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Page 186

| Figure 10-8 Air-break switch with whip arcing horn. |

| Other devices employ interruption chambers or arc tubes and vacuum modules (Fig. 10-9). After the main contact is open, the arc is extinguished (1) within the interruption chamber or arc tube or (2) within the vacuum module, both of which are mounted on the end of the switch blade. The theory behind the former of these devices is similar to that behind the explosion chamber in a circuit breaker. The action of the latter device is similar to the action of the vacuum module in a circuit breaker. In both these types of units, the arc is contained and extinguished within the interrupting device at the time of circuit interruption. Supposedly, these units are faster, more positive, have reduced fire hazard, and are less affected by weather. |

| Contacts |

| Contacts for air switches fall generally into two types, one based on line contact and the other on area contact. |

| Line contact (Fig. 10-10) is usually achieved by the switch blade's being rotated within the stationary contacts and essentially resting under pressure at right angles to the inner side of the clips. The wiping action as the blade turns not only cleans the contacts but clears them of ice formations. The line contacts established are further enhanced by silvering the contact areas of |

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