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Hmm... why an inline breaker in aux fuse block installs?

Discussion in '2nd Gen. Tacomas (2005-2015)' started by iroc409, Sep 19, 2011.

  1. Sep 19, 2011 at 4:13 PM
    #1
    iroc409

    iroc409 [OP] Well-Known Member

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    So, I am upgrading my aux fuse block from a cheapie 6-position to nice Bussmann waterproof relay/fuse unit.

    I bought an inline breaker, though it might be a tad small at 60 amps (still planning the circuits, and the fuse block only supports 80A anyway). However, I am kind of wondering, what does it really protect?

    The only thing I can see, is the relay center buss itself. Looking over the FSM's wiring guide, Toyota doesn't even use a main breaker/fuse/fusible link.

    So, it kind of begs the question... what's it good for?

    My current setup doesn't have one, but it's only had at most two forward auxiliary lights and my reverse auxiliary lights. I plan on adding a few extra things on this, though I'm not yet sure what all it will be.

    It seems like the primary scenario is if you are over-provisioning, of sorts. I.E., in my case, if I had 100A worth of circuits, even though the block is only rated to 80A. It would ensure I don't run too much at once, damaging the block. If I design the circuits properly though (not allowing more than 80A with all circuits combined)--which seems to be Toyota's take--it seems unneccessary.

    It seems one would be better served by a fuse (or fusable link) at the battery connection. My biggest concern is the cable coming loose, which the breaker doesn't really protect. However, Toyota doesn't do that, either (though the liklihood is probably very small with good fasteners and cable).

    What else am I missing?
     
  2. Sep 19, 2011 at 4:19 PM
    #2
    UndefinedTaco

    UndefinedTaco I'll eat all your food.

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    It's an 89 Toyota Pickup. I got some stuff done to it.. FJ axles going under it soon.
    In case of a surge, it'll kill the block power for saving the block..and saving your fuses on the block :D
    That's all..I don;'t think it's really required to fuse a fuse block lol..IMO.
    It does look cool seeing a 100A 12v breaker though mounted in an engine bay

    Peace of mind.
     
  3. Sep 19, 2011 at 4:38 PM
    #3
    skippermike

    skippermike Well-Known Member

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    Peace of mind for no fire.
    Having a fuse/breaker near to the power source (battery, alternator) will prevent a cable getting so hot as to maybe start a fire elsewhere in your truck, if there is a short.
    60 amp is probably good.
    I run power from engine battery to a charge combiner in back of the back seat, and to an aux battery, and then to aux outlets and to another 60 amp fuse for an inverter.
    If the inverter runs away, it will blow its fuse. If there is a short somewhere, the first fuse will blow.
     
  4. Sep 19, 2011 at 5:03 PM
    #4
    iroc409

    iroc409 [OP] Well-Known Member

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    I don't think a breaker would act fast enough (at least these breakers) to stop a surge from frying... whatever it is it will fry. As I understand, breakers can weld, are generally slow-acting, and overtime their ratings change. How much these happen though, is probably minimal.

    In most cases (including what I'm looking at), there's a 2-3' cable running from the battery to the breaker. If that comes loose, the breaker will not prevent a fire. I guess if something went wrong in the fuse block (something welded), then it would help, or if it were over-provisioned as I mentioned.

    I can see if you're running a large cable a long run, but you still almost have to have it close to the source.

    I thought Toyota's design of the headlight circuit is interesting. Power comes in from the battery cable to the power bus in the fuse/relay block. It goes straight to the headlight relays, and doesn't get fused until it is leaving the block to go to the bulbs. Not what I'm used to in circuit design, but then I haven't spent much time tracing around automotive circuits.

    Oh well, I should probably just put it in and stop over-thinking it. The location and design is easier without it (and I can claim fewer parts=less % chance of failure).
     
  5. Sep 19, 2011 at 6:44 PM
    #5
    joes06tacoma

    joes06tacoma Well-Known Member

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    You're protecting the truck from catching on fire if the main lead to your new fuse block touches ground or otherwise becomes overloaded.

    It is worth noting that there is a large cable going to the starter that is unfused from the factory.

    It's also worth noting that whatever length of cable from the battery to the input side of your new inline breaker will not be protected. Only the length after the breaker is protected.

    I have not done an aux fuse block on the Taco yet, but I have done two on previous trucks. The only place to mount the breaker was on the fender next to where the fuse block was mounted. That meant I still had a foot or more of unfused cable even with the breaker. I decided that there was no way I was going to overload the 4 gauge cable unless it became grounded somehow between the battery and the breaker. In that situation, the breaker would have done nothing to help the outcome. So I never installed it. I made sure the cable was secure and well protected and it became a regular inspection item when under the hood doing other maintenance.
     
  6. Sep 19, 2011 at 6:53 PM
    #6
    iroc409

    iroc409 [OP] Well-Known Member

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    I haven't checked the trip curves, just going by what I've read (which doesn't really come from any white papers). This breaker is a Bussmann, but I am pretty sure they are the ones that make Blue Sea.

    If my large supply wire shorted between the source and the breaker, the breaker would not prevent the short. Ideally, I should skip the breaker and install an inline fusible link. Or, use a fuse right at the battery. I don't have any tools to work with heavy-gauge wiring though, and am trying to go with off-the-shelf supplies.

    I'm not opposed to installing it. I paid $30 for the thing, just as well use it. I'm just questioning its utility, and whether the added complexity adds enough value to justify. It's probably a silly question at this point, though.
     
  7. Sep 19, 2011 at 6:54 PM
    #7
    iroc409

    iroc409 [OP] Well-Known Member

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    This describes precisely my dilemma! :D

    ETA: The cable from the battery to the factory fuse block also is not protected, nor is there a "main" fuse from battery to the rest of the system. There are main fuses connected to the charging system. Maybe they are intended to prevent alternator surge to the system? Or maybe preventing too high a draw from the alternator?

    My current setup does not have a fuse/breaker on the supply cable, but it's very well secured (even if the crimps gave out, it should not short). It's also only 10-GA, so maybe it would burn itself up before there's too much damage... maybe LOL!
     
  8. Sep 19, 2011 at 7:08 PM
    #8
    joes06tacoma

    joes06tacoma Well-Known Member

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    10 gauge seems too thin. I've never run 10 gauge with more than a 30 amp fuse. I know it's a short run, but seems sketchy. What I did on one truck was use my side terminal on the dual post battery to power the aux block. It's been a long time, but I think I just used an extra washer to compensate for the small 1/4 inch stud and oversized ring terminal. On the last one I did, I had a custom cable made at NAPA that had the correct size rings on each end to hook to the factory battery terminal and the small stud on my aux block. I knew that only way to burn up the 4 gauge cable would be to ground it, and the only way that would have ever happened would be in a wreck. Seemed like I was pretty safe.

    I used to install wheelchair lifts for custom vans and we always wound up with a foot or so of unfused 4 awg cable feeding the breaker under the hood. Many of these were later inspected by the county, city, school district, or whoever was buying the van. No one ever said anything about it, which makes me think there isn't a better way out there that is reasonably accessible.
     
  9. Sep 19, 2011 at 7:53 PM
    #9
    iroc409

    iroc409 [OP] Well-Known Member

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    10 gauge may have been a little thin, but it was only running two things: a pair of Lightforce 240's and my reverse lights. I don't think they were ever on at the same time, and I think each item was fused at 15 amps. I ran two wires/relays for each bulb (which was probably overkill, but it worked).

    NAPA makes custom cables? I didn't know that; that might be what I need.

    Is 4 gauge really needed though, or is 6 enough? I think on the wire charts it said 6 GA was good for 101 amps, and 4 good for 135 A. I won't be running more than 80 A, due to the fuse block buss ratings.
     
  10. Sep 19, 2011 at 9:46 PM
    #10
    anethema

    anethema Well-Known Member

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    How would the breaker not save your truck if you short the supply line to the fuse block to ground ?

    If you exceed the 80A or whatever (A short would blow 80A out of the water, no question.) it would trip the breaker. Even if the breaker took a second to let go, and it would be far quicker than this on a dead short, it would save your truck from burning to the ground.

    I also put in an Aux block (this is very old pick when it was first going in. More has been added and the whole mess cleaned up with loom etc).

    [​IMG]

    Hard to make out but I fused it with a 100A bluesea breaker. It can do no harm and while unlikely to happen, may save your truck.
     
  11. Sep 19, 2011 at 10:07 PM
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    joes06tacoma

    joes06tacoma Well-Known Member

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    I'm sure 4 gauge was overkill, but it was what they had in stock. Almost all NAPAs are independently owned. Our local one does do custom cables, don't know about anywhere else. I know they have to carry certain things, but have a lot of freedom to do whatever they want as an independent business. The owner of the NAPA here was at one time a Belden sales rep. Belden makes wire, cable, and connectors. So that may be something he chose to do independently.
     
  12. Sep 19, 2011 at 10:12 PM
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    joes06tacoma

    joes06tacoma Well-Known Member

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    I can see the breaker mounted on your fender to the right of the picture. The cable from your battery terminal to your breaker is not protected. Only the cable after the breaker. That's what I was talking about, and I believe the OP is talking about the same thing. The idea is why bother with the breaker if the most exposed part of the cable isn't protected.

    I have run cable through a breaker mounted on the fender, then run under the truck along the frame where it is vulnerable. The breaker is a necessity in that application. But if all you have is a foot or so of cable between the battery and the aux block, it really isn't doing any good unless you can mount the breaker right on the battery.
     
  13. Sep 20, 2011 at 7:17 AM
    #13
    anethema

    anethema Well-Known Member

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    True but if something in the fuse block shorted out somehow etc it would help. I Have been thinking of trying to move that breaker closer to the battery though to protect more cable.
     
  14. Sep 20, 2011 at 2:54 PM
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    JKD

    JKD Well-Known Member

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    Even if you've properly designed your fuse block, you may have enough capacity in the fuses to overload the input side of the fuse block. You have an 80 amp fuse block, if you had three thirty amp circuits on it and all three were running at the maximum current before the fuses blow, you'd be over the block's limit.
     
  15. Sep 20, 2011 at 4:04 PM
    #15
    iroc409

    iroc409 [OP] Well-Known Member

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    Yes, that's the only scenario I can see--as I mentioned, over-provisioning the circuits. I don't know that is "properly designed", though. I guess it depends how much power you need at once.

    It seems like 80A would be too much extra power to have running on regular concurrent devices.

    If I mount the breaker next to the fuse block, about my only choice is to get a local stereo shop to make me a 6" heavy-gauge cable--which is dependent on the maker's ability. Omitting the breaker, I can use a factory-made cable, which would seem a bit more reliable.

    I guess I need to look into my crystal ball and determine how much stuff I might install in the truck. To this point, there hasn't been much. There probably won't be in the future, the only main "if" is possibly some comm gear, and I don't know what it's requirements would be.
     
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