Tetrix wires come with tinned ends which is a huge no-no when using screw terminals. After tightening the solder will creep and a few days later the wire will be loose. Bare wire is considerably better but better still are ferrules. Since we started using them the only loose wire we've had has been self-inflicted.
This is the ferrule set we bought:
http://www.automationdirect.com/adc/...Tools/BM-80418
The crimping tool is of medium quality--perfectly adequate for what we do but there are much nicer ones.
On the same topic, the Tetrix power switches come with connectors crimped onto tinned wires--this is absolutely the wrong way to get a reliable connection. Crimp on connectors should only be used on bare wire.