{"schemaVersion":1,"slug":"iec-timing-relay-form-normally-open-delay-on-off","name":"IEC timing-relay form: normally open delay on/off","kind":"symbol","abbreviation":"KT","aliases":["HTD21DOO","VTD21DOO","timing-relay form Normally Open Delay ON/OFF"],"category":"control-circuits","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Timing-relay form form: Normally Open Delay ON/OFF.","description":["A timing relay separates the initiating signal from the later change of an output contact. The contact state, delayed transition and reset condition are independent: a timer may have immediate contacts alongside delayed contacts under the same device tag. This entry identifies the normally open delay on/off form in the publisher's IEC-context family.","A control sequence may start an auxiliary before enabling the main load, or keep a fan running after a stop request. Trace supply, trigger and output separately, then draw a timing chart that includes what happens when the trigger ends before a delay has elapsed. The normally-open designation starts with a non-conducting output or open contact in the documented reference condition; operation changes that state.","The symbol does not supply the time setting, retriggering rule or power-loss behaviour. A three-terminal timing form also needs its actual manufacturer terminal mapping; the vendor name alone does not define a universal pinout."],"readingNotes":["The normally-open designation starts with a non-conducting output or open contact in the documented reference condition; operation changes that state.","The symbol does not supply the time setting, retriggering rule or power-loss behaviour. A three-terminal timing form also needs its actual manufacturer terminal mapping; the vendor name alone does not define a universal pinout."],"drawingChecklist":["Identify the initiating supply or control signal.","Label delayed and immediate output transitions separately.","Reference timing settings, reset conditions and the device timing chart."],"distinction":"This entry adds the normally open delay on/off detail to the broader timing-relay form family. The symbol does not supply the time setting, retriggering rule or power-loss behaviour. A three-terminal timing form also needs its actual manufacturer terminal mapping; the vendor name alone does not define a universal pinout.","facts":[{"label":"Drawing form","value":"Normally Open Delay ON/OFF"},{"label":"Public vendor block names","value":"HTD21DOO / VTD21DOO. Autodesk identifiers, not standards database IDs."},{"label":"Drawing purpose","value":"timing-relay form"},{"label":"Graphic scope","value":"Independently authored educational illustration; not certified standard geometry, a terminal pinout or a product footprint."}],"references":[{"sourceId":"pub-symbol-timers","relevance":"Public Time Delay Relays table explicitly lists HTD21DOO / VTD21DOO with this operating or connection form. Vendor graphics are linked, not copied."}],"related":["on-delay-timer-relay","off-delay-timer-relay","relay-coil"],"artwork":"s28-iec-timing-relay-form-normally-open-delay-on-off","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","symbolVariant":{"convention":"IEC","form":"Normally Open Delay ON/OFF","reference":"Autodesk IEC-60617 Symbol Preview: Time Delay Relays, HTD21DOO / VTD21DOO. This identifies the publisher's library context; exact IEC graphics and database identities are not asserted."},"plainEnglish":{"title":"What does IEC timing-relay form: normally open delay on/off mean?","introduction":"A timing relay separates the initiating signal from the later change of an output contact. The contact state, delayed transition and reset condition are independent: a timer may have immediate contacts alongside delayed contacts under the same device tag. This entry identifies the normally open delay on/off form in the publisher's IEC-context family.","example":"A control sequence may start an auxiliary before enabling the main load, or keep a fan running after a stop request. Trace supply, trigger and output separately, then draw a timing chart that includes what happens when the trigger ends before a delay has elapsed. The normally-open designation starts with a non-conducting output or open contact in the documented reference condition; operation changes that state.","drawings":"The symbol does not supply the time setting, retriggering rule or power-loss behaviour. A three-terminal timing form also needs its actual manufacturer terminal mapping; the vendor name alone does not define a universal pinout.","terms":[{"name":"Normally open / normally closed","meaning":"The contact state in the normal condition defined for the drawing."},{"name":"Coil","meaning":"A wound conductor that can produce a magnetic field when energised."},{"name":"Terminal","meaning":"An identified point where a conductor connects."}],"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: Time-delay relays","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-DA927086-EEAF-48CB-B9B1-634A4B48C8C7.htm"}],"detail":"Timing-relay form form: Normally Open Delay ON/OFF. This entry adds the normally open delay on/off detail to the broader timing-relay form family. The symbol does not supply the time setting, retriggering rule or power-loss behaviour. A three-terminal timing form also needs its actual manufacturer terminal mapping; the vendor name alone does not define a universal pinout.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/iec-timing-relay-form-normally-open-delay-on-off","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/iec-timing-relay-form-normally-open-delay-on-off.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-timers","title":"AutoCAD Electrical: Time-delay relays","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-DA927086-EEAF-48CB-B9B1-634A4B48C8C7.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 Time Delay Relays table explicitly lists HTD21DOO / VTD21DOO with this operating or connection form. Vendor graphics are linked, not copied."}]}