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Power Line Carrier (PLC) lighting control allows automatic dimming and on/off control of software defined groups of fluorescent lamps without requiring signal wiring.

The block connection diagram for wye connected branch lighting circuits is shown below. Typically three branch lighting circuits of different phases share a common neutral and a common backbone conduit.

The area to be lit is divided into illumination zones. In each zone an occupancy sensor integrated with an illumination sensor forms a ceiling mounted Sensor Unit (S). Remote occupancy sensor heads may be connected to a Sensor Unit to extend its area of coverage.

When a zone is occupied, as determined by an occupancy sensor in the zone, the operating level of the Ballasts (B) in the zone is automatically controlled by the illumination sensor in the zone. When a zone is unoccupied the illumination level in the zone is set to a programmed minimum or the Ballasts are turned off.

Typically one illumination zone is one office, one meeting room, etc. Illumination zones are chosen such that it is reasonable to control the output of all the lamps in a zone from one ceiling mounted illumination sensor located in the zone.

The Sensor Units (S) are connected to the branch lighting circuits and communicate with the Ballasts (B) using Power Line Carrier signalling.

Wall mounted Control Units (C) communicate with Ballasts (B) and Sensor Units (S) using bi-directional power line carrier signalling. Field programming of the equipment is done by connecting a PC to a Control Unit (C). Control Units may also be used for manual on/off control, manual occupied/unoccupied control and manual adjustment of light level as may be required for use of computers, projectors, etc. Control Units are also used for passing data from one branch lighting circuit to another via an LCS-4 panel.

Each Ballast (B) contains dimming circuitry and a PLC data transceiver. The Ballasts have factory programmed individual codes and field programmed zone codes.

Circuit Filters are installed between the lighting circuit breakers and the branch lighting circuits. The function of the Circuit Filters is to prevent external electrical interference to the desired PLC signals on the branch lighting circuits and to prevent the desired PLC signals on the branch lighting circuits from interfering with external equipment. The Circuit Filters are engineered to produce a very low voltage drop at 60 Hz, to provide power factor correction at 60 Hz and to present a relatively high impedance to the branch lighting circuits at PLC frequencies.

There are three types of Circuit Filters: Standard, Premium and Super Premium. There are application rules for determining the Circuit Filter type that is appropriate for each situation.

Many commercial buildings utilize wye connected lighting circuits in which three branch lighting circuits of different phases share a common neutral and a common backbone conduit. In these circumstances one three phase Circuit Filter can be used to replace three single phase Circuit Filters, thus minimizing the number and cost of the filter components.

The block diagram shows an LCS-4 panel in dotted lines. This panel is a planned future development to permit data exchange between different branch lighting circuits and to permit interface between the PLC Lighting Control System and a central energy management system. The LCS-4 panel will also provide time/day/date control of common area lighting and will permit recording of energy usage. In the absence of the LCS-4 panel, Sensor Units, Control Units and Ballasts can only communicate with one another if they are connected to the same branch lighting circuit.

In order to prevent radiated PLC signals interfering with external equipment and to prevent radiated interference to the PLC signals from external equipment the entire lighting circuit should be encased in a continuous grounded metal shield and there should be no ground faults on the load side of the Circuit Filters. This shielding requirement is normally met by the use of 3/4 inch diameter Electrical Metalic Tubing (EMT) for the backbone lighting circuit conduit and 3/8 inch diameter metal flex or armoured cable for the drops to the Ballasts, Sensor Units and Control Units. The backbone conductors are recommended to be #12 AWG copper with 600V T90 PVC insulation and the drop conductors are recommended to be #14 AWG copper with 600V T90 PVC insulation. Ground wires within the metal flex are used to ensure ground continuity.

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This web page last updated September 20, 2005

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