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Page 284

| plunger. All loose connections and mounting screws, bolts, and nuts should be tightened. The armature or plunger mechanism should move freely without binding or dragging. If alignment cannot be made, the coil or armature or plunger should be replaced. |

| Some relays are replaced in the field and brought to the shop or laboratory for maintenance. When a relay is removed for any reason, extreme care should be taken in tagging and identifying both its terminals and the associated connecting leads. When the relay is reinstalled, corresponding leads and terminals should be carefully reconnected. |

| Relay testing. Relays must be checked periodically, and usually in conjunction with other maintenance, for proper current and time settingsusually by connecting them in series with a test kit that permits current flow to be adjusted to proper values and times the closing of contacts with a stop watch or timer (Fig. 14-17). |

| Instrument Transformers |

| Instrument transformers are used to reduce voltage and current to values that can be handled safely in relay, control, and metering systems. This reduction by a predetermined proportion permits power circuits to be essentially reproduced in miniature scale models. The loads that they are permitted to carry while still maintaining their desired accuracy are referred to as their burden, rated in amperes. |

| Both potential and current transformers must be insulated to withstand the voltage of the power lines to which they are connected and must be rugged enough to carry short-duration fault currents. |

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