Article 725 Class 1, Class 2, and Class 3 Remote- Control, Signaling, and Power-Limited Circuits
Informational Note: The circuits described herein are characterized by usage and electrical power limitations that differentiate them from electric light and power circuits; therefore, alternative requirements to those of Chapters 1 through 4 are given with regard to minimum wire sizes, ampacity adjustment and correction factors, overcurrent protection, insulation requirements, and wiring methods and materials.
Cable Bundle. A group of cables that are tied together or in contact with one another in a closely packed configuration for at least 1.0 m (40 in.).
Informational Note: Random or loose installation of individual cables can result in less heating. Combing of the cables can result in less heat dissipation and more signal cross talk between cables.
Exception No. 1: Class 2 and Class 3 cables selected in accordance with Table 725.154 and installed in accordance with 725.135(B) and 300.22(B), Exception shall be permitted to be installed in ducts specifically fabricated for environmental air.
Exception No. 2: Class 2 and Class 3 cables selected in accordance with Table 725.154 and installed in accordance with 725.135(C) shall be permitted to be installed in other spaces used for environmental air (plenums).
Exception: Conductors with green insulation shall be permitted to be used as ungrounded signal conductors for Types CL3P, CL2P, CL3R, CL2R, CL3, CL2, CL3X, CL2X, and substitute cables installed in accordance with 725.154(A).
Informational Note: Paint, plaster, cleaners, abrasives, corrosive residues, or other contaminants can result in an undetermined alteration of Class 1, Class 2, Class 3, and PLTC cable properties.
To comply with the 1000 volt-ampere limitation of 725.41(A), the maximum output (VAmax) of power sources other than transformers shall be limited to 2500 volt-amperes, and the product of the maximum current (Imax) and maximum voltage (Vmax) shall not exceed 10,000 volt-amperes. These ratings shall be determined with any overcurrent-protective device bypassed.
VAmax is the maximum volt-ampere output after one minute of operation regardless of load and with overcurrent protection bypassed, if used. Current-limiting impedance shall not be bypassed when determining VAmax.
Imax is the maximum output current under any noncapacitive load, including short circuit, and with overcurrent protection bypassed, if used. Current-limiting impedance should not be bypassed when determining Imax. Where a current-limiting impedance, listed for the purpose or as part of a listed product, is used in combination with a stored energy source, for example, storage battery, to limit the output current, Imax limits apply after 5 seconds.
Vmax is the maximum output voltage regardless of load with rated input applied.
Exception: Where other articles of this Code permit or require other overcurrent protection.
Exception No. 2: Methods permitted or required by other articles of this Code shall apply to installations of Class 1 circuits.
- The power-supply or Class 1 circuit conductors are in a metal-enclosed cable or Type UF cable.
- The conductors are permanently separated from the power-supply conductors by a continuous firmly fixed nonconductor, such as flexible tubing, in addition to the insulation on the wire.
- The conductors are permanently and effectively separated from the power supply conductors and securely fastened to racks, insulators, or other approved supports.