As part of the development of the low-voltage lighting power-grid system, coverage and acceptance of the new system within the standards community becomes paramount, since this product is new and innovative. New products and their designers often find themselves in uncharted territory, since designers must ensure their products adhere to accepted safety procedures, but new products will often require new standards and altered installation codes. Suspended-ceiling-grid low-voltage lighting systems were developed first, and Underwriters Laboratories Inc. established an outline of investigation. This covers the suspended-ceiling grid low-voltage lighting systems and components intended for permanent installation and use in a suspended-ceiling grid in accordance with Article 411 of the National Electrical Code (NEC).

The low-voltage lighting distribution system is designed to be installed as part of a suspended-ceiling grid that provides mechanical support for the ceiling tiles. In addition, the grid provides electrical connections from the low-voltage power supply to the grid and, thus, to the low-voltage luminaires. The low-voltage lighting system consists of an isolating-type low-voltage power supply operating at 30 volts (V) rms (42.4V peak) or less and not exceeding the Class 2 power limits as outlined and provided in Parts I and III of Article 725. The Class 2 powered luminaires may be recessed into the suspended ceiling, may be surface-mounted on the room side of the ceiling, or may be located below the suspended ceiling but receive their power from the grid. The low-voltage lighting distribution system is intended to be permanently connected in an indoor dry location within a commercial facility.

The outline of investigation has pertinent definitions that apply to the specific application of a low-voltage power grid. Mechanical construction requirements determine the strength of the grid and connectors plus assembly and mounting. There are electrical construction requirements for the grid’s current-carrying capacity, the splices, power-feed connectors and Class 2 power supply transformers.

In addition, 725.136 states Class 2 conductors must be separated from power circuits. The outline of investigation also requires performance tests, such as connector-cycle conditioning and temperature tests and mechanical-assembly load tests to indicate the amount of grid twisting that could occur. System flammability also is an issue for grid rails and connectors installed in air handling spaces or for exposed finished ceiling side, so testing is required to ensure the system’s nonflammability. Finally, there are marking requirements with installation and operating instructions for the overall low-voltage lighting power ceiling grid.

The system’s basic design, while considered new and innovative, can easily fit in the existing text within the NEC. The Class 2 power supply and wiring system is covered by the appropriate requirements in Article 411 for lighting systems operating at 30V or less and associated components. The definition of lighting systems operating at 30V or less is located in Section 411.2 and is defined as a lighting system consisting of an isolating power supply, the low-voltage luminaires and associated equipment identified for low-voltage use.

The outline of investigation and the NEC provide the technical information and background for installation and use of suspended-ceiling-grid low-voltage, lighting systems. There are other, much broader applications for these ceiling-grid low-voltage lighting systems. A glimpse into the future indicates that a low-voltage suspended-ceiling-grid power-distribution system can supply countless other devices in many different aspects of daily living within an office environment.

The low-voltage grid system can be used for various low-voltage power sources to supply in-wall audio/video systems, office furniture, security systems and occupancy sensors. Ceiling-tile-type speakers can be connected with music and other communication signals inserted onto the direct current (DC) supply on the grid and then tapped off to provide for easy surround-sound for audio applications.

With the advent of new solar photovoltaic technology, window panels with solar photocell coatings could provide power to the suspended-ceiling grids. Building management control systems for lighting, heating, cooling and all other aspects of building functions could be controlled using a suspended-ceiling-grid distribution connection to the building’s energy management system. Fire alarm devices could be installed to a permanent source of DC supply with location and connection made just as conveniently and as easily accomplished as the installation of wireless fire alarm devices but with much more reliability than, for example, a wireless battery-powered smoke detector. Some people say the future is here.


ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and mark.c.ode@us.ul.com.