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Not another Cable Size Thread :)

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  • Not another Cable Size Thread :)

    I have the a 350W Fusion Amp installed, only tested the power up, not fully installed:

    im running the following (untill told otherwise or i start a fire )

    Fused holder with 25Amp Fuse (~10-15cm) not sure of the wire guage (rated up to 30 Amps).
    8 guage from the fuse holder to Amp.
    Some Household (Green/Yellow) earthing cable running from ACC to switch near dash then to Boot, pretty ridged cored cable
    About 10cm max of the same earthing cable to chassis.
    Ok now for the questions:

    Is there anything wrong with the above?

    Im happy with the power, 8 guage should be fine, all fused close to battery with same size (25Amp) fuse that is in the Amp.

    Remote, again pretty happy with this, cant see it pulling many amps, this is just a signal cable right?

    Ground, here is my main concern, most things ive read said use the same size cable for ground, as you have for the power, now i usually would, but i ran out of 8 guage (which i can just buy more), but do i need to given the small distance it is running to ground.

    This is exactly the same situation of my Carpc, i have a smaller guaged fuse holder (10-15cm) to 8 guage and then back down to a smaller wire that came with the PSU (M2 atx), im using the PSU cable (smaller) straight to ground.

    Any advice will be greatly appreciated (as always).

    Last edited by RaptureOz; 03-21-2011, 09:15 AM.
    Corolla WorkLog

  • #2
    I dont know about how your PSU will react, but until I put some larger size cable on my amp it was really hot after only a few minutes of operation. I put some 10 gauge on it and it isnt even warm anymore.
    Car PC parts Purchased [90%]
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    Car Audio setup [60%]


    • #3
      As per mp3car FAQs: see the12volt's Recommended Power and Ground Cable Sizes & Speaker Wire Size and Length.

      Also BCAE's fuses.

      I think your fuse is too small (depending on voltage and max volume).

      Your cable may also be too small (depending on length).

      You could use the remote cable double the ground or power and use signal wire instead.
      DO NOT burn out the ground before the +12V (fuse or cable).

      You probably should use appropriate 12V cable.
      In some places, it is illegal to use domestic/industrial AC wire in vehicles (except for AC distribution).
      The insulation may also be different and may fail quicker (eg, vibration & friction).


      • #4
        Originally posted by OldSpark View Post
        You probably should use appropriate 12V cable.
        In some places, it is illegal to use domestic/industrial AC wire in vehicles (except for AC distribution).
        The insulation may also be different and may fail quicker (eg, vibration & friction).
        many times, the copper strands in houshold/industrial wire are much thicker and can cause some trouble later on once the copper starts to flex a little..

        i am not crazy about the smaller fuse-holder wire connecting to the 8ga in either case.. though given your current draw, i don't think it is very necessary to upgrade. though, if you were to ever upgrade your hardware, i would really recommend getting a 8ga specific fuse-holder.

        for the ground-- everyone makes a big deal about keeping the ground wire the same gauge as the power wire, and keeping the wire as short as possible. the reality is that as long as the wire is the same copper-diameter, or larger, then it should be fine.. lenth is a mis-portayed portion of the scale.. because the wire is longer there is more resistance-- so to combat that, use a thicker power wire.

        this is similar to pushing liquid through a straw-- the longer the straw, the larger diameter it needs to be to reduce the amount of resistance to blow out the liquid..

        but again, mobile-electronics power wire is going to be a better choice-- both for longevity, and in some cases, the wear resistance..

        for the remote wire-- same deal, though because this line rarely has more then 0.5A on it, it should not need to be any bigger then 18-16ga..
        My OLD 2001 Mitsubishi Eclipse GT:
        "The Project That Never Ended, until it did"

        next project? subaru brz
        carpc undecided


        • #5
          Soundman mentioned length = greater resistance.

          Whilst this impacts total voltage drop, it doesn't impact the fusing of the wire - ie, its current capability. I think many confuse the 2 issues.

          And for fairly short wires, the ends can act as heatsinks thereby allowing for greater current - the heat is conducted away before fusing occurs. But that is for SHORT cables where length may be 10x the cable diameter, maybe more.

          As for grounds being bigger than the hot cables, whilst the grounds should definitely exceed the hot fusing current (you want the hot supply to cease BEFORE losing your (main) ground connection!), I merely argue that increasing ground thickness can be a cheap way of reducing overall resistance. But that is because it is a shorter run, and therefore, a smaller resistance in the first place. (Maybe I've been trying to justify a more reliable ground thru wanky resistance arguments - or did I consider cable-to-ground connection resistances...? Oh - it's been to long!)

          PS - I'm reinforcing Soundman's reply... I no way do I mean to contradict....
          Last edited by OldSpark; 03-21-2011, 06:00 PM. Reason: PS...


          • #6
            Soundman/OldSpark thanks for your comments I appreciate them, I wasnt happy with the earthing cable it was more there to test and thought it may suffice once it was in, but i went shopping today, so hope you will be pleased .

            So am now running:

            From the battery 4 Guage into the car to behind the firewall with an 80Amp 4 Guage inline fuse close to battery, this goes to a 4 guage to 2*8 guage fuse block, from there i have one short section of 8G to the Carpc and a longer length of 8G to the boot, Ive replaced the remote cable with 16 Guage and the Ground wire is now 8 Guage.


            Corolla WorkLog