Still More on Litz Wire

Bob Bruhns
Sun, 26 Apr 1998 12:48:25 -0400

I neglected to mention the New England Electric Wire Corp. URL:

and their informative technical information URL:

These URLs are referenced at the end of Jim Hawkins' excellent
NSS page at:

"Skin depth" means the depth at which current drops to
approximately 37% of the surface value.  In copper at 21.4 KHz
this is about 0.0178 inches (0.452 mm).  Skin depth is an inverse
function of the square root of frequency; in copper at 188 KHz it
is about 0.006 inch (0.152 mm).

  The equation is 2.6*K/SQRT(freq, MHz), giving skin depth in
mils (thousandths of an inch); K = 1 for copper.  Surprisingly,
at 60 Hz skin depth in copper is only about 0.335 inch (8.53 mm),
and at 50 Hz it is about 0.368 inch (9.34 mm)!

  If the conductor has magnetic permeability, skin depth is even
less than that.

  Bob Bruhns, WA3WDR,