RCD, ELCI GFI between ABYC and ISO codes

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

  1. klims106
    Joined: Jul 2011
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    klims106 Junior Member

    I am now confused.
    We are working on a 50 ft steel trawler having grounding issues. The boat need to be compatible with worldwide electric systems. Equipment boat side is 230V/50Hz.
    We are in the process to decide to add a galvanic isolator. According to the ABYC(2009, I do not have the 2012 E section), we need to have the RCD on the Shore side of the galvanic isolator...
    According to the ISO/IEC code(60092-507), the RCD should be on the Boat side of the Galvanic isolator. The ISO also mandate that the Shore power land side has an RCD thus putting the responsibility on the marina....
    It seems the ISO code makes more sense but assumes that all marinas around the world will follow the same code. The boat side RCD detects the fault on the boat, the RCD on land protects both the shore power cable and the galvanic isolator.
    The ABYC seems to make little sense mostly in the case of a Steel boat. The RCD in the input side of the galvanic isolator only and soly protects the galvanic isolator. If a leakage current (not a true ground fault) happens on the secondary it will loop through the ground pont on , the primary side will never see the current differential. If the shore power cord has an issue and is leaking because it is in the water the RCD will not see it either as the leakage current will travel back to the source. The only leakage current the RCD will detect is a transformer internal fault.... What am I missing?
     
  2. michael pierzga
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    michael pierzga Senior Member

    Are you fitting a shorepower induction, isolation transformer on this metal boat ?

    Is this boat multi phase or single phase ?
     
  3. klims106
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    klims106 Junior Member

    Yes the this is a shore power galvanic isolation transformer. Boat side AC is is 230V/50Hz single phase.
    In normal condition shore power only feeds a bank of battery chargers. They feed a large battery bank (24V/2000Ah). A 15 kW bank of inverters feed the boat systems...
    When at sea we also have a Gen 25kW set capable to feed the chargers to maintain the 24V loads and the boat AC load directly.

    As a backup, shore power can also feed the boat directly thru a set of interlocked breakers to avoid paralleling. All was OK while the boat was in the Med.
    Here in the US because of the split phase at the dock, we have issues with grounding.
    Note: Most of the appliances are not sensitive to the frequency difference. A few cannot be turned ON when connected directly to the Shore power.

    So we are going to install an isolation transformer per ABYC to go from Split phase 240 to single phase 240V... Thus the discussion which side of the isolation transformer do we need to install the RCD...
     
  4. CDK
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    CDK retired engineer

    You've assessed the situation correctly.
    An RCD on the primary side of the transformer cannot see any imbalance on the secondary circuit, so it does not protect against shocks or even electrocution. It would only trip for a current leakage within the transformer, a task better left for the land side RCD because that can also see cable damage.

    From the transformer secondary, one terminal must be wired to ship's ground to ensure proper phase and neutral throughout the circuits. The RDC comes directly behind the ground point.
     
  5. klims106
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    klims106 Junior Member

    Thanks CDK. Then why does ABYC want it to be on the primary side? How do I tell the suveyor that I cannot follow ABYC required practice because it is not doing anything sensical?
     
  6. CDK
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    CDK retired engineer

    You could install one RCD on the primary to satisfy the silly ABYC requirements and a second one on the secondary to provide protection.

    This shows once again that what is printed isn't always true (bible and Koran are other examples).

    The use of a real transformer to obtain isolation is very rare because it is expensive, most boat owners use a diode device thinking they have complete isolation. Maybe the guy who wrote the book at ABYC had that in mind. Or his necktie was too tight!
     
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  7. powerabout
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    powerabout Senior Member

    Currently the US regulations are out of step with the rest of the world, they know it and are working on it.
    Bonding earthing is another issue that needs an update
     
  8. botanybay
    Joined: Jun 2011
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    Location: Redondo Beach, USA

    botanybay Junior Member

    Similar question, RCD's, Isolation Transformers, Chargers

    Thank you all for an interesting read trying to solve a similar problem on my 55' sailboat.

    Vessel is wired for 230V 50hz English power. I am trying to work through to a "clean" solution which will work most anywhere in the world.

    One option is to convert incoming power to 24V DC and then use an 8kva inverter to make the correct power form. This limits the "unique" problems to the AC power feeding the chargers.

    Being that the current "primary" marina has significant voltage on the ground which causes everyone to burn up zinc (I replace the MaxProp Zinc every 2 - 3 months) I would prefer to be completely isolated with respect to ship and shore ground.

    I would also like to be able to use a very broad input voltage battery charger to provide the DC power.

    So, if the ONLY items connected to shore power are the battery chargers is there value in the large isolation transformer assuming I am using an RCD at the shore power inlet?

    If power is any of:
    115V 60hz (hot, neutral, ground)
    208V 60hz (hot, hot, ground, neutral not used)
    240V 60hz (hot, hot, ground, neutral not used)
    230V 50hz (hot, neutral, ground)

    The shore power system would look like:

    inlet -> RCD/50A Circuit Breaker -> 30A Circuit Breaker -> 100A Charger (3kw)

    There might need to be two of the chargers but I think that the average loads and the size of the battery bank will make the 2800W of power available from the charger enough that the battery will not cycle very much.

    The question is if there is an RCD (Residual Current Device) switching two poles at the inlet and don't use USA neutral. Do I need to bond shore power ground to ships ground? i.e. is the battery charger and RCD effectively doing the same thing as the isolation transfomer?

    Thank you for any insights.

    David
     
  9. CDK
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    CDK retired engineer

    The simple and effective solution is to cut the ground wire from shore power immediately where it enters your boat and connect the boat's side to DC ground. In the same location install an RDC with 30 mA or lower tripping current.

    The RDC compares current running to and from the boat; if these are not equal the device cuts the power. That's all you need as long as the available shore power is within your suitable range and the 50 vs 60 Hz difference causes no problems.

    To be able to cope with ANY situation, use a switching charger that accepts 100-250V and run the whole system from your inverter.
     
  10. jonr
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    jonr Senior Member

    I agree with CDK. But be aware that on a non-metal boat, you can still have problems with one part of the boat having a voltage difference from other parts and then the water completes the circuit (which destroys parts). No shore power needed.
     
  11. botanybay
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    botanybay Junior Member

    Making all power with inverters and chargers.

    Yes, that is the plan, the only thing connected to shore power would be the battery chargers (for example the mastervolt 100A 24V charger which can handle anything from 90V to 265V and 45hz to 65hz).

    Then use two inverters, one to supply the 50hz circuits and a second to supply the 60hz circuits.

    Note that nowhere will these two systems share a panel. The only common connection would be that as neutral is bonded to ships ground when inverting they share a common ground and thus a common neutral.

    The tricky question is when wiring the RCD at the shore power inlet. Ideally I will not be dependent on having a neutral (i.e. two hots of a 240 split phase) and thus what do I connect the neutral pigtail on the RCD to?

    I am not sure if this pigtail is used to power the circuit or just used as a method of tripping the breaker by running a small amount of current around the measuring toroid to induce the trip for test purposes.

    Since shore power should always have a ground in the shore power cable, one option would be to connect the neutral pigtail to shore power ground.

    Another option would be to connect the neutral pigtail to ships ground. In either case if the only purpose of the neutral pigtail is to induce a fault for test purposes this should work but would it meet "code" for either ABYC or CE?

    Thanks again!
     
  12. CDK
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    CDK retired engineer

    The ground contact (often called PE or protective earth) is connected to the metal part of the RCD itself and is not connected to any circuit. I would tie it to ground wire from the shore power cable.

    The test function uses a resistor across the device (diagonally) to simulate imbalance.
     
  13. botanybay
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    botanybay Junior Member

    Thank you very much! One more question of RCD breakers

    I have been researching breakers and concepts and have two options:

    1) Use a two pole RCD breaker (combined 50A breaker and RCD) and use a custom shore power cable for each of the configurations.

    2) Use a three pole RCD breaker wired to a 50A 240V US shore power inlet. Then after the RCD use a double pole switch to be able to select one of the following:

    L1 - N --> for 120US
    L2 - N --> for 120US
    L1 - L2 --> for 240VUS / 208US / 230V European

    This would allow me to hook up to a US style marina and select which line I wanted to be on.

    On the other hand there is significant complication (the extra switch) and the cost of the three pole RCD is quite high (~$500 USD) vs the more common two pole units which are in the $200 USD regime.
     
  14. CDK
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    CDK retired engineer

    If it is just to power the switch mode chargers, the configuration is irrelevant, so you don't need a 3-phase RCD or a selector switch.

    But you may need one or more short adapter cables to cope with various marina sockets.
     

  15. botanybay
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    botanybay Junior Member

    RCDs from Blue Sea

    The engineer at Blue Sea states that their ELCI (RCD) devices are frequency and voltage sensitive. I have a call into north shore to determine if the same issue exists for their devices.

    I am noticing that some devices out there are specifically 50/60 hz and some are 50hz or 60hz only. Probably the absolute calibration at the other frequency or the broadband nature of the components used.

    Now the harder question is if there is a single device which can work from 100V to 250V to match up to an international battery charger.

    Then, as you say, just run two wires and a ground to the point of the ELCI, drop the ground at that point, connect AC ground for the battery charger to ships ground.

    Any fault in the charger which would go to ground will trip the ELCI and everyone is happy.

    The question would be does dropping the ground at the ELCI and hooking AC ground to ships ground (not neutral to ground!) meet ABYC and CE requirements?

    Thanks!
     
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