We do 6 digits. First three are room number, last three are wire number.

First of the 3 digits is the floor so if Kitchen is on the first floor its number might be 101. If the speaker cable is wire 009 then the speaker wire label will be 101-009.

Room numbers are usually decided by the architect or we just number them randomly on the print. Wire numbers are randomly created as wires are added to the print.