Can't find anything on what the symbol inside of the red circle. Any identification of the symbol would be appreciated, bonus love for its functionality in this circuit as well!
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2The Q&A [Polarity of gas discharge tubes](https://electronics.stackexchange.com/q/455664/36731) has some information you might find interesting. – Andrew Morton Aug 18 '22 at 18:59
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Gas discharge tube. Very high current handling capability, but generally less precise breakdown voltage than semiconductor devices. Frequently used in conjunction with semiconductor devices to provide lightning strike protection.
vir
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What does this symbol mean in the internal circuitry of a surge protector device?
It's a spark-gap or gas discharge tube (GDT): -
Image from here
bonus love for its functionality in this circuit as well
If the voltage gets too high the GDT "fires" and clamps the applied voltage to a a few volts. It's not particularly fast in operation but, it can handle power surges that MOVs or semiconductor clampers can't. However, it's not so useful on a DC supply because once it activates, it will clamp the voltage ad infinitum whereas on AC, its cyclical nature means it can self-reset every half cycle.
Andy aka
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