# secondary wire length

```Hi all,

I just saw a formula on the web for calculating the length of wire would on
a secondary coil-form:

[pi]DNH
L= ---------  where,
12

L=length of wire in feet
D=outside diameter of coil form
N=number of turns per inch
H=height of coil winding itself

Basically, this formula states that "the circumference of a single turn,
multiplied by the number of turns, will give the length of the wire."

What I'm thinking is, that a single turn doesn't meet its beginning, but
overlaps itself, and so, is slightly (*very slightly* in a close-wound coil
;) longer than what the calculation yeilds for a single turn.

In a close-wound coil it's probably no big deal, and truthfully, I don't
calculate wire-length anyway (unless I'm researching).

But if a person were to wind a space-wound coil the error would be
significant, and I'm thinking that I'd use a different formula for
calculating wire length. I believe this one would be more accurate in all
cases:

HN(sqrt(([pi]D)^2+p^2))
L =  -------------------------  where:
12

L=length of wire in feet
p=distance (pitch) between turns *center to center*
D=outside diameter of coil form
N=number of turns per inch
H=height of coil winding itself

Basically, this is the same as the first formula, except that it gives a
more accurate length of wire per turn.

The way I'm thinking of it is that the actual circumference of a turn would
equal the length of one leg of a right-triangle. The *center to center*
distance between the wires of a single turn would equal the other leg of
the right triangle (This would be a very short leg ;) The hypoteneuse of
that right triangle would then be the actual length of a single turn.
Turns-per-inch (if spaced) would have to be counted, but height of the
actual winding would still be the same as in the original calculation.

I know it's picky, but it might help someone someday :)

Thanks,
Dan
ntesla-at-ntesla.csd.sc.edu

```