Forum Discussion

bka0721's avatar
bka0721
Explorer II
Jun 20, 2013

Installing a Blue Sea Disconnect SW for a FWS Battery Bank

Following the rule of always disconnecting the – (Neg) side first and then last when hooking back up, should this disconnect switch be installed in the – (Neg) line to break (switch) the load?

I always find it is better to ask here, a wealth of information available. (The + (pos) side is fused with a catastrophic 250amp fuse.) The bank is (8)6v 928AmpH.

In my monthly maintenance of my FWC battery bank, for my main solar array, I disconnect my important electronic equipment by turning off and disconnecting my 2000w inverter. This is done when I equalize the battery bank, each 1 to 1 ½ months. The inverter is easy to read and turn off, but the battery cable side is not in a convenient location to disconnect and the chance of dropping the nuts/lock washers is a common occurrence and they end up in a very difficult location to retrieve them. The cables are less than 36” long and the plan has always been to install a Blue Sea Disconnect switch. I now have the switch and would like to install it.

b

10 Replies

  • sum1's avatar
    sum1
    Explorer
    Jun 20, 2013
    I have always switched the positive side in boats and RVs. One reason is that I retain the option of leaving a radio memory/clock circuit, alarm, or (in the case of boats) a bilge pump hot.
  • time2roll's avatar
    time2roll
    Nomad
    Jun 20, 2013
    There is a hot and a ground. By convention we switch and fuse the hot. Ground is the frame.

    Yes when removing a cable from the battery for service it is recommended to remove the negative first. The only reason is to prevent the wrench from conducting the positive terminal to the frame.
  • bka0721's avatar
    bka0721
    Explorer II
    Jun 20, 2013
    RoyB wrote:
    I am assuming SW stands for Switch and FWC stands for FOUR WHEEL CAMPER which is a Truck Camper?

    I just love all of these acronyms... Not sure what FWS stands for.. Fish and Wildlife Service maybe...

    Roy Ken
    I feel your pain, as I move from one RV.net forum to another. Since I am posting in the Tech Forum I refer as one does here when referring to; Flooded Wet Cell' batteries (FWC). In the Truck Camper Forum it (FWC) typically refers to Four Wheel Campers. In electrical schematics SW refers to Switches. I did too many mechanical drawers in my younger life. As for; FWS, simply a non Techie Person trying to be Techie, with extremely fat fingers typing on a mobile device. A Flub.

    b
  • bka0721's avatar
    bka0721
    Explorer II
    Jun 20, 2013
    RoyB wrote:
    Be sure your BLUE SEA switch can handle all of that current. I think their contacts is rated at 300AMPS - would have to look...

    I always switch in POSITIVE side of things on the trailer... Each of my negative terminals goes to trailer frame ground so if I added a disconnect switch there I would also have to add some bus bars. I think the bus bars only come in four positions from BLUE SEA...Roy Ken
    Yes, Switch is rated for enough Amps. Since this is for a battery bank and not part of the electrical polarity of my camper (I have 3 independent electrical systems in my camper.) I don't have it grounded to my frame, but we are moving away from the question, a cable that comes from a large battery bank, to an inverter.
  • RoyB's avatar
    RoyB
    Explorer II
    Jun 20, 2013
    I am assuming SW stands for Switch and FWC stands for FOUR WHEEL CAMPER which is a Truck Camper?

    I just love all of these acronyms... Not sure what FWS stands for.. Fish and Wildlife Service maybe...

    Roy Ken
  • RoyB's avatar
    RoyB
    Explorer II
    Jun 20, 2013
    Be sure your BLUE SEA switch can handle all of that current. I think their contacts is rated at 300AMPS - would have to look...

    I always switch in POSITIVE side of things on the trailer... Each of my negative terminals goes to trailer frame ground so if I added a disconnect switch there I would also have to add some bus bars. I think the bus bars only come in four positions from BLUE SEA...

    Roy Ken
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 20, 2013
    I think Caterpillar is just a tad more intelligent than RV manufacturers, plus the YSB all wrapped up in a ball. I modified my first cabover camper "Kamp King" forty nine years ago. There is absolutely no advantage in breaking the positive side of a battery circuit*. I've seen many a commercial fishing vessel blow a foot wide hole in a 5/16" hull when the 32 volt system decided to make love to the "ground". The YSB is like the FAA, they are mired just as deep as the BCI.

    *Or please be nice to me and whisper in my ear "why"
  • bka0721's avatar
    bka0721
    Explorer II
    Jun 20, 2013
    Bob Landry wrote:
    I would like to see Doug Rainer chime in on this question, since he is a RV tech with 30something years under his belt. This has been heavily debated on every forum, and I have never seen an explanation for it.

    I work in the marine industry, and ABYC says put the switch on the positive side. Ever OEM builder that I know of puts it on the positive side, and when I do a 12V installation, that's where I put it. We do it that way because of the possibility of a large current load being drawn through wiring harnesses because of bad DC grounds, but I realize that RVs are not boats, and I would like to hear a reply from someone who actually know why and not simply an opinion or something that was written on the Internet.
    and this is why I pause and ask the question, where to put a disconnect switch.

    The one thing I would repeat here, is that I already have a catastrophic 250amp Fuse at the (+) Pos post terminal of my battery. This switch is doing nothing more than a switch does at a doorway to turn the light out, as you leave a room.

    b
  • Bob_Landry's avatar
    Bob_Landry
    Explorer
    Jun 20, 2013
    I would like to see Doug Rainer chime in on this question, since he is a RV tech with 30something years under his belt. This has been heavily debated on every forum, and I have never seen an explanation for it.

    I work in the marine industry, and ABYC says put the switch on the positive side. Ever OEM builder that I know of puts it on the positive side, and when I do a 12V installation, that's where I put it. We do it that way because of the possibility of a large current load being drawn through wiring harnesses because of bad DC grounds, but I realize that RVs are not boats, and I would like to hear a reply from someone who actually know why and not simply an opinion or something that was written on the Internet.
  • mbopp's avatar
    mbopp
    Explorer
    Jun 20, 2013
    I installed mine in the negative side, I figure there's less chance of doing any inadvertent arc welding that way!

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