any electricians out there?

Discussion in 'Community Discussion' started by rick snagwell, Dec 13, 2014.

  1. rick snagwell macrumors 68040

    rick snagwell

    Feb 12, 2011
    oceanside, ca
    i am setting up a solar system on my travel trailer.
    i have a 20amp tracer mppt solar charge controller. the + positive cable needs a fuse wired in it.
    instructions say i need a in-line fuse holder no more than 150mm.
    can anyone recommend via a link what this means.

    ive tried, just very confused and dont wanna mess the system up. thx
  2. Big-TDI-Guy macrumors 68030


    Jan 11, 2007
    Super late reply here - and I'm sure you've found the answer by now. But that 150mm distance is usually the maximum reccomended distance the fuse is from the battery terminal itself.

    Batterys often can be a source of power orders of magnitude greater than the wires attached to them can handle. So using a car as an example - where the ground (-) lead is usually attached to the chassis via a very thick cable. (4awg) Now if you were to run a thinner wire (10awg) to the positive (+) to power, let's say, a winch you've installed.

    Now if that new 10awg wire were to get cut or pinched against the chassis when you slam your hood shut, without a fuse, that wire is going to literally burn and catch itself and other things on fire. Let's say you DID install a fuse, but located it at the winch itself - you're car is still going to burn because the wire has no protection all the way up to that point.

    So by specifying how close the fuse must be located to the battery terminal, helps prevent this type of situation.

    Now before you go and bolt a fuse directly to the terminal of that battery in the thought of it being even safer - DO NOT.

    When fuses blow - they create an arc / spark. Most batteries over their normal operation generage explosive gases (pure hydrogen and oxygen) - in the perfect stoichiometric ratio for solid kaboom.

    Because of this, in passenger cars the closest fuses will be located inside a box shielding the spark from these gases - routed around 6-18" away from the battery itself. And the unfused power cable going from the battery terminal to this box, is usually kept as short as possible, and given additional protection to the insulation via split loom / additional tape to keep things from slicing into the insulation.

    So if you haven't already, mount that fuse close to the battery terminal, but outside of any "battery box" should you have one (a container where those gases typically builds up inside of). And use split loom / braided loom - on the wire going from the terminal to the fuse - just in case.

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