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| sizes indicated, they are more efficient than incandescent lights and give off less heat. They operate at starting voltages of 600 volts or higher and have small dry-type, autotransformers incorporated with each unit; the unit may contain one or two such lamps. The transformers are designed for operation at 120, 240, and 480 volts, and are supplied with four-line voltage taps of 5 percent each to permit proper adjustment to various line voltages. |

| Sodium lamps are very similar to the mercury lamps, except that sodium is used in place of mercury, and the light given off is yellowish instead of green. |

| Halogen lamps gasify other elements that give off a softer yellow light, are more efficient and are quicker to reach full brilliance than the mercury and sodium vapor lamps. Operating temperatures are very high. |

| For lamps requiring ballasts or transformers, line voltages higher than maximum limit of the range will shorten the life of the lamp and transformer; below the limit will cause uncertain starting, shorter lamp life, and reduce illumination. |

| Motor Starting |

| Practically all ac motors, except those of fractional horsepower, are started at reduced voltage to reduce their starting current. For the usual motor of several horsepower, an autotransformer is used together with switches or breakers to accomplish this purpose. Figure 6-13 shows two methods of connecting these in the motor circuit. Note that the transformer is usually connected to the neutral terminal so as to hold down the voltage that its insulation must withstand. |

| The autotransformers used are under-sized for economy. Since the starting period is usually short, and the rating of the transformer limited by the permissible temperature rise, the amount of current they are designed to handle will be larger than that for continuous operation. Should the starting duty recur at more frequent of very close intervals, it has to be taken into |

| Figure 6-13 Motor-starting arrangement using auto-transformers. (A) One-step connection. (B) Two-step connection. |

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