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Page 53

| Figure 3-11 Lightning arrester on riser connected to underground transformer. |

| Customer Installations. |

| Transformers for specific customer installations have a wide range: from small bell ringing and sign lighting where the high voltage may be 120 or 240 volts and amounts limited to a few amperes to x-ray equipment where high voltages range into the several thousands and welding and electric furnaces where values of current are measured in thousands of amperes. Their installations are covered in the National Electric Code and in local codes and regulations. In general, however, the safety precautions are similar to those for power installations described above. Where fire hazards are of paramount importance, dry air-cooled transformers are installed for modest requirements, air blast or askarel cooled units for large loads. |

| In all cases. special attention is given to the proper ventilation of these units and the safe grounding of transformers and appliance enclosures and neutrals. |

| Autotransformers.. |

| Autotransformers are often used in place of two-winding transformers. These will be described in Chap. 6. Their installation, however, follows closely the same requirements as two-winding transformers. |

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