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| Figure 6-9 Current transformer connection. |

| transformers, and can have several items connected to it so long as its burden, rated in amperes, is not exceeded. |

| Because of the high turn ratio usually met with in a current transformer, it is possible to obtain an unsafe high voltage across the secondary terminals of the current transformer. The regulation of these transformers, however, is designed so that the voltage drops very rapidly as soon as the ammeter or other burden is connected to it. For safety reasons, therefore, the terminals of the current transformer should always be short-circuited when instruments are not connected to it; the instruments should first be connected before the short-circuit strap is removed. |

| Both potential and current transformers may be of the dry-type or oil-filled. They may be equipped with solid porcelain or oil-filled high-voltage bushings, through which the high-voltage leads are brought out of their case. Windings are insulated from each other in a similar manner as other transformers. Their construction must also be sufficiently rugged to carry short duration fault currents safely. |

| Street Lighting Transformers.. |

| Street lighting may be served from multiple circuits or from series circuits. In the first, the lamps are connected across the two conductors of the circuit, much as the rungs of a ladder connect to the runners on both sides. This is the type of circuit that commonly exists in houses, offices and factories, supplied from two-winding distribution transformers previously described. In the second or series circuit, the lamps are connected in succession, like beads on a string, so that whatever current passes through one passes through all of them. This type circuit cannot be supplied from the usual distribution transformer, but requires a transformer which will produce a constant current, but with a voltage at the outgoing terminals which will vary in magnitude proportionately to the load, or number of lamps, it is called upon to supply. Such a transformer is known as a constant-current transformer, and is usually designed to supply a current of 6.6 amperes, the values designed to give optimum operation of the lamps. |

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