RCD, ELCI GFI between ABYC and ISO codes

Discussion in 'OnBoard Electronics & Controls' started by klims106, Jan 17, 2013.

  1. CDK
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    CDK retired engineer

    My source of information is a recent Siemens product catalog in Dutch language.
    There are devices for 120/240V grid voltages, 240/400V and 500V. The most versatile series is 5SM3, including models for 50-400 Hz and one low voltage type for 24-125V.

    Your question about ABYC/CE requirements I cannot answer.
     
  2. Landlubber
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    Landlubber Senior Member

    ABYC is trying to protect PEOPLE, we try to protect the boat...unfortunately the ABYC system is arse about to look after the boats.
    They are well aware of this, and I know from a few years back, have been looking at ways to protect both, but I think they are still trying. Nigel Calder has written a few excellent articles on these subjects, but there appears to be no simple answer.
    The two types of universal earth leakage systems work differently too of course.
    ELCB (ELCI) Earth Leakage Circuit Breaker (Interuptor) and RCD (Residual Current Device).
    The first type detects stray currents from active to the earth (ground), the second actually measures the supply and return thru the unit and switches off if there is an imbalance, so in fact they are two different devices, just getting confused by people thinking they do the same thing.
    Understandable cos the end result is the power suitches off if there is a leak...it is just achieved differently.
    RCD on the inlet line, 240-240 isolation transformer and RCD on the output of the transformer seem to me to do the best job.
    Also incorporate a Galvanic Isolator with Capacitor. The capacitator allow AC to pass whilst blocking DC
     
  3. taniwha
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    taniwha Senior Member

    wrong ISO standard

    The correct ISO standard for electrical systems on board small craft is ISO 13297 for AC and 10133 for DC.
     
  4. jonr
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    jonr Senior Member

    I'm not following this. Once you have an isolation transformer, is there any need to connect your boat to shore ground at all?
     
  5. Ike
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    Ike Senior Member

    Jonr; depends on how the transformer is wired. If by shore ground you mean the green grounding wire, then maybe, yes, maybe no. Some have the shore green wire connected directly to the green on the boat. Others have the green on shore end at the case of the transformer (primary side). On the boat (secondary side) the green is connected to the white neutral and has no physical connection to the green on the primary (shore). In the first case you need a galvanic isolator in the green grounding wire on the boat. In the second you do not because the transformer is the source of power. No DC can inadvertently flow through the green to shore.
     
  6. jonr
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    jonr Senior Member

    > Some have the shore green wire connected directly to the green on the boat.

    I suggest that this be avoided.
     
  7. Ike
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    Ike Senior Member

    I agree.
     
  8. Landlubber
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    Landlubber Senior Member

    There are still a few problems to be solved. The ABYC states that the Isolation Transformer needs to be grounded, this is done on the chassis of the Isolation transformer (the primary windings are of course, not connected here)
    ABYC also states that the boat ground be connected to the boat neutral, and also to the boats central grounding point, now this then creates a link to the sea again, so the need for the galvanic isolator.......without the grounding to the sea, yes, the galvanic isolator would not be required......now for the 120 and 240 story, you will have to get someone in the USA to comment please, as I live in Australia, and our system here is different to yours (AC that is), so it would be best for me to not comment in case I am misleading.
     
  9. jonr
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    jonr Senior Member

    > now this then creates a link to the sea again, so the need for the galvanic isolator....

    On which wire?
     
  10. Landlubber
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    Landlubber Senior Member

    The green earth wire..........(in Australia at least)...not so sure with the yanky system.
     
  11. jonr
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    jonr Senior Member

    Which one? Ie, when you have an isolation transformer and no ground connection between the boat and shore, why do you need a galvanic isolator and exactly where would it be in the boat's circuit? What low level voltage path are you blocking?
     
  12. Landlubber
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    Landlubber Senior Member

    There is risk of electrification within the boat still mate, just because you have protected the boat, if there is a fault to earth within the boat then the boat still needs to be grounded, it is this grounding wire that I am talking about. The Galvanic Isolator is in series with this wire to the earth plate, or point on the boat.
     
  13. jonr
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    jonr Senior Member

    Galvanic isolators don't protect anyone from electrocution. It might prevent some low level leakage current flow in a metal hull, but that would be gone as soon as some grounded appliance touched the hull. I conclude that a galvanic isolator inside a boat already isolated by a transformer is unnecessary (unless some code requires it).
     
  14. Landlubber
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    Landlubber Senior Member

    Galvanic isolators don't protect anyone from electrocution....course not, but the green wire it connectes to certainly can mate.
     

  15. Ike
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    Ike Senior Member

    Lets get back to basics. The green grounding wire is not supposed to have any current in it. It used to be called the "safety wire" because it simply provides an alternate current path back to ground at the source of power in the case that there is a ground fault, that is a hot wire touching something it shouldn't. like the metal case on an appliance. If there were no green wire then the current would attempt to flow through you to ground (earth, literally). So with a green grounding wire connected to earth ground at the source of power the current flows back to ground without shocking you or someone else. But remember this is AC current.

    Where the problem on a boat arises is that there is a common ground for AC and DC. (and very good reasons for it so don't think I'll just not use the common ground). If there is a fault in the DC circuit you can get DC leakage current in the green wire, which can result in stray current corrosion. This leakage current is usually very low amperage and is not a shock hazard, but can cause your underwater fittings to corrode rapidly.

    So hod you you stop DC current flow in the green wire. That's what the galvanic isolator does. It is just four diodes in what is called a bridge that allows AC to flow (should there be an AC ground fault) but does not allow DC to flow, thus stopping stray current corrosion.

    In effect you are cutting the green wire for DC, but not for AC.

    Now, If your green wire does not go back to shore, that is it only goes as far as the secondary of the transformer, which is now considered the source of power, then you don't need a galvanic isolator.

    here's a diagram of how this is wired
    [​IMG]

    Also see here: The connection between AC, DC, Bonding, Grounding, and Lightning Protection systems. http://newboatbuilders.com/pages/electricity14.html
     
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