National Electrical Code Tips: Article 725, Class 1, Class 2, and Class 3 Circuits. Part 2.

1. Part II of Article 725 provides the requirements for Class 1 circuits. However, Part III provides the requirements for both Class 2 and Class 3 circuits. Why is Class 1 by itself, and the other two are together? It has to do with the power limitations. These make the requirements for Class 2 and Class 3 very similar to each other, but they make the requirements for Class 1 enough different from the other two that it Class 1 needs to be addressed separately.
   
2. A Class 1 power-limited circuit is one supplied by a source with a rated output of not more than 30V and 1kVA [725.41(A)].
   
3. A Class 1 remote-control or signaling circuit is a circuit that's used for remote-control or signaling and operates at 600V or less [725.41(B)].
   
4. The requirements for Class 1 power sources are in 725.41(A).
   
   
   
   
   
5. If the conductors are 14AWG or larger, provide overcurrent protection the normal way; except you don't apply the ampacity adjustment and correction factors of 310.15 to the ampacity calculation [725.43].
   
6. Overcurrent protection can't exceed 7A for 18AWG conductors or 10A for 16AWG conductors [725.43]. Except as permitted by other Articles.
   
7. Install OCPDs at the point where the conductors receive their supply [725.45(A)]. This is generally true of all circuits and because of that the OCPD defines the circuit.
   
8. You can use branch and feeder taps, if you follow specific rules pertaining to them [725.45(B) and (C)].
   
9. Install Class 1 circuits using the appropriate Articles from Chapter 3 [725.46].
   
10. You can install Class 1 conductors with other circuits, if you meet the applicable requirements specified in 725.48.