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How do you know if a ground connection is right? And how to properly branch circuits?

Discussion in '3rd Gen. Tacomas (2016-2023)' started by Rujack, Jun 29, 2019.

  1. Jun 29, 2019 at 7:22 PM
    #1
    Rujack

    Rujack [OP] Stop Global Whining

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    I mean, I could just use any old 30’ piece of 20 gauge speaker wire and stick it into the ground pin on my trailer harness and that would ground a 50amp 12v circuit. At least for a second. Couldn’t I? But that would be all wrong and dangerous, and sloppy as hell.

    So how do you know if a ground connection is sufficient?

    I’m putting a 6 circuit fuse box in my bed. I’ll be running 6awg (which will rate this circuit at 50amps) from one of these

    Blue Sea Systems Dual MRBF 30 to 300A Terminal Fuse Block https://www.amazon.com/dp/B002INJXO6/ref=cm_sw_r_cp_api_i_QLbgDbK5XJCAQ

    to the fuse box. What’s the closest place to ground the box? Ideally, since my plan at the moment is to mount the box to my bed rack, I could just ground it right to the rack. But the only possible way that I can see how the rack might have a ground path is through the steel part of the bed near the tail gate, to which my bed stiffeners are fastened.

    Basically rack > steel part of bed > bed stiffeners > frame.

    Is this ok? It seems a little janky.

    Also, how does one use a multi meter to test the integrity of a ground? Is that even a thing?

    992611AB-5352-4C19-9935-1D50C552D6C5.jpg
    B924B928-4DC6-454F-B98B-D8DFAE0F50D2.jpg
     
    Last edited: Jun 29, 2019
  2. Jun 29, 2019 at 7:28 PM
    #2
    slowtacotruck

    slowtacotruck Well-Known Member

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    You can check for voltage drop between the thing you are grounding and the negative battery terminal. Another indication it's not grounded well is that the terminal end is glowing.
     
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  3. Jun 29, 2019 at 7:33 PM
    #3
    Rujack

    Rujack [OP] Stop Global Whining

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    Ok, so neg lead of the meter on the neg battery terminal and positive lead on the positive of device? What am I looking for?
     
  4. Jun 29, 2019 at 7:35 PM
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    Skydvrr

    Skydvrr IG: @kalopsianick

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    Negative lead to negative on batt, positive to whatever the ground point would be. Like u can do a voltage drop from alternator ground to battery negative ground and measure voltage drop of all the wiring/connections from every point in between.
     
  5. Jun 29, 2019 at 7:43 PM
    #5
    Rujack

    Rujack [OP] Stop Global Whining

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    Ok that makes sense. And what would be acceptable / good?

    Edit: so with meter setting on dc volts I’m looking for voltage drop of how much? And is this is going to tell me if the ground sufficient?

    As you can see I’m not too savvy in this department.
     
    Last edited: Jun 29, 2019
  6. Jun 29, 2019 at 8:04 PM
    #6
    LSUfan1975

    LSUfan1975 Well-Known Member

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    Just ground it to the beer cans back there.

    Kidding. 10% is the maximum acceptable for voltage drop. So a 1.28v difference. That being said the lower thebetter
     
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  7. Jun 29, 2019 at 8:06 PM
    #7
    Rujack

    Rujack [OP] Stop Global Whining

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    Haha. Yea it’s still got some left over camping back there...

    Excellent thanks!
     
  8. Jun 29, 2019 at 8:09 PM
    #8
    s4nsc

    s4nsc The chicken stays…

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    Measure resistance from the frame (bare metal) to your potential ground point. Should be less than 1 ohm.
     
  9. Jun 29, 2019 at 8:10 PM
    #9
    Rujack

    Rujack [OP] Stop Global Whining

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    Ok good. I was wondering about this too. Good to have both data.
     
  10. Jun 29, 2019 at 8:14 PM
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    slowtacotruck

    slowtacotruck Well-Known Member

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    Resistance checks are good but with voltage drop you check it under load so it is a better representation of the condition of the circuit.
     
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  11. Jun 29, 2019 at 8:23 PM
    #11
    s4nsc

    s4nsc The chicken stays…

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    Ground is your point of zero potential. If the point you want to use is truly grounded there should be no difference in potential (voltage) between a known ground and the one under test.
     
  12. Jun 29, 2019 at 8:46 PM
    #12
    Rujack

    Rujack [OP] Stop Global Whining

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    Zero potential might be the best way to think of ground I’ve heard. That makes the math clear as day.

    I just checked resistance between the rack and frame and I get between .1 - .2 ohms. I’ll do a load test when I get the ends crimped on the wires tomorrow. Knock on wood.
     
  13. Jun 29, 2019 at 9:01 PM
    #13
    Mtn Mike

    Mtn Mike Well-Known Member

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    Actually the right way to assure that the negative side of your circuit is adequate is to run an identical lead as your positive directly to the negative terminal on your battery. Ideally run it adjacent to your positive lead. The only difference will be that your positive lead is red, and runs to your aux. fuse box and the negative lead is black, and runs to some kind of ground bus. Then you can run negative leads from the ground bus to the individual devices. No part of your truck (frame or body) will give as good of a connection as a quality lead run to your battery. Also, the term "ground" is confusing. The term ground has like 10 different meaning depending on the application. It doesn't work the same way as a ground in your home electric system.

    Edit: It also depends what you're planning to run on the circuit. If all you're running is a couple LED lights, then a frame ground would be fine. However, since you're running a 6 gauge positive lead, I assume you plan to run some high current devices. Again your best bet is run a 6 gauge negative lead to your battery. That way you're assured that the positive and negative side of your circuit are fit for same amperage draw, and have the same voltage drop.
     
    Last edited: Jun 29, 2019
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  14. Jun 29, 2019 at 9:39 PM
    #14
    Rujack

    Rujack [OP] Stop Global Whining

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    Also. What is the right way to branch (i think I heard it called that somewhere) a circuit?

    I currently have the three comms radios in my truck:

    50w 2 meter / 70cm
    25w 10 meter
    40w 10/11 meter

    Iirc, the 2 meter and 25w 10 meter are each fused at 20amps, and the 10/11 meter is fused at 10amps. I don’t know if I can substitute this info for the actual amp draw though (I can look tomorrow. Too lazy right now).

    These are wired individually to a 6 circuit Blue Sea fuse box w neg bus, located about 10” from the battery. I want to clean things up a bit so was thinking I might put a fuse box for them under the dash. And although I can’t see myself transmitting on all three simultaneously :)notsure: :burp:, you never know), it seems like I should still run a 50 amp circuit. Or more accurately, a circuit equal to (or greater than?) their combined maximum draw. Right?

    So I want to do that, and add the aforementioned 50amp run to a 6 circuit fuse box located in the bed. Which will immediately have a fridge @ 10 amps, later, likely some lighting, and if I find myself still with any time to spare, a submersible heating element (guessing around 150w). Edit: will most likely be adding OBA to this circuit.

    AND, I want to be able to add more later. Just in case.

    So how should I do all that?

    So far, I’ve come up with the following:

    Either these:
    https://www.ebay.com/ulk/itm/202137133758

    with breakers on a panel somewhere near the batttery;

    or this fuse block:

    Blue Sea Systems Dual MRBF 30 to 300A Terminal Fuse Block https://www.amazon.com/dp/B002INJXO6/ref=cm_sw_r_cp_api_i_pPdgDbRX4P51W

    but that will only give me two circuits, and it’s almost as much as two breakers once I buy the fuses. And the fuses are expsensive. And it doesn’t look organized.
     
    Last edited: Jun 29, 2019
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  15. Jun 29, 2019 at 9:51 PM
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    Mtn Mike

    Mtn Mike Well-Known Member

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    You really need to start by figuring out what you're going to want on the circuits and calculating the amperage requirements. As for the radios, unless you're planning to transmit on all three radios at the same time, you'll be fine budgeting for 20 amps for all three of them. Your fridge will only draw a few amps. Based on what I'm hearing you don't have a very high current demand. Blue Sea makes some quality stuff. I run similar accessories as you and use this box under my hood:

    https://www.amazon.com/dp/B000THQ0CQ/ref=emc_b_5_t

    It also has a negative bus built in.
     
  16. Jun 29, 2019 at 9:54 PM
    #16
    Rujack

    Rujack [OP] Stop Global Whining

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    I was initially going to do that but it doubles the cost of the wire. Some have suggested this, others have said the frame would be ok.

    So it does sound like the right way to do it is to run the neg back to the battery. Oh well. Thought I could save a few bucks...

    What is it called, if not “ground”?
     
    Last edited: Jun 29, 2019
  17. Jun 29, 2019 at 10:01 PM
    #17
    Mtn Mike

    Mtn Mike Well-Known Member

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    Based on the devices you've listed, I think you can get away with much thinner wire. 40 amps should be more than adequate for radios, fridge, and some area light. So, you shouldn't need any more than 8 gauge wire depending on how far the wire run is. In this case, building your circuit with "room to grow into" may cost you significantly more in wire. Wire size chart:
    http://www.aic-controls.com/wire-size
     
  18. Jun 29, 2019 at 10:03 PM
    #18
    Rujack

    Rujack [OP] Stop Global Whining

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    Yep, that’s the one I have under the hood. And got another today for the bed.

    Well, so far just the stuff I mentioned: fridge, maybe heating element, likely air compressor, likely LEDs. Ultimately, the biggest draw on this circuit I imagine would be the compressor at ~25amps...
     
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  19. Jun 29, 2019 at 10:04 PM
    #19
    Rujack

    Rujack [OP] Stop Global Whining

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    I considered 8awg but wanted the headroom. Plus I already bought it.

    The fridge and LEDs will be on the bed circuit. The radios will likely be on a dedicated circuit under the dash.
     
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  20. Jun 29, 2019 at 10:06 PM
    #20
    sd1uh8as

    sd1uh8as Well-Known Member

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    I ran my Viair 400p to the bedside of my long bed using 8awg wire. That compressor only pulls maybe 40A but I like giving margin of error.

    I also have a fridge in the bed that pulls maybe 10A. I ran a 12v+USB that in total, pulls around 20A to the bedside. Used 10awg wire for that one.

    All negatives are ran to the battery.
     

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