Insulated two conductor systems?

Discussion in 'OnBoard Electronics & Controls' started by iceboater, Oct 9, 2011.

  1. iceboater
    Joined: Jan 2011
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    iceboater Junior Member

    Our maritime authority in Iceland requires all commercial fishing boats to be built to the Nordic Boat Standard.
    In chapter C11 for boats under 15 meters, "ELECTRICAL INSTALLATIONS", it says that "Systems shall normally be installed as insulated two conductor systems"
    There translation of this is that in a fiberglass boat, we have to have twin pole breakers for all loads and all switches have to be twin pole. They require us to use Switches that disconnect plus and minus from all users. I have not found any reason to justify the cost of this. They claim that it is needed to prevent corrosion in the system.
    All panels have to be custom made because we have not found any supplier of DC distribution panels that makes them with dual pole breakers. The breakers are hard to get and supply of twin pole marine switches is limited and expensive.
    I am going to argue against this requirement and I would like to hear from someone that has experience in the field. I am told that in the other nordic countries enforce this standard in a different way.
    Just to give an example of how ridiculous this is, is that to follow their requirements we need to have the float switch for the bilge pump
    connected to dual pole relay that switches the bilge pump on.

    I would appreciate if someone with knowledge of electrical systems in fiberglass boats could comment on this. I need strong arguments against this requirement.

    Does anyone know if this is required anywhere else?

    Or maybe I am wrong?

    Thanks, Axel
     
  2. michael pierzga
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    michael pierzga Senior Member

    I dont know all the reulatory requirements but I have never operated a proffessionally designed and build boat that has a single pole system.

    Other than cost, I cant think of ANY argument against an isolated twin pole electric system.

    The main benefit of a two pole system is controlling stray electricity . Galvanic action effects any metallic equipment. Fire hazard is another issue and obviously the ability to electrically isolate a piece of gear when servicing it is beneficial.

    In your example of a bilge pump circuit, the float switch is normally a single pole device and doesn't need a separate switch, simply a two pole breaker that controls the complete bilge pumping circuit. Down stream of a twin pole breaker may be many single pole control relays or switches
     
  3. Frosty

    Frosty Previous Member

    Are you sure its for Dc as well as AC.

    AC I can understand as both wires can give a shock but your example of a 12V bilge for example is pointless.

    Its never ending regulations . There is a an office some where in the darkened corridoors of government where people get paid to just think stuff up.

    So the battery is pos and neg switched too?
     
  4. iceboater
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    iceboater Junior Member

    Michael, thanks for your reply.
    Is it possible that you are not understanding what I am saying or maybe I was not clear on my description of the system.
    Insulated two conductor system means that you have two conductor from the distribution panel (breaker panel) to
    all users. But the requirement to have the breaker and switch to disconnect both plus and minus pole is what I am arguing against.
    If down stream of a twin pole breaker we could have single pole switches (witch we can not) it would defeat the purpose
    of having dual pole breakers to prevent stray current, wouldnt it?
    How could I put two pole breaker to control the complete bilge pumping circuit when I always need live plus to the float switch.
    The breakers may not be used to switch any users, they are only used to disconnect plus and minus if there is over-current.

    This is what I am arguing against. I can not use single pole switches down current from the breakers
     

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  5. iceboater
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    iceboater Junior Member

    Yes, it is for DC


    Yes, both batteries, start and deep cycle needs to be disconnected with cut off switch on pos and neg. And the deep cycle battery needs to have two pole breaker from the cut off switch to the breaker panel (distribution panel).
     
  6. michael pierzga
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    michael pierzga Senior Member

    I dont know all regulations , Im not a marine electrical engineer., but at this minute Im servicing a DC refrigeration unit on a classed vessel. The power is distributed to the unit thru a twin pole breaker marked "refrigeration" . This two pole breaker feeds DC power to the refer junction box . Inside the junction box is a relay to turn the unit on. This relay is a single pole, breaking the positive side. The control wires to turn this " islotaed" relay are two pole and guarded by two ,plus and minus, fuses. The negative and positive power output from the junction box to the DC motor is additionally protected by 30 amp knife style fuses. The power supply to the cooling sea water pump is twin pole twin fused.


    This is typical of all electric installation I see on isolated systems..

    At present I have hundreds of professionally drawn sheets of electrical diagrams for various vessels isolated electrical installations. . I would suggest to you that you find a guy like me locally, who also has various marine wiring diagrams , then study these wiring diagrams . It will greatly assist you in planning and wire routing
     
  7. iceboater
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    iceboater Junior Member

    Is this vessel steel or fiberglass? How big?


    I am in no short of wiring diagrams and I need no assistant in planing and wire routing.
    I am trying to get professional opinions on why in a fiberglass boat I need to have two pole breakers for pos and neg from all users and two pole switches for all users.
     
  8. michael pierzga
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    michael pierzga Senior Member

    This vessel is 27 meters, aluminium.

    Hull material means little. Size means little. Any piece of marine equipment will be destroyed by the combination of sea water and stray electric current. To have an engine block Negative, single pole, invites corrosion of all the dissimilar metals inside the cooling system and poses a fire hazard if a naked high tension Positive cable contacts the block


    There is a reason for regulations. Are you certain that regulations will affect your vessels. I see many recreational craft with simple single pole electric systems.
     
  9. iceboater
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    iceboater Junior Member

    I just saw that the diagram that I posted does have the engine grounded to the starter battery. I copied it from the Nordic Boat Standard
    and should have put the text with it, as it says,
    "2.2 For propulsion engines with a power less than 100 kW it is permitted that the engine be used as conductor during start,"

    "The figure below shows an example where the engine is used as conductor during start and where either of the batteries can be used to start the engine."

    But in my application the engines are bigger than 100 kw and therefore have insulated alternator and no negative to the engine.

    It is interesting how the professionals that wrote the standard can explain how size matter regarding insulated engine or not.

    From what I have read on marine electricity, hull material is a big factor regarding stray currents problems. Or maybe I need to
    read again.

    I have often found the reason for overregulation is lack of knowledge by those who write them.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Many engines, generators, are temporarily grounded at start. The typical culprit ais the glow plugs. Most ONANS that Ive met are.

    Of course a metal hull is more sensitive to stray current. Paint bubbles off the metal , exposed metal creates a bigger corrosion potential around the boat and everything wears faster. Paint systems are very expensive to repair.

    But every boat is full of dissimilar metals in its systems. A typical water pump failure will be an eroded, pitted, shaft inside the pump that was promoted by stray electricity.

    In the end the only negative feature of a fully isolated DC system is cost. Ask a local marine electrical engineer for cost saving strategies. I see the " ring " system employed on some small home built boats. A pair of high tension DC cables circle or run for and aft the boat. At various points on this ring DC power is tapped off the ring , thru breaker ed junction boxes, to service local equipment. Much less cable in this type of system and since the cable runs are short, less copper content is needed in the cables. Again ask a local guy, perhaps he has clever solutions.
     
  11. goboatingnow
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    goboatingnow Junior Member

    I cannot see in the context of the costs of a 27m vessel. how using double pole breakers has any significant cost effect, They are widely available in Europe ( see Carling). Its the proper way to do electrical disconnects anyway.

    Dave
     
  12. MikeJohns
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    MikeJohns Senior Member

    Not from internal electrical faults.
    The danger with stray external current is from an earth connection to the mains to the bonding system. Then in a marina with an electric field in the water the rates of damage depend on immersed areas. Metal boats will often escape with minor depth surface electrolysis in large patches, wooden and GRP boats scarifice their anodes then their stern gear commonly the damage is worse for non metal boats.
     
  13. MikeJohns
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    MikeJohns Senior Member


    It does seem like overkill, have you looked at regulations for other counties for comparison ? It's certainly no argument to say that it is to reduce corrosion !
     
  14. iceboater
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    iceboater Junior Member

    The nordic countries that use the Nordic Boat Standard are Iceland, Denmark, Sweden, Norway and Finland. DNV, Det Norske Veritas is also using the standard, but they have there standards in much more detail.
    I called the Swedish marine authority, and they are not making this requirement. I have not yet bee able to get hold of the right persons in Norway, Sweden, Denmark and Finland. But I have been told that Iceland and Norway are the only nordic countries that are translating the standard in this way.
    The reason I am posting this here, is to get reply from others who know the regulations in there countries and/ or are willing
    to shear there professional opinion on the subject.
     

  15. powerabout
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    powerabout Senior Member

    In the Dynamic Postioning part of offshore vessels that I work in, the equipment has isolated low side ( like UPS's) so makes it possible to run dual pole breakers but most kit ( unless on the UPS)is not wired that way usually common low side just terminates on a terminal strip ( isolated from vessel) so therefore not all class must require it?
    this does mean 24v kit is all inside its own faraday cage which is earthed to the vessel
    Rare to find small boat kit with isolated earth so pointless as MP points out the glow plugs are a classic and usually the starter.
    Americans dont believe in isolated earth
     
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