Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Marine Electrical Questions

Options
  • 27-08-2019 4:03pm
    #1
    EHP
    Registered Users Posts: 173 ✭✭


    I was asked to do a bit of Electrical work on a fishing boat and just wondering if anyone on here has any experience with this.

    Basically the boat came in from France and was wired in 3 phase 230V ie 110V per phase. The single phase equipment such as lights etc is wired with 2 110V phases as opposed to a 230V and 0V so no neutrals on board. The owner wants to change over to 400V supply. There will be 3 different potential supplies 2 generators 1 will be back up and the shore supply. The generators will not be neutralised and I'm going to be running a neutral from both of them when I change them to 3 phase 400v.

    So my first question is do I need to switch the neutrals or can I join them all in a common connection. If I don't need to switch them the existing change over switching arrangement can stay as is making my job alot easier.


Comments

  • Options
    #2
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    Do the generators have a reference to the boat hull (I’m assuming it is conducive) ? Often in marine applications important equipment (such as navigation equipment) will have no reference to the hull / extraneous metalwork / “earth” so that a single fault scenario will not take it out as this could present a bigger risk. If this is the case it is just as live as the phase so should be switched. Often the integrity of the insulation would be monitored so that the end user would be aware of the “first fault”.


  • Options
    #3
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    Do the generators have a reference to the boat hull (I’m assuming it is conducive) ? Often in marine applications important equipment (such as navigation equipment) will have no reference to the hull / extraneous metalwork / “earth” so that a single fault scenario will not take it out as this could present a bigger risk. If this is the case it is just as live as the phase so should be switched. Often the integrity of the insulation would be monitored so that the end user would be aware of the “first fault”.

    The generators are bonded to the hull and all earthed back to a main earth bar in the main board it's a floating earth using the body of water as the ground essentially or at least that's my understanding of it. Are you saying I have to switch the neutrals from each supply?


  • Options
    #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    EHP wrote: »
    The generators are bonded to the hull and all earthed back to a main earth bar in the main board it's a floating earth using the body of water as the ground essentially or at least that's my understanding of it. Are you saying I have to switch the neutrals from each supply?

    What you have described does not tell me whether the generator has a reference to the earth bar / hull.
    Example: It would have a reference to the earth bar if the star point of the generator was connected to the earth bar.

    Or to put it another way, is it an IT system?
    Are the generators to run in parallel?
    Is there to be a common neutral bar?


  • Options
    #5
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    What you have described does not tell me whether the generator has a reference to the earth bar / hull.
    Example: It would have a reference to the earth bar if the star point of the generator was connected to the earth bar.

    Or to put it another way, is it an IT system?
    If IT then I would switch both poles.

    No the star point isn't going to be connected to the earth so I guess I'll have to switch the neutrals.


  • Options
    #6
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    EHP wrote: »
    No the star point isn't going to be connected to the earth so I guess I'll have to switch the neutrals.

    Well I would, others may disagree. My logic is thy the neutral is at the same potential with respect to the hull as any of the phase conductors as such it should be treated just the same i.e. switched.

    Are the generators to run in parallel?
    Will they load share?
    Will the generators share a neutral?
    Are any of the generators supplying critical loads?


  • Advertisement
  • Options
    #7
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    Well I would, others may disagree. My logic is thy the neutral is at the same potential with respect to the hull as any of the phase conductors as such it should be treated just the same i.e. switched.

    Are the generators to run in parallel?
    Will they load share?
    Will the generators share a neutral?
    Are any of the generators supplying critical loads?

    Generators won't run together just one is back up incase a generator fails at sea.


    Each generator will have a separate neutral back to the main board where they will join in a common neutral bar

    When at sea everything down to the kettle is critical... The main critical load will be refrigeration plant for blast freezing.

    I'm what I would describe as a domestic electrician so a bit out of my comfort zone here but the boat owner is fully aware of my lack of experience in this field, I appreciate any advice given. How are you on changing the supply voltage out of generators that's my next bit of learning as the existing generators are outputting only 3 x 110v phases and no neutral.


  • Options
    #8
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    You need to be very careful. Loss of power at sea can have fatal consequences. As already stated it would be prudent to monitor the integrity of the insulation.

    I did some work in marine environments in the past and had some good notes from an SME. Must see if I can find them.

    In this case the neutral has the same risk as the phase. I would use double pole MCBs or fuses on phase & neutral loads as they are really 2 phase.


  • Options
    #9
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    You need to be very careful. Loss of power at sea can have fatal consequences. As already stated it would be prudent to monitor the integrity of the insulation.

    I did some work in marine environments in the past and had some good notes from an SME. Must see if I can find them.

    In this case the neutral has the same risk as the phase. I would use double pole MCBs or fuses on phase & neutral loads as they are really 2 phase.

    There will be test lights on the panels monitoring for any current in the frame of the boat.

    Why would you need double pole MCBs would the neutral not be at 0volt back to the supply/star point of generator same as any system, of course if you got a broken neutral it would potentially be at 230V again the same as any other system or what am I missing/not understanding.


  • Options
    #10
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    EHP wrote: »
    There will be test lights on the panels monitoring for any current in the frame of the boat.

    That is a bit crude and would only work if the lamp was healthy and the insulation failure was severe. I would go for something more sophisticated that would provide an analog reading so that I could see if the insulation was deteriorating slowly over a period of time.
    Why would you need double pole MCBs

    Just like a 110VAC supply on a building site. One pole is "as live" as thee other.
    would the neutral not be at 0volt back to the supply/star point of generator

    0V with reference to what?
    0V between neutral and earth? Only if you connect the star point to earth and you haven't.

    You have an IT system.

    With an IT system if you were the "neutral" or any of the phases you would be like a "bird on a wire" and would not get a shock once there is no other connection to earth (or in your case the hull).

    On another note, consider high IP ratings for all enclosures, devices etc. that do not corrode and are UV resistant.


  • Options
    #11
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    That is a bit crude and would only work if the lamp was healthy and the insulation failure was severe. I would go for something more sophisticated that would provide an analog reading so that I could see if the insulation was deteriorating slowly over a period of time.



    Just like a 110VAC supply on a building site. One pole is "as live" as thee other.



    0V with reference to what?
    0V between neutral and earth? Only if you connect the star point to earth and you haven't.

    You have an IT system.

    With an IT system if you were the "neutral" or any of the phases you would be like a "bird on a wire" and would not get a shock once there is no other connection to earth (or in your case the hull).

    On another note, consider high IP ratings for all enclosures, devices etc. that do not corrode and are UV resistant.

    I taught the star point would be my neutral and each leg would be 240V as such giving me a 3 phase and neutral 400v supply.


  • Advertisement
  • Options
    #12
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    EHP wrote: »
    I taught the star point would be my neutral and each leg would be 240V as such giving me a 3 phase and neutral 400v supply.

    The star is your neutral but it is not at 0 volts to earth if it is not connected to it.


  • Options
    #13
    EHP
    Registered Users Posts: 173 ✭✭EHP


    2011 wrote: »
    The star is your neutral but it is not at 0 volts to earth if it is not connected to it.

    Get what you're saying now thanks for the advice I'll probably be back with more questions as the job goes on. Wire a few lights they said sure it'll be grand FML.


Advertisement