10/02/2026
●●● Classification of switches :
● Air-break switch :
• an air switch that is designed to open a circuit under load.
• Used outdoor for circuits of medium capacity such as lines supplying an industrial load from main transmission line or feeder.
• arcing horns are provided to quench the arc that may occurs during the opening of the switch.
• Arcing horns are pieces of metals between which arc is formed during the opening operation and as the switch opens, these horns are spread farther and farther apart.
● Isolator or disconnecting switch :
• It is designed to open a circuit under no load.
• Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while current is flowing in the line.
• Used on both sides of circuit breakers in order that repairs and replacement of circuit breakers can be made without any danger.
• It should not be opened until the circuit breaker in the same circuit has been opened and should always be closed before the circuit breaker is closed.
● Oil switches :
• the contacts of such switches are opened under oil, usually transformer oil to cool and quench the arc that tends to form when the circuit is opened.
• used for circuits of high voltage and large current carrying capacities.