310-15(b)(2)(a) and the accompanying table apply only if such conductors carry continuous loads in excess of 10% of the ampacity of each control conductor routed through the raceway system. 725-26(b) allows mixing for underground conductors in a manhole if you comply with all of the following conditions: (1) The power-supply or Class 1 circuit conductors are in a metal-enclosed cable or Type UF cable (2) 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 and (3) The conductors are permanently and effectively separated from the power supply conductors and securely fastened to racks, insulators, or other approved supporting means.ĭerating requirementsWhere only Class 1 circuit conductors are in a raceway, you can determine the number of conductors by the provisions outlined in Sec. 725-26(b) clarifies you can mix these circuits when installed in factory- or field-assembled control centers. One example is when the power supply conductors and control circuit conductors are run in the same conduit to control and operate the same piece of equipment, such as a motor controller.Įxception 1 to Sec. The NEC allows Class 1 circuits and power supply circuits to occupy the same cable, enclosure, or raceway in situations where the equipment power system is functionally associated. Class 1 signaling circuits are used in nurses' call systems in hospitals, electric clocks, bank alarm systems, and factory call systems.Ĭlass 1 circuits can occupy the same cable, enclosure, or raceway without regard to whether the individual Class 1 circuits are AC or DC, provided all the Class 1 conductors are insulated for the maximum voltage of any conductor in the cable, enclosure, or raceway. We commonly use Class 1 remote-control circuits in motor controllers (which operate mechanical processes), elevators, conveyors, and in equipment controlled from one or more remote locations. Generally, Class 1 remote-control and signaling circuits must meet most of the same wiring requirements for power and light circuits. A transformer or other type of power supply supplies power to Class 1 circuits. This limiter is an OCPD that restricts the amount of supply current on the circuit in the event of an overload, short circuit, or ground-fault.
Class 1 remote-control and signaling circuits are limited to 600V, but there are limitations on the power output of the source.Ĭlass 1 power-limited circuits have a current limiter on the power source that supplies them. Power-limited Class 1 circuits are limited to 30V and 1000VA. The NEC divides Class 1 circuits into two types: power-limited and remote-control and signaling circuits. These circuits are also classified in accordance with their respective voltage and power limitations.
These circuits are characterized by their usage and electrical power limitation, which differentiates them from light and power circuits. The NEC defines such circuits as that portion of the wiring system between the load side of the overcurrent protection device (OCPD) or the power-limited supply and all connected equipment.
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Note: This article is based on the 1999 NEC.Ĭlass 1, 2, and 3 circuits are classified as remote-control, signaling, and power-limited circuits in the National Electrical Code (NEC). If you’d like to see updated information on this topic, please check out these more recently published articles: Brushing Up on Class 1 Circuit Requirements and Class 2 Circuit Requirements. Thank you for visiting one of our most popular classic articles.
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