GDT
Gas-discharge protection tube
A gas-discharge tube provides a documented surge-protection path through gas breakdown.
SLD / Schematic
IEC · F
Symmetric gas discharge tube
A protective gas discharge tube drawn with identical electrodes either side, listed as a distinct symmetric form.
In plain English
What does Symmetric gas discharge tube mean?
The publisher's IEC-oriented library lists a symmetric protective gas discharge tube separately from the standard form. The symmetric drawing presents both electrodes identically, emphasising that the device behaves the same for either polarity of surge, as is typical for AC and signal line protection.
A simple example
The symbol is a drawing variant and does not establish electrical ratings. Breakdown voltage, impulse current and follow current behaviour come from the product data. Readers should not infer three-terminal construction from this form; three-electrode tubes need their own representation.
What the drawings help you do
Read ratings from the product data, not the symbol. Check whether a three-electrode tube is intended instead. The symmetric form draws identical electrodes; the standard gas discharge tube form may show the electrodes differently.
This particular reference
A protective gas discharge tube drawn with identical electrodes either side, listed as a distinct symmetric form. The symmetric form draws identical electrodes; the standard gas discharge tube form may show the electrodes differently.
- AC
- Alternating current: electricity whose direction changes periodically.
- Terminal
- An identified point where a conductor connects.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: AutoCAD Electrical: Earthing, sources and surge protection · IEC-60617 symbol preview directory
IEC · Protective Gas Discharge Tube, Symmetric
Autodesk IEC-60617 Symbol Preview: Miscellaneous; vendor family reference, not certified IEC geometry.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · F
What it represents
The publisher's IEC-oriented library lists a symmetric protective gas discharge tube separately from the standard form. The symmetric drawing presents both electrodes identically, emphasising that the device behaves the same for either polarity of surge, as is typical for AC and signal line protection.
The symbol is a drawing variant and does not establish electrical ratings. Breakdown voltage, impulse current and follow current behaviour come from the product data. Readers should not infer three-terminal construction from this form; three-electrode tubes need their own representation.
How to read it
- Read ratings from the product data, not the symbol.
- Check whether a three-electrode tube is intended instead.
Information to show or reference
- State sparkover voltage and impulse rating.
- Show the earth or return side.
- Keep the form consistent with the legend.
A distinction that matters
The symmetric form draws identical electrodes; the standard gas discharge tube form may show the electrodes differently.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Earthing, sources and surge protection
Public IEC-oriented preview listing the symmetric protective gas discharge tube form.
IEC-60617 symbol preview directory
Public directory of IEC-oriented symbol families.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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