At a recent National Electrical Code (NEC) update seminar, 
I was asked about the new requirements to install a grounded (neutral) conductor in a box for switches that control lighting loads. The question identified a need for clarification of the existing NEC requirements, which went like this: “The Code requires me to install a neutral conductor in the boxes for switches controlling lighting loads with some exceptions, but the requirement does not indicate I have to connect the required neutral to a device. Can you explain why the neutral has to be installed and why there is no requirement to use it?”


The question was interesting because it indicates improvements are still necessary to address the real concerns behind the requirements. First, let’s address the requirement and why it was included in the 2011 NEC. Many new electronic devices—such as occupancy sensors, timers and so forth—require a 120-volt (V) circuit to operate the electronic circuit board in the device. This requires a standby current to maintain the ready state and detection capability of the device. Standby current is present at all times, even when the lighting load being controlled is off. This allows “the brain” of the device to stay active to switch the device to the on position.


In most dwelling units and commer-­cial installations, grounded (neutral) conductors are not installed in the switch boxes for devices controlling lighting loads. Therefore, these control devices had to be designed to use the equipment grounding conductor to conduct the standby current. UL 773A permits these occupancy sensors to have a current of up to 0.5 milliamperes (mA) on the equipment grounding conductor. This is a currently acceptable provision in the product standard for these types of devices and has not been revised. These devices have become quite popular, and existing product standards permit them to use the equipment grounding conductor as a current-carrying conductor. This is generally not an issue in residential occupancies, but it can be a significant problem in larger commercial applications where many of these devices are installed on the system. The current on the equipment grounding conductor can be additive in these situations and can exceed the 0.5 mA level.


Escalating energy costs and the increased energy-saving codes adoption promote and, in many cases, legislate that these products are intended to reduce energy consumption. The new rule in the NEC clearly portrays the identification of an unsafe practice by mandating the inclusion of a grounded (neutral) conductor at switch locations other than those described in list items 1 through 7 to 404.2(C). This requirement is not limited to a location, and the challenge is that an occupancy sensor device may be installed initially or as an improvement at any time and at any switch location. The problem appropriately identified in the question is that the NEC does not specify use of a device that includes an insulated neutral for connection other than in the informational note, which is not a requirement. Consequently, the UL standard for these types of devices has not been revised to support and coordinate with this change in the NEC. These electronic devices continue to be manufactured and listed as before; however, some manufacturers produce them with an insulated neutral, and some manufacturers produce both types.


There are two problems here. First, the Code has to specify the type of electronic switch that includes a means for an insulated neutral conductor connection. Second, the product standard ultimately should be revised to not permit production of the types of devices that use the equipment grounding conductor of the branch circuit for completing the 120V circuit that supplies the electronic circuit (brains) of the device.


The intent of this Code rule is to require an insulated neutral to be installed at switch locations and that it be used to connect a suitable, listed electronic device either at the time of the initial installation or when installed at a later date. The neutral requirement is included in the NEC as a means to address new installations. Still missing in the Code is a requirement for electronic switches to include a neutral for the standby current for new installations and an exception that permits older style electronic switches for existing installations where no neutral exists.


In summary, this question raises an important point about changes in the installation Code and product standards: there is more work to be done in the NEC and apparently in the product standard as well. The two have to align and correlate without conflict, and they must clearly indicate what must be accomplished from a performance perspective so that the prescriptive requirements in the NEC are both effective and clearly understood.