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Page 101

| Figure 6-12 Sign lighting, two winding, transformer with midpoint of high voltage secondary winding grounded. |

| grounded, connected as shown in Fig. 6-12. This enables twice the length of tube to be served using a voltage measured from ground of only half the required value. For safety reasons, the voltage from these transformers is usually limited to a maximum of 15,000 volts. Where the tubing for the sign may be too long to be adequately supplied at this voltage, it is sectionalized into lengths which may be supplied safely. As an additional safety feature, the transformer may be placed physically on or near the sign near the middle of the total length of tubing to be served, to keep the lengths of cable operating at high voltage as short as possible. The transformers may be oil filled for outdoor use and air cooled enclosed types for indoor use; these latter have their high-voltage terminals usually sealed so that they cannot be readily accessible and may be so arranged that the primary circuit is automatically deenergized when the enclosure is opened. |

| Fluorescent Lighting.. |

| Fluorescent lamps operate somewhat similarly as the gas tubes described above. They are fixed dimensions and the voltage applied is raised from the usual normal 120 volts secondary supply by a ballast which is incorporated in one end of the fixture in which the fluorescent tube is installed (the ballast is essentially a small autotransformer designed for the specific lamp size). Standard ballasts are designed for ranges of 110125 volts, 199216 volts, and 220250 volts. |

| Mercury, Sodium and Halogen Lamps |

| Mercury lamps are high-intensity lights and sizes run from 400 watts to 3000 watts. They operate on the principle of vaporizing a pool of mercury into gas, and the current carrying vapor (ionized gas) gives off a greenish light. For the |

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