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Page 353

| Figure 17-21 Single-phase, reactive volt-ampere-hour meter. |

| Maximeters |

| Ammeters that register the maximum current flowing in a circuit are also available. In these maximeters, a floating indicator is pushed forward by the ammeter needle. When the reading recedes, the floating indicator stays where it was pushed. After it has served its purpose, the floating indicator is returned to its starting position, ready for the next occasion when a maximum reading is desired. Similar meters are designed to read maximum values of voltage, but they are less frequently used than the ammeter type. |

| Clamp-On Meters |

| The clamp-on meter consists essentially of a current transformer with a split core and a rectifier type of instrument connected to the secondary (Fig. 17-24). The rectifier converts the ac to dc so that the measuring instrument is the single moving-coil type that is not only more rugged but has an accuracy equal to or better than that of other types. The primary of the current transformer is the conductor through which the current to be measured flows. The split core permits the instrument to be hooked on the conductor without disconnecting it. |

| This instrument is usually constructed so that voltages may also be measured. Either a switch on the meter or another separate set of terminals is provided to read voltages. Care must be taken that the leads are connected properly to the terminals across which the voltage is to be measured. |

| The instrument provides for a series of current and voltage ratings. Both current and voltage circuits may be energized at the same time, the pointer being deflected by the service indicated on a selector switch. Extreme care must be exercised when using this instrument on high-voltage circuits. So-called hot-line equipment, such as hot sticks and rubber gloves, should be used. When current or voltage values are unknown, the highest value on the range selectors should be used initially. In general, the use of this instrument should be limited to currents not exceding 1000 amperes on services operating |

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