The move is retroactive to July 12.
Nationals manager Matt Williams said Carpenter was poised to pitch last weekend against Baltimore but didn't feel good enough to enter the game.
Carpenter tested the shoulder Thursday and was not at 100 percent, leaving Williams little choice but to put the reliever on the DL.
"Rather than play short -- he's already a few days into it anyway -- we just put him on the DL," Williams said. "We want to make sure he's ready to go when he gets back."
Carpenter has a 1.50 ERA in eight games out of the bullpen this season. He was acquired from the New York Yankees on June 11.
Washington filled the void by recalling left-hander Sanny Solis from Double-A Harrisburg. This will be his third stint with the Nationals this season.
Solis is 1-0 with a 4.50 ERA in six games with Washington, all of them in relief.