button). Even if the RCD is functional, the ABYC still requires the connection to the water, as has the ISO since around 2014. In other words, even with a functional RCD it is recommended to have a connection to the water, but if it is not there and you now make it you may create a corrosion issue when plugged into shorepower, especially if you do not have either an isolation transformer or a galvanic isolator. As you can see, this is getting to be complicated! There are a lot of pieces here that have to come together correctly for properly functioning bonding and grounding systems. I think you need to bring in some professional help to make sure you do not end up with a corrosion problem or a potential shock hazard on the boat. I know this will be expensive, but it is important to get these things right.

      Nigel

      • Thank you Nigel for taking time and being so thorough!
        i could not agree more with getting it right.
        Matter is- i have an inner need of doing things on my own, than i know they are done correctly.

        I started working on my own wiring, when i realized that wrong kind of cable is used in my wiring. And every step of the way it gets funnier.
        Cut conductors, no fuses on some loads, wrongly done connections ( crimped, but not shrinked ) – it just goes on and on, to the extent that my wife already tells me we won’t be buying a next boat 🙂

        Given that the boat was repowered and some wiring was redone by professional shipbuilder – i don’t really trust locals 🙂

        that said – my situation is that boat is from US, made in 2001.
        It has an 120VAC shore power inlet, galvanic isolator, however its a 20-year old one, and doesn’t look solid.
        Also I am in Europe, so i would need to convert the installation to 240V, along with all devices on board.

        I was thinking of changing shorepower to 240VAC, but figured out there is so many wiring inside, and so many things to figure out, that it will be simpler to tear everything AC out, and instead i switch to running everything on DC, and adding one inverter to power my kettle / coffee machine, or occasional laptop charger.

        The only other time I’d need AC would be to charge house battery bank – which i was planning to do from shore with victron IP65 smart chargers.

        From what you write, and what i figured out from reading so far, it seems that i won’t need galvanic isolator for that case (if i’m wrong, please do let me know, i do suffer huge uncertainty),
        however i am still very attached to the idea of having a ground connection to water – to connect a VHF, or any other equipment that would require ground.

        That’s my current nemesis – i see a cable from battery going to the engine block, but whenever i try to check for continuity between engine block and anything on the outdrive, it just says “open loop”.
        I had the guy who repowered the engine today look at it, and he said that there are stainless steel wires on the outdrive that are serving as the ground connection. Maybe the issue is that indeed engine block is connected to outdrive with stainless steel. In that case i guess any major current would get to the water, but multimeter won’t be able to test it ?
        so in that case – should i just accept that there has to be connection if i ground the battery to engine ?

        once agin thank you for all your helpful guideance !

        • Kamil,

          The AC wiring on the boat will be sized adequately to switch from 120v shorepower to 230v. You can even use the same shorepower inlet. But you will need to replace all the 120v/60Hz equipment with 230v/50Hz, and likely change the wall outlets to Euro style, etc. In this case, you need a galvanic isolator. If the one you have is not labeled ‘ABYC A-28’ it should probably be replaced.

          The other way to go is to have a single hardwired battery charger as the only device connected to shorepower and to power all the AC devices from a separate inverter (i.e., do not use the pass through mode on the inverter). If the charger has a plastic case, and as such does not have a case ground connected to the boat’s DC ground and the water, you will have galvanic isolation and do not need the galvanic isolator. If the charger has a metal case with a case ground, and this is connected to the boat’s DC ground and the water, you will need the galvanic isolator.

          If your meter is reading ‘OL’ and its internal fuse is not blown, there is no connection between the engine block and the outdrive!

          Nigel

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