Shore power cord?

Discussion in 'OnBoard Electronics & Controls' started by michigangeorge, Dec 27, 2012.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Sure, it is always a good practice to have in AC circuits a CFCI (USA/Canada) or the European earth leakage breaker build in.

    But I rather at a body resistance of 1200 Ohm have a 110 V ac shock, than at 24 Volt. (12 Volt is too low) . At 24 Volt , the heart will cramp and stay cramped, your touch will cramp and you probably will die. At 110 AC, I have a chance, as the heart muzzles will cramp, but you have a fair chance, that you have let go and that your heart muzzles restore. It is just a personal opinion and experience.
    To get back to George in Michigan, does the manual says something about the earth being connected to the secundair minus? I will be very surprised if they did, as the unit looks very professional and well designed. In view that you can have also 110 - 130 V DC apart of 110/60 Hertz , it means , a buck circuit.
    Bert
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    George's device has a plastic case with a 2-wire AC input, so it doesn't need the protective ground from the shore power cord and that is a good thing because shore ground can cause all sorts of trouble, so it should stay on shore. In the plastic box is a switch mode power supply with at least 2500 V isolation between in- and output.

    A GFCI is always a good safety feature.
     
  3. Frosty

    Frosty Previous Member


    Exactly if if the box became fully live you could not get a shock from it. Leave the earth on the dock.

    What ive not made clear here although ive tried to is the earth on the Marina may not be working and or the resistance of a long run to shore down docks that can be a kilometer long is high. It is easier to track down into your neighbours boat, and god help him if he has a connected it to his ground system.

    Ive seen a boat with no prop from this and the prb was his neighbours battery charger.

    I dont use earth. I have a 2 wire system --only.
     
  4. michigangeorge
    Joined: Dec 2003
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    Location: Petoskey,Michigan

    michigangeorge Junior Member

    Thanks again for all the input but you guys have lost me. I'm thinking I'll go back to a conventional Hubble twist-lock setup and lug that heavy cord around. It is way overkill for this little boat but I do like the idea of having a locking, waterproof connection.
     
  5. BertKu
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    Location: South Africa Little Brak River

    BertKu Senior Member

    George, there are people like Frosty who are making you deeply concerned about nothing. Frostry does not understand what really happened. We asked you: Do you have any conductivity between the third earth pin primary side and the minus 12 Volt secondary side. IF YOUR ANSWERS IS NO! than forget about all the rubbish what has made you worried and changed your mind. That product looks an excellent product and the real engineers have made sure it is safe. What Frosty has explained is only possible, if the primaray earth is connected to the secundair side. Only than it could happpen that corrosion takes place. Not because of long distances and resistance between the earth in the transformer building shore power. Even if the manufacturer of this excellent product uses the earth on the primary side, the fact that it is totally encapsulated in plastic and the earth is present does means to me, that they have thought about every possible safety issue. I have many times placed between primary and secundair windings, extra insulation and an earth screen for double safety.That manufacturer may also have done it. Bert

    I have never measured, but most hosepipe water supply, is often a better earth than the offshore power. Does that mean, you are not washing your aluminium or metal boat anymore?
     
  6. jonr
    Joined: Sep 2008
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    Location: Great Lakes

    jonr Senior Member

    As I recall, the summary regarding running a ground from the dock to the boat is (in no particular order):

    1) use an isolation transformer or,
    2) disconnect/don't use it (but do use a GFCI) or,
    3) use a galvanic isolator

    Pros/cons of each are in other threads.
     
  7. Frosty

    Frosty Previous Member


    And you say Im complicating it. Do you mean the 12v of the batt charger wires--the black???

    So to simplify this, plug in the batt charger and see if any voltage is coming out of the black wire that goes to the batt.

    Is that what you mean?
     
  8. BertKu
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    BertKu Senior Member

    No, as you can still get confused. One measure with a good Ohmmeter and see whether there is any conductivity below 100 K between primary and ANY of the secundair wires, whether it is black, green, blue, red or whatever colour, whether it plus or minus or ground. The only way one can have corrosion acillerated is by having a low resistance connection between the secundair 12 or 24 Volt and any wires of the primary side. No connection ? This brilliant powersupply will not course any corrosion. That extra black secundair wire is maybe there for the 2 x 5 Ampere or for a secundair ground, totally isolated from primary. Those people are not beginners, one can see that they made something good and waterproof.
     
  9. BertKu
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    BertKu Senior Member

    The thread starter did buy a unit and asked for advise. The above is only appicable when you start from scratch, Bert
     
  10. jonr
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    jonr Senior Member

    Buy a plug-in GFCI and cut the ground pin off of it with a hacksaw. With this (plus any extension cord, 2 or 3 wire), you have implemented option number 2.
     
    Last edited: Jan 1, 2013
  11. BertKu
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    BertKu Senior Member

    Yes, mmmmm using a hacksaw. What about he makes a phonecall to the manufacturer and asked the right questions. Is the secundair connected to the primary side via the earth or minus. Yes or No . If No, the manufacturer must have a reason why he still has an earth for the primary side. Bert
     
  12. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Michigangeorge,

    Relax. CDK answered your question some time ago. If Marinco (the manufacturer) provided a two bladed plug, then the device is internally grounded. If there is a three pronged plug then the device is externally grounded and needs to be connected to shore via a standard outdoor waterproof extension cord. Just look at the plug (and the manual, of course).

    Regards, MIA
     
  13. Frosty

    Frosty Previous Member

    Could you explain what internally grounded means.
     
  14. Don H
    Joined: Apr 2012
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    Location: Queensland Australia

    Don H Junior Member

    Hi George, yes it is safe to plug a lead from shore power into this charger. This charger is double insulated with its ABS case and it has the added bonus of being potted internally. This means that live wires are both electrically and mechanically unable to be connected to anything you can touch.
    This unit does have a 3 pin lead and has an earth wire connected to the unit. The reason the manufacturer has taken an earth wire into a double insulated appliance will be for EMC,FCC noise reducion not safety. The charger uses a switchmode rather than a transformer and regulator
    The charger is a 3 stage smart and although the specs do not clearly state it i doubt very much that the negative output will be connected to the earth wire.
    Bert is correct in asking for an ohms reading between the negative output wire and the earth wire. if there is a connection stray currents from other boats could find their way through the grounded parts of your boat, up the charger lead and back to shore earth.Its worth checking but i would not expect a connection to exist. Its not dangerous just not desirable for the metalic parts on your boat as Frosty mentioned.
    A simple multimeter is always handy to have so with the charger disconnected from battery and mains supply measure from the earth pin on the 3 pin lead to the negative charger lead.

    Thanks Don
     

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  15. jonr
    Joined: Sep 2008
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    jonr Senior Member

    Sounds like some people (certainly not me) suggest another option:

    4) run a grounded, 3 wire cord onto the boat and hope that it never gets used in a/another way that connects the dock ground to the boat ground.
     
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