On 27 Apr 99, at 14:36, Don Riggs wrote:

> Those current-carrying wires are enclosed in close proximity in a cord, and
> the opposite direction of current flow cancels the external magnetic field
> to a great extent.  Example:  A clamp-on type meter cannot reliably measure
> the current through a cord; the two current- carrying conductors must be
> separated and the clamp placed over one of them to measure current.
>
> <snip>
>
> That does not seem to apply to digital signal systems to any great degree.  I
> have seen installations where hundreds of feet of Cat-5 cabling for 10 baseT
> and 10/100  systems were in close proximity, with no apparent ill effects.

  Reacll that Cat-5 is unshielded *twisted pair*.  Exactly the same
phenomenon limits external magnetic field from these cables as in the power
cords alluded to above.
David G

         The PCBUILD web site always needs good submissions.  If
          you would like to contribute to the website, send any
               hardware tech tips or hardware reviews to:
                           [log in to unmask]