Software is almost never free! There may be certain functions disabled such as saving or saving in other formats other then the vendors. So if you are doing anything important and you don't want to loose your hard work. Make sure you fully understand what your getting and make some test drawings first to go through the functionality of the CAD software.
There are many programs out their that can be used for most basic designs for the average person. Here are some of the programs that might fit your CAD / CAM needs and electrical autocad type applications. Autocad and solidworks are great programs but are expensive for most people who use it occasionally.
If you have any other CAD suggestions for software other then what is listed here please send your suggestion and I will consider adding
A light version of their commercial software. Parametric & feature based 3D modeler, which is fairly easy to use. 2D layout & detailing is fully associative with the 3D model. Shelling & booleans are not offered in this light version, but you are able to "Save" your models. Assembly is limited to 25 components
A well known Program used for 3D modelling, Rhino provides the tools to accurately model your designs for any application. You can "Save" your models 25 times so it is not free forever but a nice piece of software to try anyway.