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Technical what size fuse-able link wire to use?

Discussion in 'Traditional Hot Rods' started by birdman1, Aug 15, 2019.

  1. birdman1
    Joined: Dec 6, 2012
    Posts: 1,591

    birdman1
    Member

    I am wiring up my 1955 T-Bird and want to use a fuse-able link to protect the wiring. It has been converted to 12 volts, with a 1-wire GM alternator. I have a 14 gauge link wire off a 70's Ford that I want to use. I think the 14 gauge should work, any opinions? thanks,Henry
     
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Interesting question, I'd look over the wiring of the cars that used them, where they used them, etc...then duplicate it.

    But personally I'd rather run through circuit breakers.
     
  3. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,535

    Doublepumper
    Member
    from WA-OR, USA

    I believe GM used 14 gauge hypalon insulated wire.
     
  4. egads
    Joined: Aug 23, 2011
    Posts: 1,419

    egads
    Member

    You could wire thru a Maxi-fuse ( or several ), put it somewhere easy to get to if needed, done several cars with this setup.
     

  5. Blake 27
    Joined: Apr 10, 2016
    Posts: 1,504

    Blake 27

    I also recommend a Maxi-fuse, a fuse-able link burns when overloaded and could cause a fire.
     
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  6. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,422

    OLDSMAN
    BANNED

    Most wiring companies recommend circuit breakers. Fixable links haven’t been used by auto makers for years because of fire problems.
     
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  7. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 6,079

    scrap metal 48
    Member

    I too would use a maxi-fuse...
     
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  8. Ziggster
    Joined: Aug 27, 2018
    Posts: 1,697

    Ziggster
    Member

    My 97 Toyota LX450 uses fusible links as does all 80 Series Land Cruisers from that era right next to the battery for the main wires going to the fuse box. I've heard of no one changing out the fusible link for circuit breakers. In fact Toyota still sells them as spares. Yes, not as good as a circuit breaker but still good as a fuse in terms of performance. Only issue is when it goes, you better have some spares.
     
  9. Ziggster
    Joined: Aug 27, 2018
    Posts: 1,697

    Ziggster
    Member

    Here you go...
    image.jpeg
     
  10. A fusible link is basically a means by which the manufacturers can 'cheat' on wire size, saving them a few cents per harness. I don't recommend them, as sizing one correctly is all but impossible with the information the usual home builder has. There's multiple good reasons why they aren't more widely used.

    What specific wire are you protecting, i.e. to/from what? What wire gauge is it? What's the connected load?

    You might want to read through this... https://www.jalopyjournal.com/forum/threads/wiring-101.843579/
     
    Last edited: Aug 16, 2019
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  11. G-son
    Joined: Dec 19, 2012
    Posts: 1,277

    G-son
    Member
    from Sweden

    Use regular fuses, easy to find the right size for the wiring it feeds.
     
  12. Ziggster
    Joined: Aug 27, 2018
    Posts: 1,697

    Ziggster
    Member

    I agree that a fusible link probably shouldn't be used by the hobbyist unless they are well versed with automotive electrical knowledge, but as far as automotive manufacturers using them to save a few cents on wire size, I'm not so sure. I can only speak from what I know about my Lexus, but Toyota engineered that vehicle for a 25 year life span, and the quality and attention to detail is second to none. I believe in 97, it cost USD$50K, so I doubt very much the use of a fusible link was to save a few cents.
    I do have many years experience designing and building large HVAC systems for the inner-city bus and highway coach markets, and we took every possible measure to ensure the electrical systems were spec'd and built properly to avoid any potential issues that could lead to electrical shorts and possibly a fire. For my HVAC systems we spec'd EATON circuit breakers for all electrical motors and LittleFuse blade style fuses for everything else. Watch out for cheap imitation LittleFuse fuses. Only use genuine LittleFuse products.
     
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  13. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    If you can find it, someplace on the Ron Francis Wiring site, watch what happens when a fusable link catches fire. I would never use a fusable link in any of my builds. Use a fuse as others have suggested. If you have an issue you simply change the fuse. With a fusable link, after you put out the fire and replace all the burnt wires you need to replace the link. A lot easier to replace a fuse especially on the side of a major highway.
     
  14. birdman1
    Joined: Dec 6, 2012
    Posts: 1,591

    birdman1
    Member

    will a circuit breaker or maxi fuse break the circuit as good as a fuseable link in a condition where there is NOT a sudden short circuit, but only an overload that slowly heats the wiring in the car?
    bet you figured out already i am not a spark chaser by trade! thanks for the help.Henry
     
  15. Short answer, no. That's the primary usage of fusible links, but again, you have to know what the total connected load is, the size of the wire you're trying to protect, and how long the overload will occur in order to size the link.

    The big problem for a DIYer is there's zero information available on current slope for fusible links. In other words, how much current vs time does it take before the link clears the fault.

    It's pretty much cut-and-dried for fuses/circuit breakers. A fuse will go open once current hits it's rating, give or take a few percent. A bi-metal type circuit breaker can tolerate an overload a bit longer, but will still go open at max rating within a short period, faster at overload.

    If you have a wire that you expect to see regular overload on, it's generally better to simply increase the wire size to handle the max load, then use the appropriate fuse.

    If it's a feeder wire (feeding multiple circuits, all with their own individual overcurrent protection), I wouldn't bother with protection, simply route the wire for mechanical protection from damage and don't worry about it. That's what the OEMs usually do. If the anticipated overload is enough to give you pause, you need bigger wire.
     
  16. G-son
    Joined: Dec 19, 2012
    Posts: 1,277

    G-son
    Member
    from Sweden

    This might be interesting to some. Fuses don't blow at exactly the current they're rated at, rather there's a big time difference depending on how large the current is. A small overload may last quite a while, a big overload blows it FAST. This type of info should be available for any kind of fuse.

    upload_2019-8-16_23-18-4.png
     
  17. Keep in mind that EVERY circuit has current inrush. On most it's small/quick enough to ignore (motors being the main exception), but that can skew current demand curves. As an example, a typical 1157 lamp will measure about 2 ohms through the brake filament when de-energized which calculates out to about 6 amps via ohm's law, but only draws a bit over 2 amps once up to operating temp.
     
  18. birdman1
    Joined: Dec 6, 2012
    Posts: 1,591

    birdman1
    Member

    The 1973 mustang I took the 14 gauge fuse link off of was the wire going from the alternator to the battery post on the solenoid. Does Ford still do that
     
  19. I don't recall them doing it then; you may have something somebody added.

    There's five wires and/or circuits I won't install overcurrent protection on.
    1. The alternator output to battery. Alternators (and generators) will fail 'open' almost always. Even if one manages to short to ground, all damage will be inside of it, an external fuse won't do anything.
    2. Ignition system. Ignition systems are designed to short to ground (that's what fires the coil) and also usually fail 'open'.
    3. Starter solenoid. Another circuit that will fail open.
    4 and 5. Power feeds from the battery to the switched and unswitched halves of the fuse panel. If it's wired right, all circuits connected to the panel except 2 and 3 above will have their own overcurrent protection on each individual circuit.

    The OEMs typically didn't fuse these wires/circuits on HAMB-era vehicles. As long as the wire is routed to protect it from physical damage, they shouldn't need anything more. Overcurrent protection on charging system output and fuse panel feeds are very difficult to size because the loads can vary so widely. Basically about all you can do is fuse them large enough to cover whatever the max load or output would be, but all you're really getting is catastrophic short circuit protection. A fusible link will probably combust at about the same time as the wire if it's big enough to carry the load.

    Now, if you're using a lot of modern electronics, this may not be true, but we're not talking HAMB-correct stuff anymore...
     
  20. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 2,269

    woodiewagon46
    Member
    from New York

    Another issue with fusable links is as I understand it, is this. The entire circuit must be wired with a fireproof wire. It makes sense. If you have a fusable link with the special fireproof, Hypalon wire, you can't use some ordinary wire from some auto supply to complete the circuit. The ordinary wire will be on fire before the link opens.
     
  21. BamaMav
    Joined: Jun 19, 2011
    Posts: 6,711

    BamaMav
    Member
    from Berry, AL

    Ford still uses a fusible link in the alternator power circuit, my 99 F150 and 05 Expedition both have one.
     
  22. Do it Over
    Joined: Dec 25, 2017
    Posts: 478

    Do it Over
    Member
    from NYC, NY

    IMO a fuse is much better and safer not to mention easier/faster to replace.
     

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