Bare copper drain wire

Except the outer jacket that protects against physical damage a cable also has a shielding for protection against external signal interferences. These interferences may corrupt data transfer or create unwanted noise in an audio signal. Different types of shielding are used, as they differ in their specific advantage in protecting signal frequencies.

The drain wire is a part of a shield within a cable that reduces the resistance from any point on the shield to ground. A drain wire carries extraneous electrical noise to ground and away from the circuit or system.