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Gas Discharge Tube Testing

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gavin23

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Hello:

I've received back some units from the field that appear to have suffered huge surge currents (enough to burn traces of the PCB). There is a Gas Discharge Tube (GDT) on the unit for surge protection but it looks like it wasn't enough. The datasheet is attached, I have the 2026-23 version (230V).

My guesses are these:
1/ There were numerous surges, beyond what the GDT was rated for. As a result it failed and the next surge damaged the device.
2/ There was a massive surge that surpassed the maximum ratings of the GDT causing arcing and thus damage to the board.

I'm interested to know if the GDT is damaged. I'm going to test the GDT using a DC HiPot tester.

Any thoughts?

Thanks,
Gavin
 

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  • Bourns - 2026-XX Thru-Hole.pdf
    260.4 KB · Views: 17

FvM

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I can't comment your observations without knowing the circuit and the location of PCB damage. As the datasheet clarifies, a GDT can be expected to fail short (by evaporated electrode metal deposited at the ceramics). Of course, there's a certain current level where device will be completely blown, but most likely, the "upstream" PCB traces will be before.
 

gavin23

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Just to provide some more details:

The GDT I'm using doesn't fail short (ie I didn't order the fail-short option)

The GDT has 3 terminals. One (middle terminal) is connected to chassis ground. The other 2 are connected to tip and ring (this is a DSL communications line). After the GDT there is a common-mode choke followed by a DSL transformer.

From the looks of the damage the surge was either so great the Gas Tube alone couldn't handle it and it arced to the chassis connection. Or else, the Gas Tube was damaged (thus leaving no protection) and the surge arced. Everything behind the gas tube shows no damage. All charring is confined to the traces connecting the GDT and the chassis ground connection.
 

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Are you sure, that board wasn't simply damaged by overcurrent through the GDT?
 

gavin23

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If it was due to overcurrent through the GDT, wouldn't the GDT be damaged?
 

gavin23

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I tested the GDTs and they are still working.

I think I understand what you mean now. The GDT can handle a huge amount of current (ie 10kA) whereas the PCB traces cannot. In an extremely high-currents the GDT would survive and the PCB traces would end up getting burnt off.
 

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