Subsection 725.52(A), Exception No. 2 (NEC 2002), permits installation of Class 2 and Class 3 system conductors in the same conduit with power conductors. The conductors will be inherently coupled, both inductively and capacitively; notwithstanding coupling-independent conductor insulation levels and arbitrary circuit reclassification. Power-conductor faults, transients and other disturbances will be manifested as control circuit coupled voltages — voltages that will exceed Class 2 and Class 3 equipment ratings. Do you think this could compromise life safety and property?
First, there are some fine points in the referenced section that must be made. Section 725.52(A) does not permit Class 2 and Class 3 conductors to be in the same conduit with power conductors. It allows Class 2 and Class 3 circuits to be reclassified and installed as Class 1 circuits. The Fine-Print Note then points out that these are now Class 1 circuits, which means they must use Class 1 wiring methods and must comply with Class 1 rules. The basic rule of 725.52(A) just permits the use of Class 1 wiring methods, in which case the circuits remain Class 2 or Class 3 and the separation requirements for Class 2 and Class 3 circuits found in 725.55 remain in force. The exception permits reclassification. Once the circuits are reclassified, the permission to mix Class 1 circuits with power circuits in a raceway (conduit) is found in 725.26(B)(1) and this permission requires that the Class 1 and power circuits be functionally associated, in other words, the power and control conductors are both for the same equipment.
The effect of the new rule in 2002 is to permit something that was generally not clearly or specifically permitted in the past, but was occasionally required by Section 725.8 for safety control equipment. Since we were required to reclassify and use Class 1 methods for certain safety controls, where reliability was especially important, we should be permitted to use similar methods for less critical applications. Reclassification has also long been permitted for Fire Alarm Circuits under 760.52(A), Exception No. 3. The new rule in 725 permits the use of the Class 1 methods with the circuits remaining Class 2 or 3, or it permits the reclassification of the Class 2 or 3 circuits as Class 1, which is essentially the same treatment given to PLFA Fire Alarm Circuits.
Your concerns about the equipment ratings of Class 2 and Class 3 equipment are valid concerns. Code making Panel 16 has turned down proposals for reclassification or use of ordinary wiring methods in the past and cited similar concerns to those you pose. In many cases, Class 2 equipment will have to be modified or different equipment would have to be used if the circuits are reclassified as Class 1. For example, many Class 2 transformers are designed to be installed with the output terminals exposed, boxes are not required to enclose splices in Class 2 conductors and many types of Class 2 devices have exposed terminals. When these circuits are reclassified as Class 1, all the splices and terminations will have to be enclosed, because, as you point out, if the circuits separations are not maintained, we cannot be assured that the power levels will remain at the less hazardous Class 2 levels. Similarly, a Class 2 control device, such as a thermostat or a gas valve, may have exposed energized parts or terminals that are no longer safe when connected to Class 1 circuits, and equipment that was not required to be grounded when the circuits were Class 2 will be required to be grounded as Class 1. Since the same may be said for other connected equipment, reclassification of circuits may require some additional work on the part of the designer to be sure that all the equipment is compatible with the possible higher energy levels and can actually be installed as required for Class 1 circuits.
The substantiation for the proposal and the panel statement concentrated on the desired permission to use ordinary (Class 1) wiring methods (wire in conduit, typically) with Class 2 or Class 3 circuits rather than being required to use CL2 or CL3 cables. This presents none of the issues you mentioned, because the circuits remain Class 2 or 3 and the separation requirements continue in effect so the energy levels are not compromised. Nevertheless, the new rule is not unsafe, but it requires careful consideration by the designer or installer if a Class 2 circuit is to be reclassified and installed as Class 1.
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