Really depends on what you need to know of "the basics", electrical theory, or practical installations, code, what exactly. There is a great deal of information, that really should be learned in order, otherwise, you can run into something that will make no sense if something was skipped.
Ugly's Reference came to mind, has a bit of the most used concepts, but does not really explain too much as by the time you need one of these there is an understanding and just reference is needed.
A very good all around book with a brief description of theory, formulas, practical installation, etc. is the
American Electricians Handbook.