(2) To the power-supply conductors only, where the Class 1 circuit conductors do not carry continuous loads in excess of 10 percent of the ampacity of each conductor and where the number of power- supply conductors is more than three
(C) Class 1 Circuit Conductors in Cable Trays. Where Class 1 circuit conductors are installed in cable trays, they shall comply with the provisions of 392.9 through
392.11.
725.52 Circuits Extending Beyond One Building. Class
1 circuits that extend aerially beyond one building shall
also meet the requirements of Article 225.
HI. Class 2 and Class 3 Circuits
725.121 Power Sources for Class 2 and Class 3 Circuits.
Figure 725.121 Class 2 and Class 3 Circuits.
Exception No. 2 to (3): Limited power circuits of listed equipment where these circuits have energy levels rated at or below the limits established in Chapter 9, Table
11(A) and Table 11(B).
FPN: Examples of other listed equipment are as follows:
(1) A circuit card listed for use as a Class 2 or Class 3 power source where used as part of a listed assembly (2) A current-limiting impedance, listed for the purpose, or part of a listed product, used in conjunction with a non-power-limited transformer or a stored energy source, for example, storage battery, to limit
the output current
(3) A thermocouple
(4) Limited voltage/current or limited impedance secondary communications circuits of listed industrial control equipment
(4) Listed information technology (computer)
equipment limited-power circuits.
FPN: One way to determine applicable requirements for listing of information technology (computer) equipment is to refer to UL 60950-1-2003, Standard for
Safety of Information Technology Equipment. Typically such circuits are used to interconnect information technology equipment for the purpose of exchanging information (data).
(5) A dry cell battery shall be considered an inherently limited Class 2 power source, provided the voltage is
30 volts or less and the capacity is equal to or less than that available from series connected No. 6 carbon zinc cells.
(B) Interconnection of Power Sources. Class 2 or Class
3 power sources shall not have the output connections
paralleled or otherwise interconnected unless listed for
such interconnection.
725.124 Circuit Marking. The equipment supplying the circuits shall be durably marked where plainly visible to indicate each circuit that is a Class 2 or Class 3 circuit.
725.127 Wiring Methods on Supply Side of the Class 2 or Class 3 Power Source. Conductors and equipment on the supply side of the power source shall be installed in accordance with the appropriate requirements of Chapters 1 through 4. Transformers or other devices supplied from electric light or power circuits shall be protected by an overcurrent device rated not over 20 amperes.
Exception: The input leads of a transformer or other power source supplying Class 2 and Class 3 circuits shall be permitted to be smaller than 14 AWG, but not smaller than 18 AWG if they are not over 12 in. (305 mm) long and if they have insulation that complies with
725.49(B).