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A Code Guide reader recently sent a list of various types of instrumentation circuits and asked how the circuits should be classified. He wanted to know if the various circuit types were Class 1, Class 2, Class 3, or some other classification covered by the NEC, or if the NEC covered the circuits at all. The classification of instrumentation circuits and other remote control, signaling, and power limited circuits is a common source of problems for users of the NEC. This Article will attempt to clarify some of the confusion that surrounds Article 725. We should first establish what Article 725 is about and what it is not about.

For instance, a common misconception about Article 725 is that it allows CL2 or similar 'thermostat wire' or 'bell wire' to be used on 'low voltage' circuits. (In this context, 'low voltage' is usually taken to mean less than 50 V or less than 100 V. This definition of low voltage is not universal. For example, with regard to switchgear, low voltage often means less than 1000 V. Bhulekh Software Download. ) Article 725 is not just about low voltage, nor is it the only article concerned with low voltage circuits. A number of articles cover low voltage circuits and equipment. Article 720 covers circuits and equipment that operate at less than 50 V. Section 720-1, Exception lists other articles that contain provisions for low-voltage circuits and equipment.

Articles 411, 551, 650, 669, 690, 725, and 760 are mentioned. These articles cover low voltage lighting, recreational vehicles, pipe organs, electroplating, solar photovoltaic systems, remote control and signaling, and fire alarm systems, respectively. Other applications of what may be low voltage equipment and circuits are covered by articles 504, 640, 727, 770, 780, 800, 810, and 820. These articles cover intrinsically safe systems, sound recording, instrumentation tray cable, optical fiber cables, closed-loop power distribution, communications, radio and television, and community antenna TV and radio. Of the many articles listed above, a few articles other than Article 725 may apply to instrumentation and control circuits. In particular, Article 504 covering intrinsically safe circuits, Article 727 covering instrumentation tray cable, Article 770 covering fiber-optic cables, and Article 800 covering communications, often apply to some parts of instrumentation installations. So what is Article 725 really about?

The title of Article 725 is 'Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits.' Section 725-1 says Article 725 covers such circuits where they 'are not an integral part of a device or appliance.'

Certainly the description 'remote-control, signaling, and power-limited' covers most instrumentation and control circuits. However, some such systems, such as those using optical-fiber cable, are not Class 1, Class 2, or Class 3 circuits.

An important distinction to be made about circuits covered by Article 725 is given in the Fine Print Note to Section 725-1. Remote control, signaling, and power-limited circuits are quite different from power and lighting circuits. Gadwin Print Screen Crack Prank. Because of the limited loads and limited power sources involved, Article 725 offers modifications of the general rules of Chapters 1 through 4. As noted in Section 90-3, Chapter 7 provides rules for Special Conditions which modify the usual rules. Article 725 allows for special wiring methods,different wire sizes and insulations, and distinct rules about such things as overcurrent protection and derating factors. In turn, Article 725 also restricts the intermixing of remote control, signaling, and power limited circuits with power and lighting circuits.