These devices are designed to limit overvoltages between systems and so protect their insulation. A single device can be used in two ways; as a 3-point protector or as a 2-point protector. In the 3-point mode, the G terminal is connected to the system protective ground and the R and T terminals are connected to the two conductors being protected. For the TISP3600F3, each conductor will have its voltage limited to 600 V from the protective ground. The maximum inter-conductor voltage will be limited to 1200 V. In the 2-point mode, only the outer R and T terminals are connected and the G terminal is unconnected. The TISP3700F3 limits the voltage between the two connection nodes to 1400 V with voltage limiting beginning above 1000 V. Two TISP3700F3 devices connected in series would allow insulation testing to 2000 V ( 1400 Vrms ). The protector consists of two symmetrical voltage-triggered bidirectional thyristors with a common connection. Overvoltages are normally caused by a.c. power system or lightning flash disturbances which are coupled on to the system. These 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. The TISP3x00F3 is guaranteed to voltage limit and withstand the listed international lightning surges in both polarities.