. Journal of electricity. which energizes the tripcoil of the circuit breaker, which must be of the shunttrip type, thus opening the main circuit. When usedin conjunction with an under-voltage release circuitbreaker, the relay is equipped with circuit openingcontacts. In this case the action of the relay is simplyreversed, the auxiliary circuit being opened in eventof a phase reversal and thereby tripping the main cir-cuit breaker. This device will also operate in case ofphase failure due to a blown fuse, broken wire or simi-lar cause. Another type of relay which is described by themanufacture
. Journal of electricity. which energizes the tripcoil of the circuit breaker, which must be of the shunttrip type, thus opening the main circuit. When usedin conjunction with an under-voltage release circuitbreaker, the relay is equipped with circuit openingcontacts. In this case the action of the relay is simplyreversed, the auxiliary circuit being opened in eventof a phase reversal and thereby tripping the main cir-cuit breaker. This device will also operate in case ofphase failure due to a blown fuse, broken wire or simi-lar cause. Another type of relay which is described by themanufacturer as a phase failure and phase reversalprotective device is shown in Fig. 2. In constructionit is much similar to a miniature polyphase squirrelcage motor, but is arranged to be mounted with theshaft in a vertical position. Like the other type of re-lay already described, this device is equipped withcontacts which are connected in series with the auxil-iary tripping or operating circuit of the main circuit CIRCUITBREAKER. U 2 0R3PHA5E - 3 WIRE Pig. 3.—Circuit closing relay with shunt trip breaker interrupting device. Circuit opening contacts arestandard, but circuit closing contacts can also be sup-plied when required. This device is generally used inconjunction with a magnet switch or contactor whichautomatically opens and closes as the contacts in thedevice open or close the control circuit of the manufacturer of this device states that it isdesigned to perform the following functions: (a) If the supply voltage falls below 70 per centof normal, the relay opens the control circuit of themotor controller, and keeps it open until the line volt-age returns to at least 85 per cent of normal. (b) In case of phase failure, caused by the open-ing of one of the supply lines at any point, the relayopens the control circuit, if the motor is under appre-ciable load, and keeps it open until the fault is cor-rected. If the load on the motor is very light, so thatno harm would
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