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#### tmcdanel

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I have some 50' & 100' extension cords that are not labeled well (the gauge is not printed on the insulation) and I want to know their gauge.

How many ohm's is a 12 gauge 50' cord?
How many ohm's is a 14 gauge 50' cord?
How many ohm's is a 12 gauge 100' cord?
How many ohm's is a 12 gauge 100' cord?

#### RAL238

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You can find resistance values here. Note that they are given per 1000' of wire. You'll need a very accurate meter to tell the difference between #12 and #14 on a 50' or 100' cord.

http://www.powerstream.com/Wire_Size.htm

#### Bud9051

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I just Googled "ohms per foot for electrical wire" and got:
14 ga = 2.5 ohms per 1000' and 12 ga was 1.6 ohms for the same 1000'

Very small numbers if trying to measure 50 or 100 feet of wire. That would require a really good meter and still not really accurate.

lets see what the electrical pros suggest.

Bud

#### joed

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You can not determine gauge by measuring ohms. It would require test equipment of scientific quality.

You need to try and find it on the cord. Almost all cords have it imprinted into the casing. It might be small but it should be there.

#### Oso954

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If you look here, you will see the ohms/1000 ft varies by temperature.
http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html

I’d look again for the printed info on the jacket. Note that it is often just stamped into the jacket (no ink).

Why do you believe that they are 12 or 14 awg ? The most likely gauge for a typical homeowner outdoor extension cord would be 16 awg.

The ultimate method for finding the wire gauge is to cut one of the cord caps off off and measure the wire diameter. Then install a new cord cap.

#### mpoulton

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Measuring very low resistances is difficult. Like, "a difficult problem for engineers to solve" level of difficult. To do it on an extension cord would require a current source to drive several amps (the more the better, so let's say 10A) through the cord, a current meter to measure that current accurately, plus a separate very accurate voltmeter to measure the voltage drop across the cord. The fun part is that your voltmeter needs to be connected to the ends of the cord SEPARATELY from the current source. This is called a "Kelvin connection" or "Kelvin leads" (named after the scientist who figured out that you have to do it this way). This eliminates the effect of contact resistance, which would otherwise make your measurements totally useless. It's easy to get a Kelvin connection on the male end of the cord, but the female end will be a challenge.

Not worth it to figure out cord gauge. A fun experiment to see if you can come up with a test apparatus that would even give you a useful result, though.

#### Bud9051

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Not sure what you have for a meter but here is a thought. You want to know if they are 12 or 14 ga so compare whatever you read to a known power cord. That way it doesn't matter what the exact readings is, just whether it is equal, higher, or lower. Ballpark solution.

Bud

Nealtw

#### joed

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That won't work. You are talking a 1 ohm difference. only scientific equipment can measure that accurately.

#### Bud9051

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That's why I asked what he has for a meter. Some meters will read down to tenths of an ohm and he really doesn't need an accurate reading just the ability to compare a known power cord from the ones he has. Not perfect but not worth seeking a scientific reading.

Bud

#### Gregsoldtruck79

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While using the chart I linked to above, then in theory the total R for each insulated conductor in an 100 ft. long #14 gauge extension cord is as follows in my sketch.

But as already stated here, these calculations would have to be done in a test lab setting, with all the test parameters set up in a controlled environment to get a sound and proven result.

And all while using various ampere loads on the cord, while in various ambient temperature settings. I see now, this topic is WAY over my pay grade here....

#### Bud9051

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Hi Greg, the exact measurement can be rendered irrelevant by comparing the power cords in question against known power cords. Since both would be at the same temperature that variable is eliminated and since all the op wants to know is whether his cords are 14 or 12, IF he has a sufficiently precise meter the comparison could give him an answer.

Bud

#### joed

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The connection of your meter to the cord will probably be a higher resistance than the cord you are measuring.

#### AllanJ

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Consumer grade meters, thermometers, etc. that measure to a tenth of a degree, volt, ohm, etc. are somewhat of a joke. THey tend to be off by a few whole volts or degrees, etc. and not uniformly across the range.

Acceptable for an amateur or even a professional electrician for typical wiring jobs and troubleshooting but not for trying to figure out the gauge of wire in a cable.

In high school science classes I learned about "uncertainty." For example a typical voltage measurement might be 12 volts plus or minuts a quarter volt. Delving into details, when adding or subtracting two quantities the uncertainty of the result is the sum of the absolute values of the uncertainties for example if we subtract 5 volts +-1/8 volts from 12 volts +-1/4 volt we get 7 volts +-3/8 volts.

Getting out of the world of minutiae back to basics, even you willl agree that 117.3 volts plus or minus 2.1 volts sounds like a joke.

Oso954

#### Gregsoldtruck79

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Hi Greg, the exact measurement can be rendered irrelevant by comparing the power cords in question against known power cords. Since both would be at the same temperature that variable is eliminated and since all the op wants to know is whether his cords are 14 or 12, IF he has a sufficiently precise meter the comparison could give him an answer.

Bud

Just for reference and I doubt if todays extension cords vary by much. As most all of them are MIC and they put the least jacket thickness on them allowed I bet.

I just measured the outside diameter of three of my factory extension cords. All of my cords still have the manufacturers stamp on the cord showing what size conductors it has in them ( 3 wires each in them)

16 gauge conductor cord measures .300 in. O.D.

14 gauge " ......................... .355 in. O.D.

12 gauge " " ' .566 in. O.D.

#### viper

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What is going to be relatively precise if you really want to chase the rabbit, is DC voltage drop. I recommend to simply jumper one end of the cord so you can double the effective length, which will increase test accuracy.

Use a DC voltage source at one side, and use the returned DC voltage to power a DC resistive load. This can be a lightbulb or whatever. Use something that is within the margins of your ampacity, so lets say 10-15A. couple of 55w DC bulbs, 110W/12V 9.16A. You would need to record the applied voltage while under load, the returned voltage, and the current. With that information, you can determine the resistance in the wire, which will give you the info you seek.

DC volts is the most accurate value for meters to read but regardless, it is relative, just use the same meter for all tests.

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