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Battery Disconnect Switch: before or after Catastrophic Fuse?

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  • Battery Disconnect Switch: before or after Catastrophic Fuse?

    Been searching a couple hours, including here, but didn't find anybody discussing the question.

    Putting the "catastrophic" fuse as close to the battery as possible is well-documented; any wire before the fuse isn't protected so you want it short and ideally in conduit. I get that.

    It seems there is a risk, when using a tool on the hot-side hardware of the fuse holder, of accidentally grounding the handle (especially in an RV with cramped space). In that event there would be no OCP. If the battery disconnect were upstream of the fuse, the user could de-energize the whole fuse holder -- but that would mean even more unprotected cable, plus the switch itself and two cable terminations, upstream of the fuse an unprotected. Is the fuse-replacement risk just part of the general risk of electrical work, or should it be factored in? Are there other requirements for clearance or access in place that are meant to address it?

    I read a portion of the AYBC code (11.10.1.1), as well as sections 240, 551, 706, 710 of NEC 2020 online but didn't spot any explicit guidance. However, I realize it takes a lot more than a simple pass through of a few select sections to really understand the Code. So I was hoping y'all might be able to offer some clarification.

  • #2
    There are completely insulated tools for removing fuses (fuse pullers). That seems the best solution, but I haven't studied code on this either.

    Once, I accidentially shorted across a full-size car battery and it made sparks, but didn't destroy anything. I'm not recommending doing that, of course.

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    • #3
      Originally posted by bob-n View Post
      There are completely insulated tools for removing fuses (fuse pullers). That seems the best solution, but I haven't studied code on this either.

      Once, I accidentially shorted across a full-size car battery and it made sparks, but didn't destroy anything. I'm not recommending doing that, of course.
      I know that NASCAR use a high amp disconnect switch as their primary battery shut down. I think you can get one from most auto-part shops. But again how you run the wire and its size would have to be determined by you.

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      • #4
        The 300A terminal block fuse is a bolt on fuse, not a spring tension grip
        https://www.bluesea.com/products/215...k_-_30_to_300A
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        • #5
          Yeah, I don't think I've seen a 300A fuse you can pull with a puller...and don't think I'd want one either, for the sake of resistance. Those BlueSea terminal fuses are slick; I used one in a previous battery bank...but that's actually part of the history of this question -- even though they have zero unprotected cable, there's still the tool-shorting-to-ground question, if you're replacing the fuse.

          I guess shorting a tool to ground is a risk anytime you're working on the battery at all, so maybe that just falls under the same umbrella; no code can fully protect against being stupid while working on your system...?

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          • #6
            If the fuse is blown, there is no current ... disconnect the negative lead, replace the fuse, reconnect the negative lead. With the lead disconnected, an accidental short to "ground," or frame in a car is a non-event. OF COURSE, to the negative battery connection is still an issue.

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