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Page 357

| Figure 17-23 (cont.) Typical recording meters: (C) graphic demand meter. |

| regardless of the primary rating. At lower ratings, the primary of the CT is connected directly in series with the conductor. At higher ratings, the line itself is used as a single-turn primary and the CT may have its secondary coil shaped as a doughnut through which the conductor passes. |

| Since a current transformer has a small number of primary turns (as low as one) and many secondary turns, the result is to step down the current and step up the voltage. Normally, a high voltage is short-circuited through the low impedance of the instruments and does not build up. If the instruments are disconnected and the secondary of the CT left open, high voltages will occur. The secondary of a CT, therefore, should never be opened while the circuit is energized. |

| Shunts are usually confined to dc circuits but may be used on ac circuits. CTs are used only with ac circuits. One-to-one ratio CTs are sometimes used if |

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