A GDT is typically placed in the circuit to either divert surge energy to ground (common mode) or to a source (differential mode). The GDT has very high impedance (>1 Gohm) so it is virtually invisible to the circuit during normal operation. When a voltage disturbance reaches the GDT sparkover value, the GDT will switch into a virtual short circuit, known as the arc mode. In the arc mode, the GDT practically shorts the line, diverting the surge current through the GDT to ground or source and removes the voltage surge from the plant and equipment. At normal operating voltages below the GDT rated DC sparkover voltage, the GDT remains in a high impedance off-state condition. With an increase in voltage across its conductors, the GDT will enter into its glow voltage region. The glow region is where the gas in the tube starts to ionize due to the charge developed across it. While the GDT is in its glow region operation, the increase of current flow will create an avalanche effect in gas ionization that will transition the GDT into a virtually short circuit mode and current will pass between the two conductors. The voltage developed across the GDT with a short circuit condition is called the “Arc Voltage,” or V-ARC. The transition time between the glow and arc region is dependent on the available current of the impulse, the distance and shape of the electrodes, the gas composition, gas pressure and the proprietary emission coatings. Bourns active emission coatings allow the tubes to transition into the arc mode at currents much lower than 500 mA. The arc voltage is the voltage rating that is specified as <10 V @ 1 A for Bourns® GDTs. The GDT will switch back or reset into a high impedance state once there is not enough energy to keep the device in the arc condition. This is sometimes called the Extinguishing Voltage, Holdover Voltage or Impulse Reset Voltage.