[rohrmann]

When using any screw type connector with stranded wire, copper or aluminum (use No-Ox with aluminum), you should tighten the screw and wiggle the wire as you tighten, then wiggle again and, again tighten. If you just screw down on the wire without doing this, as the connection goes through the heat and cool cycles, the connection will become loose as the strands move around. If you use the above method, you will rarely have any problems, assuming the connector is rated for the amps that will be expected. Solid wire, as is in Romex, is does not need the wiggle to make screw connections. Also, the screws normally don't loosen from vibration, so it is not wise to use any thread locker due to the softer metal used in electrical connectors (you may need to take it apart some day). The connectors have to be a similar metal compared to copper so when the wire and connector naturally warm up with load, and then cool down when unloaded, they expand and shrink at the same rate.