Figure 6-22. - Photoelectric cell control circuit.
that the street circuit can carry is 240 volts times 6.6 amperes or 1.584 kilowatts.
Figure 6-21 shows the maximum number of series lamps in the various sizes that may be used for full-load rating on a regulator. The average number of watts of energy consumption for each size lamp may be computed since the regulator ratings are based on their output. In this manner, the load of a circuit consisting of different size lamps may be computed.
Example: What size regulator would be required to supply the following lamps?
25 - 1,000-lumen, 6.6-ampere, straight-series lamps
50 - 2,500-lumen, 6.6-ampere, straight-series lamps
10 - 6,000-lumen, 20-ampere lamps with isolating transformer
Solution: Figure 6-21 shows that the average energy consumption of a 1,000-lumen, 6.6-ampere, straight-series lamp with film cutout is 69 watts per lamp. In a similar manner, the average energy consumption of a 2,500-lumen lamp is 167 watts, and a 6,000-lumen, 20-ampere lamp with isolating
Figure 6-23. - Cadmium-sulfide cell control circuit,
transformer is 405 watts. Totaling the combined load shows the following:
25 x 69 = 1,725 watts
50 x 167 = 8,350 watts
10 x 405 = 4,050 watts
14,125 watts or 14.1 kilowatts
Therefore, a 15-kilowatt regulator would be required.
The table makes allowances for line losses in the average series street circuits.
Several methods are used to control the operation of area lighting systems. For recreational lighting, only a manual switch is required. On the other hand, streetlights and security lights have more sophisticated controls.
Lights normally are on during the hours of darkness or when unusual weather conditions indicate the need for artificial light. Although lights could be activated by assigning an individual to operate the controls manually, they are usually turned on and off by a combination of controls.
Most control circuits that you will encounter in the field use one of the following devices to control the lighting system: photoelectric cell (fig. 6-22), cadmium-sulfide cell (fig. 6-23), time clock, pilot wire relay (fig. 6-24), or cascading relays (fig. 6-25).Continue Reading