{"schemaVersion":1,"slug":"iec-symmetric-gas-discharge-tube","name":"Symmetric gas discharge tube","kind":"symbol","abbreviation":"F","aliases":["symmetric GDT","symmetrical gas tube","bidirectional gas discharge protector"],"category":"connections-wiring","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"A protective gas discharge tube drawn with identical electrodes either side, listed as a distinct symmetric form.","description":["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."],"readingNotes":["Read ratings from the product data, not the symbol.","Check whether a three-electrode tube is intended instead."],"drawingChecklist":["State sparkover voltage and impulse rating.","Show the earth or return side.","Keep the form consistent with the legend."],"distinction":"The symmetric form draws identical electrodes; the standard gas discharge tube form may show the electrodes differently.","facts":[{"label":"Graphic cue","value":"Sealed envelope with matching electrodes either side"},{"label":"Publisher form","value":"Protective Gas Discharge Tube, Symmetric (HFU1_S00375 Autodesk identifier)"},{"label":"Preview","value":"Original educational illustration; consult the publisher and applicable standard for the exact graphic"}],"references":[{"sourceId":"pub-symbol-earthing-surge","relevance":"Public IEC-oriented preview listing the symmetric protective gas discharge tube form."},{"sourceId":"autodesk-index","relevance":"Public directory of IEC-oriented symbol families."}],"related":["gas-discharge-protection-tube","ansi-gas-discharge-tube","iec-double-spark-gap"],"artwork":"s28-iec-symmetric-gas-discharge-tube","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","symbolVariant":{"convention":"IEC","form":"Protective Gas Discharge Tube, Symmetric","reference":"Autodesk IEC-60617 Symbol Preview: Miscellaneous; vendor family reference, not certified IEC geometry.","counterpart":"gas-discharge-protection-tube"},"plainEnglish":{"title":"What does Symmetric gas discharge tube mean?","introduction":"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.","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.","drawings":"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.","terms":[{"name":"AC","meaning":"Alternating current: electricity whose direction changes periodically."},{"name":"Terminal","meaning":"An identified point where a conductor connects."},{"name":"Signal","meaning":"Electrical information passed between devices, rather than necessarily the main power supply."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"AutoCAD Electrical: Earthing, sources and surge protection","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-1E3FDEAE-B4B2-417C-8075-108AA2C6E509.htm"},{"label":"IEC-60617 symbol preview directory","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-7871E6EF-24D5-467E-9B74-321FEDC9DFDA.htm"}],"detail":"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.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/iec-symmetric-gas-discharge-tube","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/iec-symmetric-gas-discharge-tube.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-symbol-earthing-surge","title":"AutoCAD Electrical: Earthing, sources and surge protection","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-1E3FDEAE-B4B2-417C-8075-108AA2C6E509.htm","type":"cad-reference","scope":"Public vendor catalogue naming and functional variants. Vendor block names are not IEC identifiers. Linked for reference; no graphics or CAD files are redistributed.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public IEC-oriented preview listing the symmetric protective gas discharge tube form."},{"id":"autodesk-index","title":"IEC-60617 symbol preview directory","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-7871E6EF-24D5-467E-9B74-321FEDC9DFDA.htm","type":"cad-reference","scope":"Public reference directory of named symbol categories. Vendor graphics and CAD library files are not redistributed here.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public directory of IEC-oriented symbol families."}]}