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Adding Fuses and Amperage

Discussion in 'General Electronics Discussion' started by Hollywood28, Oct 2, 2014.

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  1. Hollywood28


    Oct 2, 2014
    Hi all,

    I have a feeling that my question is probably easy to answer (please bear with me), though I have searched everywhere on the web and cannot find an answer.

    I am installing a radar detector in my vehicle that requires 12V. I am looking to tap the fuse box with a product called Add-a-Circuit by Littelfuse . The product offers a clean installation without having to splice wires. You are able to turn one fuse slot into two, while giving protection for both circuits. It says that it, "Uses ATO fuses up to 10 amps".... Though this is where it gets tricky. Does this mean that I cannot exceed 10amps when BOTH fuses are in the module (i.e. the fuse that was originally there + the amperage of the fuse you will use to protect your additional device?), Or does this mean that whichever device that I will be adding (which happens to require a 6 amp fuse) cannot exceed 10 amps once it shares the line with the original fuse I have split?.... OR does this mean that neither fuse can exceed 10 amps (the original which you will be tapping or the new device's)?

    Any and all help is greatly appreciated. Thanks.
  2. davenn

    davenn Moderator

    Sep 5, 2009
    welcome to EP :)

    I read it an you cant exceed 10A on either fuse

  3. Gryd3


    Jun 25, 2014
    I second that.
    They would not provide 10A fuzes if the entire assembly could only handle 10A would they?
  4. Hollywood28


    Oct 2, 2014
    I know, that's what I thought too, but I wasn't sure. I read the product explanation more than once, and I cannot find where it explicitly says that the 10 amp rule is per fuse. In the picture they show a two 5-amps together, and that is what made me question the whole thing.

    I agree with Gryd3, why would they include a 10 amp? I mean, you could technically just find an empty 10-amp slot and stick one 10-amp fuse in there to cover your add-on accessory.

    If anyone has time, could someone please explain in technical terms why this system allows for a 10 amp limit per fuse?

    I am not an electronics aficionado, though right now I wish I was! :rolleyes:
  5. Gryd3


    Jun 25, 2014
    Only reason I can think of would be limitations imposed by manufacturing.
    The electrical joints, conductor quality, insulation quality... they are all a factor. Without knowing what factors they considered it's hard to tell if the entire assembly has a maximum of 20A, or if each position has a maximum of 10A. (The difference could allow a 15A, and a 5A to be used for example...)
    davenn likes this.
  6. chopnhack


    Apr 28, 2014
    I'd like to point out that you can not exceed the max allowed by the original wire serving the feed. In other words if the wiring harness that feeds that fuse is capable of only 10 amps then that is your total max allowable to be used at once. Some auto's have wiring harnesses that have fusible links, or wires that act as fuses if a max amperage is exceeded. Does the radar detector not have an option to use the cigarette lighter? I know many newer vehicles don't have one of those, but some still have it as an aux. power source. Hope this helps.
    Gryd3 likes this.
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