What is the difference between CL2 and CL3?
CL2 is the designation for Class 2 Circuit wire and CL3 is the designation for Class 3 Circuit wire. Both are regulated under NEC Article 725. They are both used for remote-control, signaling, and power-limited circuits. In plain English that means that CL2 and CL3 are types of multi-purpose wire used for things like security systems, speaker wire, intercom systems, nurse call buttons, and more.
The difference between the two is that CL2 is rated for up to 150 volts while CL3 is rated for up to 300 volts. (NEC 725.71 F) According to NEC 725.2, CL2 offers some protection from electric shock while CL3 offers a bit more because it is rated to carry more voltage.
CL3 may be used in place of CL2, but not the other way around.