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Page 346

| Figure 17-15 Typical watthour meter (Courtesy, Westinghouse Electric Co.) |

| Reactive Volt-Ampere-Hour Meters |

| Meters to measure reactive volt-ampere-hours are essentially ordinary watt-hour meters with reactances added to displace the voltage applied by 90°. A schematic diagram for a basic single-phase reactive volt-ampere-hour meter is shown in Fig. 17-21. Similar principles apply to two-phase and three-phase meters. |

| Demand Meters |

| The maximum demand of an installation may be obtained by adding another dial and set of gears to the watthour meter. There are two hands on this dial, one of which is connected to the actuating mechanism and the other of which just floats, being pushed along by the first hand. The first hand measures the number of revolutions made in a standard period of time, usually 15 minutes (in special instances, a half hour or hour). At the end of this period, another mechanism operates to return the first hand to zero, and the process starts all over. In the meantime, the second hand having been pushed by the |

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