DIYbanter - View Single Post - Any way to "measure" wire gauge in power cord?

blueman

(Dave Martindale) writes:

blueman writes:
dpb writes:

blueman wrote:

12 AWG -- ~0.081"
14 AWG -- ~0.064"

So, 12 is a little over 1/16", 14 is about 1/16" diameter. Enough
difference if the connection at either end is visible to tell easily.

Do these numbers apply to stranded too? (I believe the power cord is stranded)

Close, but not exactly. Stranded wire of a particular gauge will have
the same amount of wire cross-section area to carry current as solid
wire of the same gauge. Because there's some air spaces between
strands when they are packed as tightly as possible, the overall
diameter of the bundle will be slightly larger for the stranded wire,
but only by about 10%.

You can calculate the size increase yourself fairly easily:

Perhaps the simplest stranded wire that's still well-packed has 7
strands, one in the centre and 6 around it. This gives hexagonal
packing, with the centre strand touching all 6 outer strands, and each
outer strand touching two neighbours as well as the centre strand. If
the diameter of one strand is 1 unit, the diameter of the whole bundle
(measured in the direction that gives the largest measurement) is 3.
With 7 strands, the wire has 7 times the cross-sectional area of one
strand, and will carry 7 times the current. A *solid* wire with the
same current capacity and resistance would be sqrt(7) = 2.645 units in
diameter, while the 7-strand wire is 3 units in diameter - about 13%
larger.

(On the other hand, if you measure across the "flats" of the stranded
wire, with the caliper jaws touching two wires each, the measured
diameter is only 2.732 units, or only 3% larger than a solid wire of the
same metal cross section. So it matters how you measure).

In a wire with many more strands (e.g. welding cable), the outside
becomes rounder, so the diameter measurement doesn't vary significantly.
And the "extra" diameter for stranded approaches the ratio of the area
of a hexagon to a circle inscribed in it, which is sqrt(12)/PI, or about
1.103. In other words, the many-strand cable is 10% larger than the
equivalent solid wire.

Dave

Cool! Thanks for the detailed explanation.