# ANSI/IEEE on-delay normally-open contact symbol

Canonical URL: https://eloragrid.ai/symbols/ansi-on-delay-normally-open-contact
Publisher: Elora Grid
Updated: 2026-10-14
Lookup label: TON NO
Drawing use: Schematic
Reference families: IEEE / ANSI, Manufacturer

## Symbol convention

Convention: IEEE / ANSI
Form: Autodesk IEEE-oriented Time Delay Relays functional form
Autodesk explicitly publishes this block under IEEE Symbol Preview. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted.
Related representation: [On-delay normally-open contact](https://eloragrid.ai/symbols/on-delay-normally-open-contact)

IEEE-oriented graphical reference for on-delay normally-open contact, with public vendor evidence and drawing-reading notes.

## What it represents

The on-delay NO contact form specifically describes a delayed-closing transition. Its timer reference supplies the initiating condition and interval, while the unoperated contact remains open; release or reset behaviour comes from the documented timing chart.
This is a convention-specific lookup based on the publisher's IEEE-labelled preview. The geometry here is independently drawn to explain the connection or operation; it is not a certified reproduction of the standard graphic.

## How to read it

- Separate the delay-close transition from the contact's return action.
- Read the selected library and the project legend together. A vendor block identifier is meaningful within its named library and is not a universal standard-symbol code.

## Information to show or reference

- Link timer element
- State closing delay
- Reference reset behaviour

## Important distinction

A timed output contact differs from the timer coil or trigger that initiates its timing.

## Facts

- Convention evidence: Autodesk IEEE Symbol Preview — Time Delay Relays
- Public vendor block name: HTD21N (Autodesk identifier; not an IEEE symbol number)
- Standards context: IEEE/ANSI 315-1975 covers diagram graphics. IEEE lists this edition as Inactive-Reserved.
- Artwork scope: Original functional illustration; exact standard glyph and compliance are not certified

## Public references

- [Autodesk IEEE Symbol Preview — Time Delay Relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-BBFF0443-6EA2-4A05-A761-F411E16BA070.htm) — Autodesk. Exact public IEEE-oriented category page verifying the component name and vendor block identifier.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. Graphic-symbol standards context and official status; not a source of reproduced artwork.

## 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.