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Page 367

| Make sure that the secondary circuit of a current transformer is never opened while current is flowing in the primary winding; otherwise, dangerously high voltage will result. The secondary winding should be short-circuited when instruments are being changed or when they are not in use. Disconnect the secondary winding from the line before making primary connections. |

| If a clamp-on ammeter is used, make sure that the split transformer core is completely closed or joined together. |

| To overcome slight stickiness, an instrument may be tapped lightly. If movement of a pointer is erratic and tapping moves it appreciably, the instrument bearings or pivots may need attention. If necessary, they should be repaired by a competent facility or returned to the manufacturer. |

| Do not use instruments in strong magnetic or electrostatic fields (such as near cables, buses, unshielded capacitors) unless they are designed for such treatment. |

| Try to take the instrument reading between the one-half and the three-quarters scale value. |

| Read directly at right angles to the instrument so that the needle and its image in the mirror (if one is provided) coincide. |

| Use a damp cloth to clean the glass of an instrument. A dry cloth may induce a static charge and affect the instrument reading. Breathing on the glass may discharge the static charge. |

| Do not slam instrument covers. Make sure that binding post nuts are tight, even when an instrument is not in use. |

| If an instrument is overloaded or dropped or its accuracy is in doubt, check it against another at several points on the scale before using it again. |

| Slide, do not drop, an instrument into its carrying case. |

| Store instruments in a place free from dust, corrosive fumes or other polluted atmosphere, and excessive humidity. |

| Arrange instruments and leads to avoid knocking the former from a table or tripping over the leads. In measuring high voltages, make sure that no one will accidentally come in contact with any energized parts. |

| Do not carry more than one instrument in one hand. If means are provided for locking the moving element, it should be locked before the instrument is transported. |

| Review.. |

| 1. By measuring the values of electrical quantities involved, operators can determine whether circuits and equipment are operating safely and efficiently. Comparing these values with predetermined design specifications and with previously experienced values, troublesome conditions may be detected before they occur. |

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