Shown below is a plant having two manufacturing bays and a storage bay. The service designated is 480Y/277 Volt three-phase, four wire.
We assume that the work in the two manufacturing bays will include general fabrication and assembly work, automatic machining and inspection. Lighting recommendations of the Illuminating Engineering Society (IES) are shown along with the approximate volt-amps per square foot required to provide the light. The foot-candle level required is 100 FC for the two manufacturing bays and 30 FC for the storage bay. Metal halide lighting will be used because it is efficient and the job requires good color rendition. Each manufacturing bay will require 80 kVA of lighting and the storage bay will require 24 kVa. Bays are 100 feet x 200 feet in size. (Refer to Table 22A of TEC for Average Lighting Load.)
Specifying the wiring for the storage area should consider whether this area might possibly be used for manufacturing in the future, say five years. Therefore, for the purpose of this example, we will assume that the area will be used for manufacturing within five years. Therefore, the storage area will be wired for 80 kVa as well.
We will also want to provide 10 kVa at 120/240 Volts, single phase for convenience outlets for small tools in each bay. This load is usually connected at the lighting panels. The total lighting load for the plant will be 240 kVa plus 30 kVa for outlets.
Three lighting feeders will run from the service equipment to lighting panels centrally located in each bay to reduce branch circuit length and voltage drop. Each lighting panel will utilize four-wire, 480Y/277 Volt feeders to supply the 277 Volt ballasts. The branch circuit neutral is required. Each lighting panel will also supply a 10 kVA, 480-120/240 Volt dry-type transformer to provide the 120/240 Volt single-phase supply.
