Those of us who use the National Electrical Code (NEC) on a regular basis and are familiar with the words as well as the intent of the text can often overlook the most obvious interpretations by the rest of the electrical industry.


I was recently approached by a very knowledgeable NEC person who had a question about 725.130(A) covering wiring methods and materials for the load side of Class 2 and Class 3 power sources. His question involved the actual text as it applies to using Class 1 wiring methods and materials on the load side of Class 2 and Class 3 power sources and the exception permitting the Class 2 or Class 3 power sources to be reclassified and installed as Class 1 circuits. I answered his question by stating the text in 725.130(A), Exception No. 2 permits this reclassification.


He countered by saying that, while he agreed with me about the intent, he had issues with the wording. Since this exception was inserted into the 2002 NEC when I started on Code-Making Panel 3 as an alternate member, I told him I would research this issue and respond with both the history of this exception and an evaluation of the text permitting this reclassification.


There is a long history of Class 2 or Class 3 circuits being installed in dwellings, commercial and industrial facilities with this application dating back into the early days of the NEC when batteries were often used for low-voltage signaling, control and power-limited applications. Use of batteries as the sole source of low-voltage circuits is certainly a thing of the past.


The definition of a Class 2 circuit is located in 725.2 as follows: “The portion of the wiring system between the load side of a Class 2 power source and the connected equipment. Due to its power limitations, a Class 2 circuit considers safety from a fire initiation standpoint and provides acceptable protection from electric shock.” In other words, for most dry locations, the Class 2 circuit with 150-volt-rated insulation does not have fire or shock potential.


Class 3 circuits are defined as “the portion of the wiring system between the load side of a Class 3 power source and the connected equipment. Due to its power limitations, a Class 3 circuit considers safety from a fire initiation standpoint. Since higher levels of voltage and current than for Class 2 are permitted, additional safeguards are specified to provide protection from an electric shock hazard that could be encountered.”


In both Class 2 and Class 3 applications, conductor insulation by itself is not considered to be an acceptable separation from any power circuits. A Class 1 circuit can be either power-limited by a maximum 1,000 volt-amperes power source with up to 30 volts (V) and 33.3 amperes in the circuit, or unlimited current and a maximum of 600V for the circuit. While Class 3 is a shock hazard but not a fire hazard, Class 1 circuits are both shock and fire hazards.


The text and exception in question, 725.130(A) and Exception No. 2, were inserted into the 2002 NEC so designers, installers and users can reclassify Class 2 and Class 3 circuits and use them as Class 1 circuits. An example of this is where a single raceway with power conductors penetrates a concrete roof to supply air conditioning units, and a thermostat control circuit must accompany the power conductors.


The text in Exception No. 2 states that “Class 2 and Class 3 circuits shall be permitted to be reclassified and installed as Class 1 circuits if the Class 2 and Class 3 markings required in 725.124 are eliminated and the entire circuit is installed using the wiring methods and materials in accordance with Part II, Class 1 circuits.”


Section 725.124 requires the electrical equipment to be “durably marked where plainly visible to indicate each circuit that is a Class 2 or Class 3 circuit.” So, any Class 2 or Class 3 markings are to be removed. The exception also states that the entire circuit must have Class 1 wiring methods and materials. An informational note states that “Class 2 and Class 3 circuits reclassified and installed as Class 1 circuits are no longer Class 2 or Class 3 circuits, regardless of the continued connection to a Class 2 or Class 3 power source.” The Class 2 or Class 3 power source must have these markings removed.


The real issue about all of this is the base text in 725.130(A) that sends the user back to “the installation shall be in accordance with 725.46.” The text in 725.130(A) should refer back to 725.46 through 725.51 to provide Class 1 circuit conductors and wiring methods.