Ask A Scientist© Environmental Earth Science Archive

status       student
age          20s
Question -   How do coaxial cable work?

Coaxial cables are made of four layers.  At the inside is a metal wire.
Insulation, perhaps rubber or plastic, is around the wire.  At this level
you have just an ordinary electrical wire.  What makes it coaxial is the
next layer:  a metal layer around the insulation.  Then a layer of
insulation goes around the outer metal layer.

A coaxial cable works just like two wires, except one is "inside" the other.
Current flows from the power source through one metal layer, flows through
the equipment at the other end, and then flows back to the power source
through the second metal layer.

The purpose of coaxial cables is to eliminate magnetic effects.  Any single
wire with current flowing through it produces a magnetic field circling
around the wire.  This field can then affect other wires.  In a coaxial
cable, the current of the inside and outside layers flow in opposite
directions.  Their magnetic fields are in opposite directions.  The magnetic
field from the outside wire cancels the magnetic field from the inside wire.
Although there is magnetic field between the metal layers, there is no field
outside the cable.  Also, a coaxial cable is not affected by magnetic fields
from other wires.

One benefit of this relates to computers.  A computer disk is magnetic.
Magnetic fields can accidentally clear a computer disk.  Coaxial cables are
much safer near disks.  Another benefit concerns very high voltage cables.
Because one conductor surrounds the other, you cannot touch both at the same
time.  It is a way to reduce chances of electrocution.

Kenneth Mellendorf
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