Article 725 is one of the worst examples of law writing in existence. It is complete garbage. In the older versions, about 1996, it defined the three clases in confusing terms of VA [volt-amperages], but I believe that in later versions, the idiot code panel simply deleted these definitions. Thus, the entire article is now about something that is undefined.
In other words, an intelligent person can read the entire article and not know what it is talking about.
Class I devices are those which say they are Class 1 devices. [I think an example would be fire alarms.]
Class 2 devices are those that state they are Class 2 devices. Typical is a wall wart.
Class 3 is of doubtful existence. That's because I can't think of any thing which would dare to call itself "Class 3". But it doesn't seem to matter since Class 3 seems to be treated the same as Class 2 anyway.
The main importance of this article is to slightly relax certain rules since these devices or systems are presumed to have lower risk of fire and/or shock. Thus you can have more wires in a fire alarm conduit since they tend to be low amperage. And the other classes can be treated like telephone or data lines. But don't quote me on this.
~Peter
