shielding - Does the "drain" wire in a microphone audio cable serve any purpose the shield does not?

I'm helping a friend with an audio installation, and he asked about the requirements for the microphone cable:

"Wiring Requirements: 2 Conductor shielded cable, 22 gauge with a 24 gauge drain wire.

The requirements imply that a 24 gauge drain wire is a necessity, but if the cable is properly shielded, is the drain wire a necessity? Other than providing some additional strength to the cable and/or an easy way to connect to and solder to the grounded shield, does it serve some additional purpose?

It is intended for an unbalanced electret microphone; I'm interested in other uses if not applicable here.

Answer

I think I've only seen drain wires in foil-shielded cables (but I could be wrong...). It is not possible to make a secure connection to the foil shield, so the drain wire is the only way to make the shield connection.

A drain wire is not required with a braid shield, as you can unbraid a bit of the shield, and twist the strands to make a "wire" that you can use to make a secure connection.