confused about gauges

blueskies
blueskies Registered Users Posts: 54 ✭✭
ok, so help me sleep better.

this is a simple question but it applies to so many decisions

i have this 24 v solar bank (2 serial, 2 parallel) and all these huge wires  - see pic:

and don't razz me about the connectors - i'm on it despite these connector formats have served me well for years  

but if i need these huge wires to go to batteries and inverters, it seems like a 24 v led light panel like this would just short out and catch fire - see pic:


but it does not seem to mind the small wires including connection wires.  I DONT GET IT    I started down this path before and someone said i have to understand ohm's law.  I DONT but i've been wiring for years.

Comments

  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
    big and tiny wires together, right now, over me
  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
    I mean, heck, can I use well insuated speaker wire with appropriate fuses next to these huge wires??? - 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Blueskies, your pictures did not post...

    You size the wire for the amount of current you want to send from point A to point B.

    LED lights, may take less than 1 amp--So relatively small wire needed to carry current.

    A 12 volt @ 1,200 Watt AC inverter will take over 100 Amps @ 12 volts, so you need heavy copper wire to carry the current.

    You can look at the NEC for a quick estimate of wire diameter (AWG). Note, part of the carrying capacity is how hot the wire gets--The NEC chart is different amps for same gauge wire--Just higher temperature rated insulation, the hotter the wire can get, and the more current it can carry without melting the insulation.

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    The size of the wire itself does not change what happens with the load... For example, you could use 18 AWG (thin) or 2/0 (thick welding cable size) wire to the LED. The LED will draw the current it needs (LEDs are a "bad" example, they have other issues with voltage and current--Another post).

    The fuse is to protect the wire from overheating (too much load, short circuit, etc.).

    There are other limits--For example if you connect a 60 amp rated controller to a battery bank--The 60 Amp controller is rated to how much short circuit current it can take. The controller can take 60-80 Amps or so (if it shorts internally)... But if you fed it 250 Amps, it may blow a hole in the sheet metal housing and catch something on fire... Why you would not connect a 12 LED fixture to a 250 Amp 2/0 wire with a 250 amp fuse (the fixture would catch fire before the 250 amp fuse would ever blow).

    The other main thing to watch out for is voltage drop. The more current flows through a wire, the more voltage drop you have... And the longer wire you have, the more voltage drop too. For example, a 16 AWG extension cord may power your power saw at 10'. However, if you had to work 100' away from the outlet, you may need a 12 AWG or 10 AWG extension cord to supply current to the power saw without too low of voltage at the power saw motor.

    And the lower voltage circuits, you can only have low resistance from battery to load. It is very hard to send much current @ 12 volts from battery to a large load (like an AC inverter).

    For example, here is a chart of (estimated) fusing current for different AWG wire (copper, aluminum, etc.).

    https://www.powerstream.com/wire-fusing-currents.htm

    So the first step is figuring out the wires from A to B to C, etc... And what voltage the wire is running at and the maximum working current you expect it to carry. One you know those things, then you look up the size wire you need to carry that current (so it does not overheat), and the voltage drop (so you get sufficient current at the loads).

    Voltage drop calculator:

    https://www.calculator.net/voltage-drop-calculator.html

    The easiest way to understand this--Ask a question about a "real need" of yours (solar panels to charge controller, charge controller to battery bank, etc.) and step through the process.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
    Nobody made it sound so understandable before.  I have grown, thanks to your info.  Sincere thanks.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    My pleasure Blueskies.

    Sincerely,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset