If your house was built in the 1960’s or 1970’s there is a good chance your house may be wired with aluminum wire. Aluminum wire can cause fires especially when connecting old aluminum wire with new copper wire. Never use a wire nut to connect aluminum and copper wire. The two metals expand and contract at different rates so the connection can become loose, arc, and eventually start a fire. Don’t worry, there is a safe way to connect your old aluminum wire to a new copper fixture or other copper wire. Its called Alumiconn and its a brilliant little device that takes the danger out of making aluminum to copper splices.
To be safe, the slotted screws that hold the wire in place need to be torqued to the manufacturers specified torque of 10 or 15 In/lbs for #10 and #12 wire respectively.