The TISP3xxxH3SL limits overvoltages between the telephone line Ring and Tip conductors and Ground. Overvoltages are normally caused by a.c. power system or lightning flash disturbances which are induced or conducted on to the telephone line. The protector consists of two symmetrical voltage-triggered bidirectional thyristors. Overvoltages are initially clipped by breakdown clamping until the voltage rises to the breakover level, which causes the device to crowbar into a low-voltage on state. This low-voltage on state causes the current resulting from the overvoltage to be safely diverted through the device. The high crowbar holding current prevents d.c. latchup as the diverted current subsides. This TISP3xxxH3SL range consists of eleven voltage variants to meet various maximum system voltage levels (58 V to 275 V). They are guaranteed to voltage limit and withstand the listed international lightning surges in both polarities. These high current protection devices are in a 3-pin single-in-line (SL) plastic package and are supplied in tube pack. For alternative impulse rating, voltage and holding current values in SL packaged protectors, consult the factory. For lower rated impulse currents in the SL package, the 35 A 10/1000 TISP3xxxF3SL series is available. These monolithic protection devices are fabricated in ion-implanted planar structures to ensure precise and matched breakover control and are virtually transparent to the system in normal operation.