Trying to determine what this small glass-enclosed item is

Question

I need help identifying the small, glass-enclosed device shown below. Printed circuit board has DSA1 printed near it. A wider view of the PCB is also attached. The item I am asking about is in the upper right of the broader photo.

Thanks, David

Edit: Thanks, Winny, All! I have added 3 more images, 2 of which are backlit. The lug on the in the upper right of the front side accepts the black wire from the power (line) source, and the lug on the back of the board accepts a green (ground) wire from the motor (this is a pool pump motor). While looking into this I remembered that I never did connect a bonding wire that runs between a clamped connection on the outside of the motor housing and to a metal part of the pool. I will investigate further to see if the green wire that disappears into the pump motor housing actually connects to that outside clamp connector. Is there a way to test the discharge device? Should it have continuity across the ends?

EDIT 2: I accidentally erased the post identifying the device as a Glass Discharge Tube (Surge protector). Sorry!

Answer 1

It's a gas discharge tube. Used for e.g. lightning surge protection.

They are sealed tubes of noble gas which are designed become conductive when a high voltage spike occurs. The GDT then provides a short circuit to dissipate the energy of the spark and hopefully protect the rest of the circuit.

Answer 2

Context from the surrounding circuit is worth looking at:

CN1 (fused, 'L') and CN2 ('H') are single-phase connections to the line filter (yellow 'X' type capacitors, common-mode chokes) and remaining power circuitry (out of frame). The blue things RV1-3 are varistors (MOVs), in a triangle. This is a common motif to limit both line-to-line and line-to-ground voltage.

^{simulate this circuit – Schematic created using CircuitLab}

There's a catch: as MOVs fail from repeated surge events, leakage current generally increases; or the capacitance alone leaks enough current at mains frequency anyway. Whatever the case, tying them to ground directly could be a problem: whether because ground may come loose and exposes the user to hazardous leakage current, or because the MOVs fail completely and short mains to GND (including if N (unfused!) is hot, which can happen with improper wiring, 3ph line-to-line circuits, or typical 240V circuits in North America).

The preferred solution is to connect something in series, that has a high impedance at normal mains voltages, but which breaks down at surge voltages. A GDT (gas discharge tube) is an appropriate choice here.

This brings the surge protection network into compliance with standards such as IEC 62368-1 §5.5.7.

Answer 3

It's a gas discharge tube arrester for circuit protection against surge voltages.

Image credit: DigiKey / Mitsubishi

Here's another, from a Mitsubishi TV board, that is closer in looks to the item in question.