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I can see that G represents a generator/oscillator, and T represents a Transformer, but what does GT represent?

  • \$\begingroup\$ An oscillating transformer?: I can see that you can't see that we can't see what you're talking about without some more information. How about editing your question so we won't have to guess/close your question? \$\endgroup\$ – EM Fields Jan 13 '16 at 13:54
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    \$\begingroup\$ It could be something like a gas discharge tube, but it's hard to guess. Do you have a picture of the component? \$\endgroup\$ – Armandas Jan 13 '16 at 13:55
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    \$\begingroup\$ "Gas Tube" -- it's an overvoltage protection device. \$\endgroup\$ – Dave Tweed Jan 13 '16 at 14:05
  • \$\begingroup\$ Designators can be somewhat arbitary. There are conventions for the common stuff but when one has an unusual component a designer will often end up making it up as they go along. \$\endgroup\$ – Peter Green Jan 13 '16 at 15:16
  • \$\begingroup\$ @Roy If my answer helped you, please consider accepting it. Thanks. \$\endgroup\$ – Armandas Jan 15 '16 at 18:16

enter image description here

As I guessed in my comment, it's a Gas Discharge Tube. As Dave Tweed says, it's an overvoltage protection device, or more precisely, it protects against high voltage spikes as opposed to long term faults.

Here's an excerpt from a Littlefuse datasheet:

GDTs function as switches which dissipate a minimum amount of energy and therefore handle currents that far surpass other types of transient voltage protection. Their gas-filled, rugged ceramic metal construction make them well suited to adverse environments.

  • \$\begingroup\$ is there any device the protects against long-term faults? \$\endgroup\$ – Jasen Dec 18 '16 at 10:56
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    \$\begingroup\$ @Jasen For long term overvoltage protection, you typically need a circuit, rather than a single device. Though, depending on the applicaion, a PTC can sometimes be used. \$\endgroup\$ – Armandas Dec 18 '16 at 11:17

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