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 . AC powered equipment and critical 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.

AC Main Port Protection for Type A Equipment

IEC 62368-1 provides component requirements of Metal Oxide Varistors and Gas Discharge Tubes (GDT) when they are used to protect pluggable Type A equipment mains ports. IEC 62368-1 classifies pluggable Type A equipment as potentially having an unreliable earth-ground bonding. To safeguard against the failure of any mains port MOV connected between line and PE, a GDT is required to be connected in series with those MOV components. The circuit diagram below illustrates the Gas Tube requirement for isolating line connected MOV components from PE. Please consult the latest edition of IEC 62368-1 for the full range of requirements related to MOV and GDT used in mains port protection for Type 2 equipment.

Line Isolating GasTube

Selecting the appropriate Gas Tube

IEC 626380-1 category II generally covers equipment designs based on 120V or 230V AC mains. As defined in the requirement, 230VAC equipment must have a minimum transient peak voltage withstand levels of 2.5kV. The GDT listed below is recommended for 120V Type 2 pluggable AC equipment requiring no conduction at a nominal 2.5 kV dc or 1.77 kV AC rms.

Recommended GDT

Part NumberCircuitDC Sparkover VoltageInLink
BH S 3500/15230VAC3500 +/-15%10kA


1ITU K.12, Characteristics of gas discharge tubes for the protection of telecommunications installations
2UL497B, Surge Protectors for Data Lines and Fire-Alarm Circuits
3IEC 62368-1, AC Mains Port Protection Component Requirements

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