Here are two more sites - these are not NEC but have to do with other electrical instruction....motor controls, PLCs, VFD, transformers, etc.....both of these sites are free
Cutler Hammer Univeristy
This site has a series of intereactive courses that teach basic electricity, fundamentals of DC and AC circuits, transformers, circuit breakers, panelboards, motors, and PLC's. There are 27 modules. They can be purchased in a 3-ring binder for $350, or be taken on line at no cost. This site is highly recommended, especially for those who do not have a strong electrical background.
2 - Siemens has a similar interactive online course... www.sea.siemens.com/catmain.htm
(for some reason Siemens is sometimes hard to 'connect' to...you get errors messages, and at other times you just get right onto the site.....I'm working from memory here - I believe at the top of the page is a Tab titled Training...or Education...anyway, click the tab and it moves you to the training section....register for free and all the modules are available.