The copies of the entries I've seen said,"Detailed to work on North Carolina R.R. April 6, 1863."
In April 1863, the 17th TN had recently fought at Stones River (12/31/62) in Murfreesboro and were on their way to Chattanooga for the Battle of Chickamauga(Sept 19-20, 1863).
Since the Nashville & Chattanooga Railroad went through Murfreesboro from Nashville, toward Chattanooga, why would soldiers be detailed to work in North Carolina, several hundred miles away?
By April of 1863, they were probably in, or near, Franklin County, TN where the 17th TN was from.A lot of that area is mountains and requires special pushers (train engines) to help push the train up the mountain.I suspect that those who were detailed to work on the railroad, resumed their civilian jobs as pusher engineers on the Nashville & Chattanooga Railroad.