The Insurance Institute for Business & Home Safety found that an estimated $26B dollars annually is lost due to non-lightning power surges. Additionally, the are an estimated 25 million lighting strikes in the US each year that cause between $650M to $1B in losses according to the Insurance Institute, State Farm . Ethernet equipment interfaces and critical communication infrastructure must be protected from threats due to lighting, power surges and power induction.

How Gas Tubes Operate

Gas Discharge Tube (GDT) Surge Arrestors operate on the principle of arc discharge. Operating as a voltage-dependent switch, an arc is formed within nano-seconds inside the hermetically sealed discharge chamber once a voltage exceeds the GDTs spark-over voltage. During its on-state, the gas tube essentially forms a short circuit allowing the entire surge current to flow and instantaneously eliminating the overvoltage transient. Upon dissipation of the overvoltage event, the GDT device extinguishes and the internal resistance returns to its high impedance off-state. GDT devices reliably limit over voltages to permissible levels, can handle large surge currents and are invisible to the system being protected due to low capacitance and very high insulation resistance.

Ethernet Interface Protection

GDT are an ideal solution for overvoltage protection of data interfaces due to their small size, high current capacity, high insulation resistance and low capacitance. Typical Ethernet interface applications include routers, switches, patch panels, modules, set-top boxes, CCTV and WLAN-AP.

Gas Tube Protecting Ethernet Interface

Selecting the appropriate Gas Tube

Key considerations for selection of a GDT for Ethernet equipment include location, system voltages, package types and surge ratings. Powered Ethernet (POE) systems typically operate in a range from 48Vdc to 65Vdc. When selecting a GDT, the minimum DC breakdown of the GDT must be considered. A 90V GDT with a 20% tolerance has a minimum DC breakdown voltage of 72V which is above the maximum 65Vdc system voltage for a typical POE system. For the majority of Ethernet interfaces, a 90V gas tube is an ideal choice for overvoltage protection. A 5mm surface mount GDT with a maximum rating of 5kA would be a typical choice for equipment deployed inside a building. For equipment deployed in harsher environments, 8mm GDT are available with surge current ratings of 10kA up to 20kA.

Recommended GDT

Part NumberCircuitDC Sparkover VoltageInLink
BASQ CMS 90/20POE up to 65Vdc90 +/-20%5kA


1ITU K.12, Characteristics of gas discharge tubes for the protection of telecommunications installations
2UL497B, Surge Protectors for Data Lines and Fire-Alarm Circuits
3GR-1089-CORE, Electomagnetic Compatibility and Safety
4ITU K.21, Resistibility of telecommunication equipment installed in customer premises to overvoltages and overcurrents

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