# How to determine wire gauge.

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

1. ### Tibur WaltsonGuest

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
wire gauge when they look the same?

TIA, Tibur

2. ### Michael A. TerrellGuest

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 MastaGuest

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
www.daqarta.com

4. ### Bill VajkGuest

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

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
comparison.

http://www.techfest.com/networking/cabling/gage.htm

As you can see the larger the number the smaller the wire.

5. ### Bill VajkGuest

Modern appliances sometimes use small wire with a thick
insulation, and he's slavaging the stuff out of
everywhere.

6. ### Michael A. TerrellGuest

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. ### Tibur WaltsonGuest

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?

Tibur

8. ### John FieldsGuest

---
The problem is you're a fucking idiot.

_Measure_ the diameter of the wire, then use a copper wire table to find
the gauge.

http://www.mwswire.com/barecu1.htm

9. ### Tibur WaltsonGuest

Here, take a look at some wires I scanned.

http://tinyurl.com/2erh8

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.

Tibur

10. ### Bill VajkGuest

Let's get the units right. 2.2cm = 1 inch.
How about a guess of copper vs. aluminum?

11. ### Robert C MonsenGuest

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(-------------)
(1.26096^(G-1))

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)
--------------------------------------------------
83690
rho at 20C, l in feet, T in C.

Regards,
Bob Monsen

12. ### Bill VajkGuest

I swear I pressed the ~, sorry.

13. ### Tibur WaltsonGuest

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 the 15 AWG is found to be an inferior conductor, I will throw them
out. Or has Robert and Bill already provided the answer. . . ?
Tibur

14. ### Bill VajkGuest

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

http://www.ibiblio.org/obp/electricCircuits/Ref/REF_3.html

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

15. ### Steve DunbarGuest

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. ### Tibur WaltsonGuest

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.

Tibur

17. ### Tibur WaltsonGuest

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, mswire.com/barecu1 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