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  1. #1
    Join Date
    Jan 2008
    Posts
    43

    Default Galvanic Isolator Installation Position

    Hi,

    Nigrl Calder has the following diagram in his book:



    (Sorry its not a great picture!).

    I am a bit surprised that he is so adamant that position 2 is the only "correct" place for the GI.

    Since:
    A. If the GI is working either position is fine.
    B. If the GI fails closed ie conducting freely galvanic protection is lost in both cases
    C. If the GI fails open ie no conduction at all then in position 1 (the "wrong" position) we loose the earthing of the DC negative/bonding system (bad) but in position 2 (the "correct" postion) we loose all earthing of AC and DC.

    Am I missing something here? Are any of the above assumptions (A - C) wrong?

    Cheers
    martin

  2. #2
    Join Date
    Nov 2003
    Posts
    25,721

    Default

    No, in Pos 1 you still have the capacity to make a circuit. In Pos 2 you are covered from the boat point of entry into the circuit.

    Why would you do anything else?

  3. #3
    Join Date
    Jan 2008
    Posts
    43

    Default

    Hi FC,

    Are you saying that in position 1 you might be able to accidently bypass the GI in installing a new bit of kit for example?

    cheers
    m.

  4. #4
    VicS is offline Registered User
    Location : Home: Kent. Boat: Chichester
    Join Date
    Jul 2002
    Posts
    31,806

    Default

    The possibility of installing a GI in position 1 was something I raised for discussion a few weeks ago.

    See http://www.ybw.com/forums/showthread.php?t=216556

    The only objection was in connection with metal boats, but I am not 100% certain about that.

    In a later discussion on galvanic isolators Halcyon recalled that when they first came in they were in fact fitted between the incoming earth and the DC grounding point etc. ie position 1

    See his second contribution to http://www.ybw.com/forums/showthread.php?t=216403 post number 39 in the thread.

    The safest option, especially with metal boats perhaps, is to use a pontoon mounted isolation transformer both from the point of view of galvanic isolation and personal safety.
    Sea Wych Owners Association: www.Seawych.org

  5. #5
    Join Date
    Nov 2003
    Posts
    25,721

    Default

    Quote Originally Posted by svaha View Post
    Hi FC,

    Are you saying that in position 1 you might be able to accidently bypass the GI in installing a new bit of kit for example?

    cheers
    m.
    Well, obviously that possible, either by you, or the next owner of your boat if he doesn't know that you haven't followed the recommendations.

    I just put mine as close to the shore power input plug as possible - that just makes sense, doesn't it?

  6. #6
    Join Date
    Jan 2008
    Posts
    43

    Default

    Quote Originally Posted by VicS View Post
    The possibility of installing a GI in position 1 was something I raised for discussion a few weeks ago. ....safety.

    Many thanks for pointing me to this previous discussion, I guess this answers my question really...it prefectly reasonable to put the GI in either position and position 1 has some advantages it could be argued.

    As to why I am considering position 1 at all, its just that on my boat installation at position 2 would be a great deal of effort, position 1 is 30 mins work...

    thanks to all repliers
    cheers
    m.

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