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Page 185

| Figure 10-7 Pole-mounted air-break switch in open position. |

| exciting) currents from transformers connected to the circuit, or they may represent charging currents from capacitors connected to the circuit. If these currents are large, oil switches may be advisable. |

| As with disconnects, air-break switches may be operated as single-pole units or gang operated in multipole units actuated from a single device (Fig. 10-7). They may be operated by insulated switch sticks or by manual or motor-operated mechanisms. |

| Arcing horns are metal rods attached to the clip or stationary end of a switch but bent at an angle from the path of the blade. As the blade of the switch is opened, the arcing horns remain in contact until after the main contacts have separated. As the switch blade continues to open, an arc is permitted to form between a part of the blade not designed to make contact with the stationary clip and the arcing horn. As the spread between these horns and the blade becomes larger, the arc continues to lengthen until it is finally extinguished through inability to span the gap. Any pitting or burning that may occur takes place on the horns and parts of the switch blade where it is not critical. Although the blade of most air-break switches operates in a vertical plane (though they may be mounted horizontally or vertically), the blade of others operates in a horizontal plane. The advantages claimed for the latter are that they require fewer insulators and have less trouble operating under conditions of freezing rain, snow, and ice, the reason being that stationary contacts, because of their position, are partially protected from the elements. |

| Auxiliary Interrupter Devices.. |

| To permit air-break switches to interrupt larger currents, several devices can be added to them to reduce the effects and duration of the arcs formed. |

| One simple device replaces the rigid arcing horns with a whip attached to the blade. As the switch opens, the whip remains in contact until the blade is part way open. The whip is then released, and its rapid swing extinguishes the arc very rapidly (Fig. 10-8). |

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