. Electrical news and engineering. instruments consist of any two standard type AW or typeF\\ instruments desired, mounted in an attractive dull-blackmetal case. The type AW instnmients liave round openfaces, three inches diameter, with glass cover and rearmounting studs; the type FVV have five-inch faces. A Protection Against Reversed Phases If a three-phase motor is disconnected from a circuit andthe phases reversed when it is reconnected, it will, naturally,run backward. Such a reversal may occur and has occurredwhen the motor is disconnected for repairs, through an errorin reconnecting lea
. Electrical news and engineering. instruments consist of any two standard type AW or typeF\\ instruments desired, mounted in an attractive dull-blackmetal case. The type AW instnmients liave round openfaces, three inches diameter, with glass cover and rearmounting studs; the type FVV have five-inch faces. A Protection Against Reversed Phases If a three-phase motor is disconnected from a circuit andthe phases reversed when it is reconnected, it will, naturally,run backward. Such a reversal may occur and has occurredwhen the motor is disconnected for repairs, through an errorin reconnecting leads at the power house, or sub-station, orfrom a number of other causes. In many cases the reversalof rotation of a motor, aside from the inconvenience it causes,is not a serious matter as the error can be corrected at the. Illustfation of relay. motor terminals. In other cases, however, serious consequ-ences may result. The reversal of an elevator motor, forinstance, might result in wrecking the machinery and loss oflife. To protect motors against phase reverse where suchprotection is necessary, the Westinghouse Electric & , have developed a reverse-phase relay with very positive THE ELECTRICAL NEWS Oi-tnlier 1, ami doiK-iiilalilc upLratiiig oliaractcristics. 11 a pliast- Is rr-versed, or if a phase fails, nr if thu vultaije drojis In-low 7>per cent of normal, the relay contacts close and trip the cir-cuit-breaker, either through a shunt-trip coil or by short-circuiting an undcrvoltage trij) coil having a series reverseresistor. The relay operates on the induction ])riiperly connected the tortiue holds the contacts open . R2S!Slor-xAA/WV ■^ UndQrKll^<l(;^Trip Coil. To Trip Circuit
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