AC wiring

Discussion in 'OnBoard Electronics & Controls' started by bcervelo, Jul 9, 2012.

  1. bcervelo
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    bcervelo Junior Member

    I have been asked to do some work on a boat when i looked at the wiring diagrams I came across this schematic of the AC wiring.
    Am i right in saying that connection between neutral and earth should not be there? Would the GFI trip?

    Attached Files:

  2. Bglad
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    Bglad Senior Member

    I will take a stab at this one. The earth and neutral connection for the dock power will be at its source on shore so should not be made aboard as shown in the diagram. The earth and neutral should be connected at the generator which will only be made when it is used as the power source. This is according to ABYC in the USA but I think it works the same in the UK.
  3. gonzo
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    gonzo Senior Member

    That connection should not be made for safety reasons. If there is a fault to earth/ground it will electrify the water and metal parts of the boat. That is always a problem with generators.
  4. MechaNik
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    MechaNik Senior Member

    That drawing looks correct enough. I would include an earth leakage detector in the link by means of a CT.
    Whilst there are two schools on this topic to simply now not make that connection is incorrect.
  5. BertKu
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    BertKu Senior Member

    I quite like the idea, that the LED indicates that somebody has not folowed the rules and swapped the neutral with the hot wire. That red LED must not be on and then , yes , then one could consider to make that connection, otherwise you have a nice short circuit.

    I believe that one should use an isolation transformer between the boat and shore. In that case the connection shall be done. Provided the earth on the isolation transformer is only to shore and not connected to the boat. The boat should be earthed to the water. But I suspect that there are different views on this issue.
  6. philSweet
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    philSweet Senior Member

    So add a momentary "press to test" switch to the jumper. And remember to push it.
    The reverse polarity indicator will not work without it.
  7. mydauphin
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    mydauphin Senior Member

    Also check all the grounded appliances you buy, specially Chinese, they are hard grounding to neutral. Isolation transformers are great if you can afford weight, and space.
  8. Ike
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    Ike Senior Member

    As presented in that diagram I would not make that connection. That connection does not polarize the system. Correctly wiring the system, correctly wiring the shore power plug and the inlet plug, establishes the polarity of the system.

    When AC is brought aboard without a transformer, just a direct connection, the neutral (blue in the diagram) and the grounding wire (green) are not connected on the boat, because they are connected back at the source.

    There are exceptions: If a transformer is used then they are connected at the transformer, because the transformer is the source of power.

    If there is a generator on board, when the system is shifted using a transfer switch, the generator becomes the source of power. The neutral and grounding wire are connected internally inside the generator, but outside the generator they are not connected.

    The same is true if the power source is an inverter. The neutral and grounding wire are connected internally inside the inverter, but outside the inverter they are not connected.

    The neutral and grounding wire should only be connected at the source of power, whether that source is ashore or on the boat.

    This is true of most appliances, not just Chinese. Most household AC appliances have the grounding wire (green) and neutral (white) wire connected. That connection should be broke if the appliance is used on a boat.

    A polarity indicator is good. Reverse polarity can result in serious shock hazards.
  9. BertKu
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    BertKu Senior Member

    MMMh, that would mean, if somebody has swapped the life (hot) with the neutral on shore power and you would press the proposed "test switch", you will blow the the galvanic isolator. Not a good idee. Before you make that connection, you switch the system on and check whether the red LED via the galvanic isolator is on or off. If off, then one can connect the jumper. The galvanic isolator is part of the unit.
  10. CDK
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    CDK retired engineer

    Any low resistance path between AC wiring and (protective) ground is a mistake, both in the USA, the UK and anywhere else in the world. The generator is floating, so it tends to put equal power on the live and neutral terminals. I wouldn't mind that, but if it bothers someone, connect neutral to ground through a resistor/capacitor pair so no damage can occur. The grounding point must not be just anywhere to the nearest yellow/green wire, but to a reliable object like a grounding plate or the propulsion unit.
  11. BertKu
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    BertKu Senior Member

    Hi CDK, could you just clarify the above. Do you mean on the boat it is a mistake to connect neutral AC wire to ground?. I personal feel, only if you use an isolation transformer.
    On the shore the generator is a 3 phase star system (Probably a nuclear PowerStation and the voltage is transformed down from > 220KV down (or higher) to 380 V AC star, of which between R, S, T phases and ground you have 230 V AC. The same applies in the USA, but they only work with a lower Voltage of 110 V AC.
    I cannot see, why one should not connect the neutral wire to ground, if the generator is the big Nuclear power plant on shore. Alright you may trip your leakage current switch, should there be one. This will only trip if the neutral is earthed far away from your position your boat is. Should you be far away from an earthed star position, you may have a dangerous potential voltage difference between neutral and earth/ground.
    I personal don’t like dangerous voltage potential on the neutral and would earth/ground it after checking with the red LED, whether some jerk has not swapped the neutral and life somewhere in a plug on shore. If the red LED is off, I would earth/ground it.
    I agree with you, if it is a floating stand alone 220 V AC generator, the rules are different.
  12. Lt. Kludge
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    Lt. Kludge Junior Member

    It creates a ground loop, which causes electrical noise to circulate around the loop between the PE/N connection at the transformer and your boat. More importantly in your marina it can make your grounded thruhulls slightly off voltage from actual ground which will give you galvanic corrosion problems.
  13. philSweet
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    philSweet Senior Member

    um, yeah, that could happen too. Depends on the bits and pieces. Somebody took the trouble to write that note on the schematic, though. I'm not familiar with the PN call out for the isolator.
  14. BertKu
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    BertKu Senior Member

    You see, I would ground it at the point on shore, before it comes onto the boat (if no isolation transformer is used, which I prefer). Then the question is, is that still unwise.

    Like you said, the imbalance between the 3 phases creates a current in the neutral centre point of the star transformer's formation. The centre point in the star formation is always earthed to avoid static creeping up. But that centre point in a harbour maybe 5 miles away and then I fully agree, you will have earth stray currents between neutral and ground/earth.

    Some countries has the star centre point grounded every so many meter, or ground it via the armoured metal in underground cables. Other countries does not allow to have 230 V mixed with Industrial 3 phase use, to avoid to high voltage potential created in the neutral. Holland is one of those countries. South Africa has everything mixed, 230 V use with 3 phase 380 Volt use. One can measure anything up to 30 Volt on the neutral, due to the long distances and having consumer 230 V appliances mixed with 3 phase 380 V industrial equipment.

    Maybe CDK is right and let it float on a boat and take the risk that the neutral is also hot and treat it as life. The corrosion and stray earth currents on a boat is a big problem and more important.

    Maybe I would instead of connection that connection to put a 100 Kilo-Ohm resistor, at least the red LED has a 2nd way to show that we had an jerk, who swapped the neutral with life.

  15. pistnbroke
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    pistnbroke I try

    now you dont seem to have taken into consideration the corrosion caused by linking the hull to would be normal to link neutral to earth via 4 back to back diodes giving a 1.4v drop ...galvanic isolator is the term

    Read up on your canal boat wiring !!!!
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