I was walking through a house during the middle of construction and came across what appears to be a recpticle attached to a pvc pipe that seems to pass a low voltage wire. Also connected to the receptacle was a 14 gauge wire.
That appears to be a central vacuum system. The LV wire is to turn the vacuum on via a relay. Hard to tell from the picture if the end of the wire has simply been tucked into the pipe awaiting the final cover-plate install that it will be pulled out and wired to (correct) or if some genius ran the wire inside the vacuum tubing (incorrect.) I would bet on the correct case, though.
The 14 gauge wire would provide AC power for a beater-brush or similar accessory on the vacuum-hose.