The worst effects of a Russian high altitude test occurred on 22 October 1962 (during the Cuban missile crisis), in Operation K when a 300 kiloton missile-warhead detonated west of Dzhezkazgan (also called Zhezqazghan) at an altitude of 290 km (180 mi). The Soviet scientists instrumented a 570-kilometer (350 mi) section of telephone line in the area affected by the detonation in order to measure electromagnetic pulse effects.[2]
The EMP fused all of the 570-kilometer monitored overhead telephone line with measured currents of 1500 to 3400 amperes during the 22 October 1962 test.[3] The monitored telephone line was divided into sub-lines of 40 to 80 kilometers (about 25 to 50 miles) in length, separated by repeaters. Each sub-line was protected by fuses and by gas-filled overvoltage protectors. The EMP from the 22 October (K-3) nuclear test caused all of the fuses to blow and all of the overvoltage protectors to fire in all of the sub-lines of the 570 km telephone line.[2] The EMP from the same test started a fire that burned down the Karaganda power plant, and shut down 1,000 km (620 mi) of shallow-buried power cables between Astana (then called Aqmola) and Almaty.[3]