No, that is 6 gauge NM-B (also known as Romex cable). It has to be used at the 60 degree C temperature rating level, which for 6 gauge is only rated for up to 55 A circuits. You can't use it for a 60A circuit that runs at 48A continuous. But it's really no problem to use that properly for a 50A circuit. Here's the rating table to see this:
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com
