Gas discharge tubes are crowbar devices — when the voltage across them exceeds the sparkover threshold, they conduct hard and clamp the line close to arc voltage (typically 10–20V). That makes them fundamentally different from TVS diodes, which clamp at a defined voltage but remain in the circuit. Once a GDT fires, it stays conducting until current falls below the holding threshold.

Their main advantage over TVS diodes is capacitance. A GDT sits below 1pF at signal frequencies, while a TVS diode can range from tens to hundreds of pF. For telecom lines, RS-485, and high-speed data interfaces, that capacitance difference is significant. GDTs also handle high surge energy — the kind generated by indirect lightning strikes — in a very small package.

Specifying correctly means understanding two sparkover figures. DC sparkover is the static threshold measured with a slow voltage ramp. Impulse sparkover (measured at 100V/µs or 1000V/µs rise rates) is always higher because ionisation takes time — the gas hasn't had a chance to break down when the voltage spike arrives. For lightning protection, the impulse figure is what matters for your protection coordination calculation.

TRX sources gas discharge tubes from Bourns, Littelfuse, and Epcos (TDK) through authorised distribution, with stock available across Johannesburg, Cape Town, Durban, and Pretoria. No minimum order.

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