27. GDT Operation & Characteristics

Question.6

A GDT is installed on a 230VAC mains line for lightning surge protection.
A lightning surge fires the GDT. The surge passes in milliseconds.
But the GDT does not return to its off-state — it continues conducting, drawing large mains current until the upstream fuse blows.
What caused this?

The GDT was defective — it should always reset after a surge
The lightning surge permanently damaged the GDT
The mains voltage (230V) is above the GDT's arc voltage (~20V), so mains current sustains the arc
The GDT's DC sparkover voltage was too high

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