From 314.17 (C) of 2014 NEC.....
Where nonmetallic sheathed cable or multi-conductor Type UF cable is used, the sheath shall extend not less than 6 mm (1/4 in.) inside the box and beyond any cable clamp. In all instances, all permitted wiring methods shall be secured to the boxes.
Last edited by HotLine1; 11/17/14 11:04 AM. Reason: Corrected copy booboo