300.22 discusses wiring methods permitted in ducts. K & T isn't one of the permitted methods.
That aside, this duct was certainly made after the wire was in place, and well after the building was first put up. The resulting violation is probably due to ignorance on the part of the installer.
The short version: wiring inside ducts has to be in a metal conduit of some sort, or be miner-insulated cable.
I have often seen wires pass through ducts- form side to side- but this is the first time I've seen the wires running lengthwise within the duct.
I am told, by my friends in the HVAC community, that such "made" ducts have prooven to be rather poor ducts, and that the practice of making a duct by closing off a joist bay is abvoided by better contractors. It may (I don't really know) also violate some of the newer energy codes.
