I was digging the holes for some crepe myrtle saplings and I sliced into a wire with one unlucky shovel stroke. They do not seem to be carrying any voltage, but I haven't hooked my multi-meter up to it yet. I've called 811 several times in the past, and nothing has ever been marked out anywhere near this side of the yard. The wires themselves are 2 red, 1 white, solid copper core, maybe 20 gauge (slightly heavier than say speaker wire). They are buried ~4 inches below the surface with no conduit or protection. They are a few inches away from the sprinkler PVC pipe, running roughly parallel to it and the driveway, towards the street away from the front corner of the garage where the sprinkler control system is.
The sprinkler control box still has power and it can still turn on the sprinklers. I did a short test run of the zone that the wires are running through, and they had normal pressure (after pushing out all the air that accumulated over the winter).
I switched to a hand-spade and started tracing the wire route through the garden. The wire seems to be getting deeper as it approaches the house, but I lost it in the twilight under a tree root.
Does anyone have a premonition about what these wires could be? If I do test the wire and find it dead, is there any danger in yanking the severed wire out of the ground to trace it? Is it worth calling 811 again and waiting to see if any of the utilities own up to it?
Additional Information (in response to comments):
The sprinkler system came with the house, so it's builder grade. I'm tempted to believe the theory that they are trace wires for the sprinkler PVC, except that I've gleefully hacked through the PVC on the other side of the yard with no sign of wires. I have not yet disassembled the box wiring to see if a white and two red wires connect to it, although the sprinkler panel and manual don't mention any fancy features like rain sensors.
We have no exterior electrics. No lights or fountains or anything. The only outdoor outlets we have are built into the base of the house. The nearest one to these wires is on the other side of the driveway.
I agree that it is unlikely it's any part of a utility. The location is haphazard and I'm pretty sure there's a building code for underground current carrying wires to have conduit. I can see the builders skimping on that, but not a utility.