NEC-2017 Section 312.8(B) refers to the wiring space of enclosures for switches and overcurrent devices without specifically mentioning panelboards. However, the most common enclosure is power distribution equipment such as an enclosed panelboard, switchboard or enclosed switch.
NEC 312.8(B)(1) defines two options for using power monitoring equipment in enclosures for switches and overcurrent devices. The first option requires that specific power monitoring equipment be identified on the Certified (Listed) panelboard or power distribution equipment as a field installable accessory. In this instance, a panelboard or power distribution equipment manufacturer designates specific equipment as an accessory using markings inside the respective enclosure. Typically, this information appears on the label identifying the types of Certified (Listed) circuit breakers evaluated for use in a panelboard. That label often includes torque markings and accessory grounding buss kits that also may be field installed. Because the specific equipment is identified on the label inside the Certified (Listed) panelboard or equipment, it means that a device is covered as a field installable accessory by a panelboard or equipment Certification (Listing).
A second option addressed in Section 312.8(B)(1) is a Certified (Listed) kit evaluated for field installation in a specific panelboard or switch enclosure. This is considered a retrofit application. In this situation, a field installed kit is Certified (Listed) for use only in specific panelboards or other power distribution equipment identified in the installation instructions. Only then can the combination of power monitoring equipment and switches and overcurrent devices be considered as compliant with UL’s Certification (Listing) requirements and the NEC and operate as intended.
Another aspect of a Code-compliant installation is sufficient room inside an enclosure to accommodate installation of power monitoring equipment. NEC 312.8(B)(2) requires that the total area of all conductors, splices, taps and equipment at any cross section of the wiring space not exceed 75 percent of the cross-sectional area of that space.
Power monitoring equipment that may be used in accordance with NEC 312.8(B) is Certified (Listed) under the UL product category for Energy-monitoring Current Transformers (XOBA). These current transformers may be used with remotely mounted devices Certified (Listed) under Energy Usage Monitoring Systems (FTRZ).
The energy-monitoring current transformer product category covers open-type current transformers intended for field installation within distribution and control equipment such as panelboards, switchboards, industrial control equipment and energy-monitoring/management equipment to measure current on a branch circuit. These transformers are intended to be installed in accordance with ANSI/NFPA 70, National Electrical Code (NEC), and are investigated for compliance with UL 2808, Outline of Investigation for Energy Monitoring Current Transformers.
The current transformers can then be connected to Certified (Listed) externally mounted energy usage monitoring systems intended to meter utility and nonutility electric power. The primary function of these devices is to monitor power consumption on a building main supply or separate branch circuits. These devices may communicate with other devices via power line carrier, satellite/radio frequency, telephone, cable or other means. The basic Standards used to investigate products in the category are UL 916, the Standard for Safety of Energy Management Equipment, or UL 61010-1, Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use – Part 1: General Requirements, and UL 61010-2-030, Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use – Part 2-030: Particular Requirements for Testing and Measuring Circuits.
As power monitoring equipment and other technologies for use in power distribution equipment evolve, UL will continue to work with industry to expand retrofit certifications. Our focus will be on addressing safety issues related to compatibility and installation to enable customers to deliver a code-compliant installation.
The UL guide information and Certifications (Listings) for Energy-monitoring Current Transformers (XOBA) and Energy Usage Monitoring Systems (FTRZ) can be viewed on UL Product Spec at www.ul.com/productspec. Enter XOBA or FTRZ at the category code search.