Installing Smart Switches

Many new concepts in lighting control ARE being used by designers and electricians, while other new designs are still relatively unknown. New switches have been developed that can provide control of individual luminaires or lighting circuits while interfacing with microprocessors that will provide both timing, dimming and mood setting of luminaires in multiple locations. Knowing how to install these sophisticated control circuits in accordance with the National Electrical Code is crucial for both proper operation and the safety of the installation.

Old dimming switches were switches that operated as rheostats and used adjustable resistors to drop the voltage to the incandescent fixture, thus dimming the lights. These old dimmers were either single pole or three-way switches and required physical adjustment of the switch to cause the dimming action. The rheostat dimmer switches were often very bulky and operated at high temperatures, requiring heat sinks to be designed into the dimmer switch housing. The heat sinks for the switches were designed as cooling fins and located on either side of the dimmer. When installing the switch, these heat sinks could be snapped off if more than one dimmer switch was to be installed at a box. Each part of the fin that was removed would decrease the total wattage rating of the switch. The old technology dimmer was not interactive with any other dimmer and only controlled the lights connected to that dimmer.

New and innovative designs for dimming modules, dimming panels and interconnected dimmer switches now permit dimming entire banks of switches in a set pattern or a random pattern, at the discretion of the user, to provide specialty control of luminaires (lighting fixtures). Most new dimmer switches are solid-state devices that are not as bulky as the old rheostat dimmers, operate cooler (but still may have heat sinks designed into the switch), and can be interlinked electronically to provide “smart switching.”

Special individual single pole, three-way, and four-way switches can now be connected to a solid state microprocessor-controlled dimmer bank. The microprocessor can be used with the factory default setting for strictly the “on” and “off” switch function for the circuit. The user or operator of the system also can reprogram the default setting of the microprocessor by changing the software setting to provide dimmer functions as well. The lighting fixtures can then be dimmed or brightened by pressing and releasing the switches. Pressing the switch and holding it down will either increase or decrease the lighting level to highest or lowest level, depending upon the load level curve at which the circuit was operating at the point of activation of the switch.

The system can also be programmed to control a number of circuits from various switch locations. Some manufacturers have used a low-voltage Class 2 control circuit to connect the various switches to the microprocessor. Since the Class 2 circuit connects directly to the switch and the switch is also connected to a 120V circuit, mixing the Class 2 circuit in the same enclosure with the power circuit is normally a violation of the NEC.

However, Section 725.55(D)(1) provides permission to have Class 2 and Class 3 circuit conductors in the same compartments, enclosures, device boxes, outlet boxes or similar fittings with electric light and power circuit conductors where the light or power circuit conductors are routed to maintain a minimum of a 1/4-inch separation from the Class 2 and 3 circuit conductors. Maintaining this 1/4-inch separation in a switch (device) box is extremely difficult, if not impossible.

Section 725.55(D)(2) does provide an alternative that is more feasible. Where the power or lighting circuit entering the device box or the microprocessor enclosure operates at 150V or less to ground and the Class 2 or 3 circuits are installed using Type CL-3, CL-3R, CL-3P, or permitted substitute cables, the power or lighting conductors can occupy the same device box or enclosure without maintaining the 1/4-inch separation. The Class 3 cable jacket must be intact from the connection at the switch to the point where this cable exits the box or enclosure or the 1/4-inch separation must be maintained where the jacket has been stripped. Some manufacturers have RJ-45 male plugs on the Class 3 cable and a matching female jack (connection point) on the switch. This permits the cable jacket to be maintained throughout the installation, thus permitting the lighting and power circuit conductors to mix freely with the Class 3 cables.

Since the lighting circuit is limited to 150V and the Class 3 jacketed cable has a voltage rating of 300V in accordance with Section 725.71(F), safety is not compromised and wiring is held to a minimum. EC

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at




About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and .

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