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One black and two red electrical switches

Discussion in 'Ask A Beneteau Owner' started by Bluenose, May 22, 2018. Add this thread to a FAQ

  1. Bluenose

    Bluenose

    Joined Jan 10, 2018
    91 posts, 15 likes
    C&C & Beneteau 331
    Ca Halifax
    Hi folks, just getting used to me new to me B331. One red is for house, the other marked starting.......what is the "Negative Common" black switch for?
     


  2. Davidasailor26

    Davidasailor26

    Joined May 17, 2004
    1,508 posts, 350 likes
    Beneteau Oceanis 37 LE
    US Havre de Grace
    Assuming it's still in the factory configuration that switch is a cutoff for all the ground lines before they go back to the battery. Some owners re-wire that to re-purpose the switch as an emergency cross-over between the batteries.
     


  3. Bluenose

    Bluenose

    Joined Jan 10, 2018
    91 posts, 15 likes
    C&C & Beneteau 331
    Ca Halifax
    So what would be the use for it?
     


  4. Davidasailor26

    Davidasailor26

    Joined May 17, 2004
    1,508 posts, 350 likes
    Beneteau Oceanis 37 LE
    US Havre de Grace
    You mean the use for it in the factory configuration? It's pretty useless. In theory it's a quick way to cut off all power to all circuits, but the red switches can do that basically just as well. I've never seen a great explanation on its purpose. There's been some other discussion about it here in the past. Check out for example https://forums.sailboatowners.com/index.php?threads/battery-ground-switch.168123/ and https://forums.sailboatowners.com/index.php?threads/battery-switches.132698/
     


  5. Gunni

    Gunni

    Joined Mar 16, 2010
    5,765 posts, 1,397 likes
    Beneteau 411 Oceanis
    US Annapolis
    The Black is the 12vdc negative lockout. When you have a deep kimchee electrical situation you snap off the red positive switch and then the Black negative, in that exact order. The concept is that you take your batteries out of the fuss. Eliminates any unknown parasitic 12vdc loads if you are wired accordingly, but many DIY guys wire to ground around the switch, so you have to know your system.
     


  6. Stu Jackson

    Stu Jackson

    Joined Feb 26, 2004
    20,258 posts, 780 likes
    Catalina 34
    224 CA Maple Bay, BC, Canada


  7. Ron20324

    Ron20324

    Joined Jan 22, 2008
    6,707 posts, 798 likes
    Beneteau 323
    US Annapolis MD
    Nothing wrong with the switch system. The best reason I have heard for the ground switch is to prevent someone in the cockpit hitting the start button while someone is working on the engine. Me, I replaced & rewired that black swich with a red one to accomodate a third battery. Great system!
     


  8. Maine Sail

    Maine Sail Moderator

    Joined Feb 6, 1998
    10,824 posts, 633 likes
    Canadian Sailcraft 36T
    US Casco Bay, ME

    If your vessel is wired like many Bene's you don't likely have "HOUSE" and "START" you simply have two battery banks that are in parallel when both switches are set to ON. Leave both switches set to ON, and discharge too far, and you're dead in the water. I have a number of Bene & Jenneau customers who've learned this the hard way..

    Unfortunately many, but not all Beneteau's, have a bussed switch system where by HOUSE and START switches are permanently bussed together on the load side of the switches. Any time both red switches are turned ON both battery banks are in parallel. Many owners are unaware of this wiring scenario and incorrectly assume they have "isolated" HOUSE & START banks.. If your boat has this wiring it is best to correct this issue.

    Below is what this wiring looks like. The issues are listed on the drawing, if your boat has this wiring scenario. Link to full size image if needed: http://www.pbase.com/mainecruising/i...1/original.jpg
    [​IMG]



    The diagram below (drawn for a customer) corrects for the Beneteau bussed switch system and adds alternator to house bank wiring plus an emergency parallel (the old negative switch), dedicated & isolated start and house banks, full isolation of each bank and full cross over and an ACR etc...

    [​IMG]
     


    Leakie Marine and jssailem like this.
  9. AdamCermak

    AdamCermak

    Joined Oct 8, 2013
    26 posts, 0 likes
    Beneteau 321 1999
    US Rose Haven, MD
    The charts are truly great, thanks Maine Sail! I've not liked the wiring in my Bene 321 ever since we got her. I'm confused, thought: in the upgrade image, what's the hexagon lead, labeled "ALT"?
     


  10. Davidasailor26

    Davidasailor26

    Joined May 17, 2004
    1,508 posts, 350 likes
    Beneteau Oceanis 37 LE
    US Havre de Grace
    ALT is the output of your alternator, wired to charge your house bank.
     


  11. AdamCermak

    AdamCermak

    Joined Oct 8, 2013
    26 posts, 0 likes
    Beneteau 321 1999
    US Rose Haven, MD
    Thanks David, but I'm nevertheless confused. The drawing shows the negative lead going to negative busbar; positive to one side of ACR, and to where the starter battery lives; and "ALT" to the other side of the ACR, and where the house battery bank lives. So ALT needs to be positive; however, part of this design is to avoid a shunt between the two battery banks, so ALT can't be just another name for Positive. Any ideas?
     


  12. Gunni

    Gunni

    Joined Mar 16, 2010
    5,765 posts, 1,397 likes
    Beneteau 411 Oceanis
    US Annapolis



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