# IEC NOR gate (rectangular form) Canonical URL: https://eloragrid.ai/symbols/iec-nor-gate Publisher: Elora Grid Updated: 2026-10-28 Lookup label: ≥1 Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: ≥1 rectangular element with output negation circle Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted. Related representation: [NOR gate](https://eloragrid.ai/symbols/logic-nor-gate) IEC ≥1 element with a negated output; the output is active only when none of the inputs are active. ## In plain English ### What does IEC NOR gate (rectangular form) mean? The IEC NOR element is drawn as the ≥1 OR box with a negation circle at the output. Its output is at the external 1 state only when every input is inactive, which makes it a natural way to show an all-healthy or all-clear permissive on a logic sheet. ### A simple example Interlock diagrams sometimes use the NOR element to produce a ready signal from a list of blocking conditions. The reader should check whether the blocking inputs are themselves negated, because a double negation can turn the function back into an AND of healthy signals. ### What the drawings help you do As with all combinative IEC elements, the drawing says nothing about the response time or the electrical output stage. A NOR used in a safety function must also be traced to its implementing device to confirm the safety rating. ### This particular reference IEC ≥1 element with a negated output; the output is active only when none of the inputs are active. A ≥1 element without the output circle is a plain OR; the circle is the only difference. ### Terms - Signal: Electrical information passed between devices, rather than necessarily the main power supply. - Rating: A value stating the conditions for which equipment is specified. - Schematic: A drawing showing function and connections rather than physical appearance. Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram. - [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) - [SN74HC02 — NOR gate logic](https://www.ti.com/lit/ds/symlink/sn74hc02.pdf) ## What it represents The IEC NOR element is drawn as the ≥1 OR box with a negation circle at the output. Its output is at the external 1 state only when every input is inactive, which makes it a natural way to show an all-healthy or all-clear permissive on a logic sheet. Interlock diagrams sometimes use the NOR element to produce a ready signal from a list of blocking conditions. The reader should check whether the blocking inputs are themselves negated, because a double negation can turn the function back into an AND of healthy signals. As with all combinative IEC elements, the drawing says nothing about the response time or the electrical output stage. A NOR used in a safety function must also be traced to its implementing device to confirm the safety rating. ## How to read it - Count negations along the path; NOR with negated inputs is an AND of the uncomplemented signals. - Confirm which external level corresponds to the active state. ## Information to show or reference - Place the negation mark at the output edge. - Label each blocking input. - Reference the implementing hardware or program block. ## Important distinction A ≥1 element without the output circle is a plain OR; the circle is the only difference. ## Facts - Qualifier: ≥1 plus output negation - Common reading: Output active when all inputs inactive - Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic ## Public references - [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Rectangular OR qualifier and output negation. - [SN74HC02 — NOR gate logic](https://www.ti.com/lit/ds/symlink/sn74hc02.pdf) — Texas Instruments. Manufacturer NOR gate documentation. ## Graphic scope Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.