Determining Unknown AWG

You have used a good methodology and it would seem that you are on the right track.

The cautionary note that I would toss in here is that there are at least four different methods of describing wire gauge and the descriptions seem intentionally similar to create confusion.

One (as you have described) uses the cross sectional area of the conductor material and is what I would use in engineering calculations.

Another used the wire diameter to describe the "gauge". In metric this can be expresed in mm and sometimes called "mils".

And yet another uses the conductor circumference in "mils" (That's the imperial mils as in thouandths of an inch, not the metric system.) and calls this measure "circular mils".

Another talks of the cross sectional area of the conductor in metric "square mils".

I've always found it useful to describe the wire (stranded or solid) by describing the cross sectional area, then describing the construction detail using conductor count and strand diameter.

Beware the salesmen and ALWAYS check the calculations.

This seems like a very accurate method for calculating the cross-section of a few strands.

If you are just trying to identify the AWG of the conductor, it might be faster and more accurate to weigh a known length of the bare conductors and compare to a weight per length table. Sure, if you don't have an accurate scale, but have an accurate micrometer, then your method is probably better.

Depending on the type of stranding, there is such a significant difference in the diameters of the various gauges that we trust our sizing gauge - made for wire just like the common bolt gauges.

You could also measure the resistance of a length of wire. I believe resistivity of different wire gauges is given in electrical handbooks. This would require a very sensitive instrument, maybe a wheatstone bridge.

Thanks to all of you that responded to my question. I can't say that there is any best answer among those responses. You each basically substantiated my assumptions and also offered some other options for me to consider. All is appreciated . . .

What you are depending on, though, is the accuracy of your measurements. The risk of using a conventional micrometer is that your use assumes the wire is in fact round. It may not be.

In a machine shop, one would use a 3-point method (two anvils at 120 degrees and a micrometer head splitting the angle) to measure at several places around the circumference of the wire.

However, the inaccuracy of your method is probably not great enough to throw you off even by one gauge of wire.

Sounds very accurate. So, let's say I had a 19-strand conductor composed of 40 AWG strands (of course, I wouldn't know this upfront). Then, using your method, I would be measuring a strand diameter of 0.00314 in. from 3 equidistant points around the circumference of the wire. I'm not familiar with measuring instruments you described, but I'm pretty sure I don't have those in my tool-box.

I'll take your third paragraph as a conditional endorsement of my shade-tree method.

I assume that because you posted in electrical you are using the wire as a conductor. There is a school of thought that the electrons flow around the outside of a conductor and so multiple strands may carry more current than a single conductor per area as there is a greater circumference/surface area. Physical strength such as tension and multiple bending can be a consideration that reflects on choice of wire. Are the conductors steel, aluminium or copper? Is the wire to be buried or embedded in concrete? How long is the run?

All of these affect the current carrying capacity of the wire.

I apologise if i'm trying to teach grandmother to suck eggs but i know most electricians can tell a wire gauge just by looking at it, so i assume that you know/have been told what size wire you need and have some of unknown gauge available to you. Hence your desire to measure it. I am just trying to point out that the size given to you may not be correct, depending on your particular circumstance.

So reading between the lines, my multi-strand conductor should actually be capable of a slightly higher current than that of a solid wire of equivalent gauge. That gives me a built-in safety factor.

I'm not trying to determine the suitability of a particular conductor - I'm merely trying to document the gauge of conductors used in a current device (don't ask why).

So reading between the lines, my multi-strand conductor should actually be capable of a slightly higher current than that of a solid wire of equivalent gauge. That gives me a built-in safety factor.Correct.See post #1 re gauges. There is the Birmingham wire gauge, American wire gauge ( this is the one you stated as AWG ) and the Standard wire gauge, all of them different. I trust you know that it is definately AWG that you require. I only ask this because i do not know which part of the world you are in. Most of the world now uses the metric system.Jim

..the skin effect (conduction near surface of wire) is meaningfull at high frequencies. At 50Hz /60Hz difference will be unmeasurable.

On the other hand, solid wire can dissipate heat better (to insulation), than stranded cable. Air between wires in stranded cable act as thermal insulation. So equivalent (from the point of view of loadability [Amperes]) single wire will have a little smaller gauge. Have a look at catalog of good cable maker. They usually write about that. And about importance of surrounding: air? ground? other cables? On the spool(loadability must be reduced to ca 1/2)

Plz check this URL

http://www.ehow.com/how_5839201_convert-wire-gauge-inch.html#ixzz24OcznHkS

I appreciate your response, however it has two problems:

1. It derives diameter from gauge, I can do that with a good table and it's the opposite of what I asked (gauge from multiples of the same diameter).

2. It only deals with single-strand wire - I need the gauge of multi-strand wire.

p.s. Off-topic a bit, but I generally shy away from Ehow. I find the answers to usually be too simplistic and non-specific. This one seems to be the exception - if only it fit my situation.