BNC cables are commonly used to transmit electrical signals. In particular, they are used to couple signals into an oscilloscope. BNC cables carry the signal along a wire on the axis of the cable. This wire is surrounded with an insulator, which is wrapped with a braided shield. Normally, this shield is connected to ground via the BNC connector at the ends of the cable, although the connectors may allow the shield to "float" to whatever voltage it wishes. The shield is very helpful in isolating the inner conductor from stray electromagnetic fields, which would produce noise.
Updated 6/17/99 by Peter N. Saeta .