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What gauge wire to use? noob circuits

  1. Jul 16, 2017 #1
    2 sets of 6x LED strips, each 12v 8.1a 97.2W, powered by a single cv 240W PSU, in parallel. The 2 sets are split at the PSU end, each set getting 120W separately. Schematic below,
    2017-07-15 12.28.29.jpg

    What I don't know is what gauge wire to use at points A and B? Can you please explain what should be used and why?

    I looked at the AWG chart and I don't understand chassis wiring and power transmission wiring. What category do my wires fall under?

    Also, I haven't figured out yet how long exactly will my wires be at point A and B. I know length of the wire has some effect on the gauges, but don't know what effect. Can anybody please present a general guideline or pattern describing what happens as I increase or decrease my wire length?
    Much appreciated!
    Last edited by a moderator: Jul 16, 2017
  2. jcsd
  3. Jul 16, 2017 #2
    For what you are doing it would be considered chassis wiring. Power transmission wiring usually refers to the aluminum, or aluminum/copper clad wires used for high voltage transmission lines. I don't know what they are referring to in the above chart.

    What is a wire?
    • Conductor material (copper, tinned copper, aluminum, nickel, silver, etc.).
    • # of strands (1 strand = solid, as in house wiring, or multiple strands of lighter gauge wire, i.,e. - 7x32 is 7 strands of 32 AWG)
    • Insulation material (cloth, rubber, plastic, mica, etc.), thickness, temperature and voltage limits.
    What type of wire is appropriate depends on what it is used for. For instance, solid wire is fine for house wiring, but a very poor choice where a lot of flexing is involved. Spark plug wires have very thick insulation because they must operate at high voltage. Cloth covered, silicone rubber insulated copper wire is a good choice for motor leads, but TGGT or (Teflon-Glass-Glass-Teflon) or MG (Mica-Glass) nickel-alloy wire must be used inside industrial ovens, and other high temperature environments. A lot of it boils down to how hot the wire can be allowed to be. Ambient temperature matters, as does whether it is a single conductor in free air (good cooling), or multiple conductors enclosed within conduit.

    For 8.1 amps, 16 AWG copper covers all the bases, but for short runs in open air at room temperature you can get away with wire as small as 20 AWG.

    For each set of (6) 8.1A light bars, the wires to the power supply carry 48.6 amps.

    What I don't understand is how a 20A, 240W power supply will work with 16 light bars at 8.1 amps each (1166W).
    Last edited: Jul 16, 2017
  4. Jul 16, 2017 #3
    What would you recommend for my setup? How short exactly is a short run?

    To give some dimensions, the (A) 8.1a wire(s) will be 6-10 feet each, and the (B) 1.35a wires will be 10-15cm.

    The ambient temperature I don't expect to rise past 40C. Mostly, I expect it in the 25-32C range.
  5. Jul 16, 2017 #4
    Oh, I misunderstood.
    If each light bar is 1.35A, their 10 to 15 cm runs can be 24 AWG.
    16 AWG is still a good choice for 6 to 10 foot runs of the (A) wires.
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