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How to determine wire gauge.

Discussion in 'Electronic Basics' started by Tibur Waltson, Jan 30, 2004.

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  1. I salvage electrical wires from dishwashers, cars, and
    heaters. I keep only the ones that can power large motors,
    fans or anything that demand high current and power.
    The wires look and feel the same but actually are not.
    They, except a few, cannot drive a car radiator fan
    longer than a couple minutes without heating up or
    sometimes melting.

    I don't have fancy gadgets to determine which wires
    are which but I like to know which ones can handle a
    simple load as a radiator fan. How do I determine the
    wire gauge when they look the same?

    TIA, Tibur
  2. Pick up a cheap micrometer or a dial caliper to measure the diameter
    of the wire, and look it up on a wire chart..
  3. Bob Masta

    Bob Masta Guest

    Even cheaper, you can close-wind a number of turns on a
    pencil or something, and measure the packed total length
    with an ordinary ruler. Divide by the number of turns and
    you've got the wire diameter, then look it up on the chart.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  4. Bill Vajk

    Bill Vajk Guest

    It is the cross sectional area of the conductor itself
    that matters, not the overall diameter including the

    Herer's a quick fix for your problem. Hook up your wire to
    the load and try running it. If it starts to get warm, add
    a second in parallel and try again. Keep adding parallel
    conductors till they do not heat up.

    The wire is free, after all, so you can use as many as you
    would like.

    Here's a chart about wire gages. You might find a friendly
    soul someplace who might cut you some sample pieces which
    you could label and mount so you have something to use for

    As you can see the larger the number the smaller the wire.
  5. Bill Vajk

    Bill Vajk Guest

    Modern appliances sometimes use small wire with a thick
    insulation, and he's slavaging the stuff out of
  6. I have carried a micrometer in my toolbox for over 30 years to check
    wire and sheet metal gauges. I also have a 6" dial micrometer to measure
    larger parts. The pair cost less that $20 these days, and are handy for
    other jobs. You only need to strip a 1/4" of the insulation to measure
    the wire with either of these tools.
  7. The problem is that the cross sectional area look
    the same after I strip a 1/4" of the insulation.
    The problem is that it takes a long time to heat up (five
    minutes.) I have 100 wires, so that'll take 500 minutes.
    What if I remove a single strand and test how long it
    burns up with a 600-cranking amps battery?

    Good link, good advice, thanks to all.

  8. John Fields

    John Fields Guest

    The problem is you're a fucking idiot.

    _Measure_ the diameter of the wire, then use a copper wire table to find
    the gauge.
  9. Here, take a look at some wires I scanned.

    Actually, what I wanted to say this bare wire measures 2.2 cm in
    diameter will not heat up. But when I use two 1.5 cm
    diameter bare wire (not shown in the pic) they heat up
    compared to a single 2.2 cm wire. What is happening?
    Nice use of a discriptive verb. I had the belief that the diversity of the
    wires that I collect from would be made up of various
    materials. Some withstand heat, some won't. Some come with
    poor conductivity, which generates heat. Or is that a myth.
    But if what you're saying is true, that all wires are made the same
    material, then I'll just get a micrometer, which I'll eventually do.

  10. Bill Vajk

    Bill Vajk Guest

    Let's get the units right. 2.2cm = 1 inch.
    How about a guess of copper vs. aluminum?
  11. 1 inch is defined as 2.54cm
    The resistance of wire is inversely proportional to its diameter. As gauge
    decreases, diameter goes up, so resistance goes down. Resistance = heat
    given the same current.

    Here are some fun wire facts for solid wire.

    Here is the formula for the diameter of a wire, given the gauge G:

    ( 83690 )
    D = sqrt(-------------)

    D is in mils (which are 1/1000 inch)

    The resistivity of solid wire depends on the temperature, and the specific
    resistance (rho) of the material the wire is made from. Here is a list of
    specific resistances and tempcos (alpha) for various common wire materials:

    (View with fixed width font, such as courier)

    rho alpha
    Aluminum 17 0.004
    Copper 10.4 0.004
    Gold 14 0.004
    Nickel 52 0.005
    Silver 9.8 0.004
    Tungsten 33.8 0.005

    The resistance of a length of wire can be computed from the following

    R(T,G,rho,alpha,l) = rho * l * 1.26096^(G-1) * (1 + (T - 20) * alpha)
    rho at 20C, l in feet, T in C.

    Bob Monsen
  12. Bill Vajk

    Bill Vajk Guest

    I swear I pressed the ~, sorry.
  13. Here's the correct units.

    2.200 millimeters [mm] or, 0.08661 inch [in] or ~ 12-11 AWG

    1.500 millimeters [mm] or, 0.05906 inch [in] or ~ 15 AWG

    What will (15 AWG)2 be equal to? My guess is 11 AWG?

    If anyone knows how to calculate diameters correctly, (please help).
    If the 15 AWG is found to be an inferior conductor, I will throw them
    out. Or has Robert and Bill already provided the answer. . . ?
  14. Bill Vajk

    Bill Vajk Guest

    When the wire is free, parallel as many as you need to.

    As far as equivalent diameters go I don't think you need to
    work it out doing the math if you don't want to bother. Use
    tables like

    Simple multiplication yields two #15 wires equate to about
    one #12 so long as they're the same material.
  15. Steve Dunbar

    Steve Dunbar Guest

    The rule of thumb to find the equivalent of two wires of the same gage is to
    subtract three from the gage number: 15 - 3 = 12 AWG.
  16. The problem is now SOLVED. :) I can now conclude that I
    actually have an inferior conductor. The #12 came from a
    BMW while the #15 came from a Honda. A micrometer
    will be useful in this case.

    I was tossing and turning in bed thinking I wouldn't find a
    solution. Now I can sleep. THANKS to all.

  17. Thanks once more. I want to apologize to Mr. Fields. I didn't
    meant to say that his verb is too descriptive. Because my parents
    and teachers are teaching us not to talk about sex and swear, I
    admit I'm a little naive and unfamiliar with American English or
    newsgroup posting schemes.

    Anyway, more happy news, I acquire a digital caliper
    which measures in increment of 0.0005, 0.0010, 0.0015", etc.
    So, is useful, including the Copper wire gauge table.

    I also borrowed a book from a friend, "Electronic Fundamental
    textbook, from Prentince Hall." and will read 90% and will understand
    70% .

    Now that I have these off my guilt list, I can relax..... Thank you
    everybody being patient, for reading, and for being extremely
    helpful and knowledgeable.

    Best of luck,
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