Figure 20 is a drawing showing the centrifugal short-circuiting device. The mechanism consists of a stationary plate, a movable plate, a commutator, a short circuiting disc, three fly-weights, separator balls, and a retaining spring. The whole mechanism is mounted on the shaft and rotates with it. When the motor is at rest, the retaining spring forces the commutator short-circuiting disc away from the commutator. The force is transmitted from the spring through steel balls to the fly-weights, and they are forced in towards the shaft, as shown in the upper drawing of this figure. In (A) of the same figure is shown a sectional view of the mechanism under this condition. There is a space of about three thirty seconds of an inch between the commutator and the commutator short-circuiting disc.

When the centrifugal switch is in this position the motor will start as a repulsion motor. As the motor gains speed, the fly-weights are forced away from the shaft. The force is transmitted through the separator balls, which force the movable plate and the commutator short-circuiting disc toward the end of the commutator. When the motor speed is nearly up to normal, the short-circuiting disc makes contact with the end of the commutator, short-circuiting all of the commutator segments, and the motor then runs as a single-phase induction motor. The position of the parts of the centrifugal switch mechanism under the running condition is shown in the lower left-hand drawing of Figure 20. Drawing (B) of this figure shows a cross-sectional view illustrating the action of the fly-weight and the separator balls under the running condition.

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