The TISP70xxL1 series are 3-point overvoltage protectors designed for protecting against metallic (transverse mode) and simultaneous longitudinal (common mode) impulses. Each terminal pair has the same voltage limiting values and surge current capability. These devices are designed to limit overvoltages between signal, data and control port conductors, connected to terminals T1 and T2, and a protective ground, G. Each terminal pair has a symmetrical voltage-triggered bidirectional thyristor characteristic (Figure 1). 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 device holding current will normally be higher than the available short circuit d.c. system current, causing the protector to switch off as the diverted current subsides.