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Power circuit breakers for voltage services of 2,300 volts and above use either of two basic principles to complete circuit interruption. The more familiar types, oil breakers or compressed air breakers, complete their operation by maintaining a low resistance arc until the final current zero where interruption is completed. Magnetic air circuit breakers establish a high resistance arc prior to circuit interruptions which modifies the circuit constants before recovery voltage is established. The “Magne-blast” breaker falls in this second class of breakers. The treatment of the arc in this breaker to obtain a high arc resistance is explained in some detail. Also, design practices and operating characteristics of the final magnetic type breaker are reviewed.