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Thread: How to determine wire gauge

  1. #1
    Registered Member chevynut's Avatar
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    How to determine wire gauge

    Don't use this chart from AAW!!!

    https://www.americanautowire.com/vie...tomotive-wire/

    How to determine the gauge (AWG) of automotive wire

    Make a small cut about 1/2″ long in the wire insulation and remove it. Count the individual strands of copper that make up the wire. Next, use a micrometer and measure one of the strands. Now use the following chart to determine the gauge of your automotive wire.


    7/ .028 = 20 AWG (7 strands that measure .028 each equals 20 gauge)
    16/ .030 = 18 AWG
    19/ .029 = 16 AWG
    19/ .027 = 14 AWG
    19/ .025 = 12 AWG
    19/ .023 = 10 AWG
    19/ .021 = 8 AWG
    37/ .021 = 6 AWG

    A quick glance tells you it's wrong. The individual strands get smaller as the wire size gets bigger. I wonder how long they've had that FAQ up.


    This one is better but has more variants:

    https://electronics.stackexchange.co...wn-wires-gauge
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension

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  2. #2
    Registered Member BamaNomad's Avatar
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    CN? Do you have and are you using a 'wire gauge' tool as shown here in this link? I happen to have one I inherited from my father ...

    https://www.wikihow.com/Gauge-Wire#G...anded_Wire_sub

    There's a pretty good definition of awg and how to calculate it here..
    https://en.wikipedia.org/wiki/American_wire_gauge

  3. #3
    Registered Member chevynut's Avatar
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    I don't have that tool and it looks like you still have to calculate the gauge, or at least count the strands. With the appropriate chart (Not AAW's ) you can just measure one strand with a caliper and count the number of strands.

    I can pretty much tell the gauge of most wires by looking at them, but sometimes 18 and 20 gauge look very similar. For the most part I have been using a caliper and measuring the overall diameter with insulation. It's a pretty good way to determine wire gauge on wires from the same source and same insulation type. I have found that 20 gauge is about .080", 18 gauge is about .090", 16 gauge is about .100" and 14 gauge is around .115". For smaller wires it doesn't matter much to me what the size is, because they're low current signal wires for the most part, not power wires. Also, when stripping the insulation my wire strippers pretty much tell me the wire size too. If I try to strip 18 gauge with the 20 gauge notch, it will cut some strands. If I try to strip 18 gauge with the 16 gauge notch, it won't cut all the insulation making stripping difficult.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension

    You can see my 56 Nomad build here http://www.picturetrail.com/chevynut

    For affordable C4 Corvette Suspension conversions for your car, visit http://www.classicedgedesigns.com

    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax

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    Most wire is stranded in geometric progressions of 6 because this is the way the stranding machines are tooled up. The same wire gauge is used for each individual strand.

    A single strand speaks for itself.
    The next progression is 6 strands around 1 for a total of 7 strands. The diameter of the stranded conductor is 3 * the diameter of a single strand.
    The next progression is 12 strands around the previous 7 for a total of 19 strands. The diameter of the stranded conductor is 5 * the diameter of a single strand.
    The next progression is 18 strands around the previous 19 for a total of 37 strands. The diameter of the stranded conductor is 7 * the diameter of a single strand.

    The cross sectional area (current capacity) is the strand area * the number of strands.

    If you were to draw this up to scale, you'd see that this puts strands in contact tangent to tangent everywhere with no gaps, packing the strands into the smallest overall package.

    Fewer, bigger strands will give you more cross sectional area of conductor and current capacity for a given overall gauge. More, smaller strands will give you more flexibility but less cross sectional area. That's why welding cable has so many tiny strands, it's for flexibility.

  5. #5
    Registered Member 55 Rescue Dog's Avatar
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    There are many other factors to consider for current carrying capacity of a conductor beside wire gauge, such as insulation type, temperature, and length.
    IMG_5344.JPGIMG_5345.JPG
    Last edited by 55 Rescue Dog; 03-15-2019 at 06:16 AM.

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    Registered Member BamaNomad's Avatar
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    Yes, temperature and wire length are factors wrt current carrying capability (but not insulation material!). But the TOPIC here is GAUGE and none of those factors have anything to do with wire gauge.

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    You start with wire gauge and construction. Insulation does not enter the picture for current carrying capacity. Voltage, temperature, and service conditions are what affects insulation choice.

  8. #8
    Registered Member 55 Rescue Dog's Avatar
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    You might want to look at the chart again. Current carrying capacity is affected by insulation, which also involves temperature, and has nothing to do with voltage. Also they are rated in free air, not all bundled up. Almost all quality wire has the gauge size, voltage, and temperature rating printed on it. Depending on the conditions, you need to go to the next bigger wire gauge even if the wire gauge is capable of carrying the amperage for the device, otherwise you can get a voltage drop, and as the wire gets hotter the resistance goes up.
    Last edited by 55 Rescue Dog; 03-15-2019 at 09:59 AM.

  9. #9
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    There are many other factors to consider for current carrying capacity of a conductor beside wire gauge, such as insulation type, temperature, and length.
    The thread is about determining wire gauge for a wire, not current capacity. And most of that stuff you're showing is irrelevant to automotive wiring. That's for single conductor building wires. A chart like one of these is much more relevant to automotive wiring ....I have a better one somewhere:



    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension

    You can see my 56 Nomad build here http://www.picturetrail.com/chevynut

    For affordable C4 Corvette Suspension conversions for your car, visit http://www.classicedgedesigns.com

    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax

  10. #10
    Registered Member chevynut's Avatar
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    If you look at a stock tri5 wiring harness you'll see that most of the wiring was done with 20 gauge wires. They worked fine, even for headlights. The charging circuit had some 12 gauge wires and there may have been some 14 or 16 gauge, but not much. Most of the stock wiring was sub-standard but it worked.

    I have a lot of electronic modules, relays, etc that take very little current (milliamps). I'm using 18 and 20 gauge there just because I don't have smaller wire and 20 gauge is already pretty small. When I originally put the harness together I used 14 gauge for the headlights because I planned to use halogen headlights....now I'm probably using LEDs everywhere so those big wires aren't really needed but I'm still using them. Taillights, park lights, brake lights, dome lights, etc. are all wired with 18 gauge. All of this is overkill now. The only places I need larger wires are the alternator, starter solenoid, fans, brake pump, fuel pump, power windows, A/C, and power seats.....only where there's large currents involved.

    I have a 160A alternator and I'm using 8 gauge wire from it to the starter solenoid (battery) and from the solenoid to the breakers that protect all of the power circuits. I have a 175A Midi-Fuse between the alternator and starter, and between the starter and the breakers...instead of a fusible link. The breakers are 50A and 30A. Fans go on a 50A breaker as does IGN power and Constant power. A/C takes a 30A breaker. Each circuit is then fused with an appropriate size fuse. Almost every module, and the A/C takes both constant and switched power. Not sure why it needs to be that way.

    Also keep in mind that the charts tend to be conservative...the wire will carry a LOT more current before it fuses or even gets warm. You don't want to generate a lot of heat or get too much voltage drop. I'm using the breakers for the alternator voltage sense point. The wiring lengths in a car are fairly short, compared to a building.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension

    You can see my 56 Nomad build here http://www.picturetrail.com/chevynut

    For affordable C4 Corvette Suspension conversions for your car, visit http://www.classicedgedesigns.com

    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax

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