The symbol for time delay relay on a schematic changes based on two variables: the timing function (on-delay, off-delay, interval) and the regional drafting standard (IEC vs. NEMA). Misreading the bowtie, arrow direction, or contact state will wire your motor starter backwards and potentially drop a live load prematurely. Below is the exact reference data to decode your prints, bench-test unknown modules, and select the correct replacement.
The Complete Time Delay Relay Symbol Reference Table
Use this spec-sheet-table to match the graphic on your electrical print to the physical relay function. The 'Unpowered State' column tells you what the contacts do before any coil voltage is applied.
| Function | IEC 60617 Symbol Marker | NEMA / JIC Symbol Marker | Unpowered State | Practical Application |
|---|---|---|---|---|
| On-Delay (DOE) | Rectangle with 'E' or 'x' on NO contact | Bowtie with arrow pointing AWAY from contact | Open (NO) | Soft-starting conveyors, staggering compressor loads |
| Off-Delay (DODE) | Rectangle with 'R' or 'x' on NC contact | Bowtie with arrow pointing TOWARD contact | Closed (NC) | Run-on cooling fans, lube pumps after spindle stops |
| Interval (One-Shot) | Rectangle with 'I' or 'sa' | Bowtie with arrow pointing AWAY + small latch mark | Open (NO) | Garage door timers, automated misting cycles |
| Repeat Cycle (Flicker) | Rectangle with 'Rp' or dual arrows | Two bowties or wave-line inside standard coil | Open (NO) | Flashing beacons, chemical dosing pumps |
| True Off-Delay | Rectangle with 'Rt' (requires continuous power) | Bowtie pointing TOWARD + 'P' for power monitor | Closed (NC) | Emergency lighting, valve closure on main power loss |
Regional Standards: IEC 60617 vs. NEMA/JIC vs. Old UK
Drafting standards dictate how the relay coil and its timed contacts are drawn. Mixing these up on a custom control panel leads to failed inspections and confused maintenance techs.
| Standard | Coil Representation | Contact Timing Marker | Where It Applies |
|---|---|---|---|
| IEC 60617 | Rectangle with function letter inside (e.g., K1-E) | An 'x' drawn on the contact line, or specific letter codes (E=On, R=Off) | EU, Asia, modern global OEMs |
| NEMA ICS 2 / JIC | Circle or rectangle, labeled CR or TR | The 'bowtie' (two triangles) with a directional arrow on the contact arm | North America, heavy industrial |
| Old UK (BS 3939) | Circle with crosshatch | Delayed action indicated by a small 'clock' arc or slash on the contact | Obsolete, found in pre-1990s UK plants |
The 'Rows People Get Wrong' Notes
When reading the symbol for time delay relay functions, three specific rows in the reference table above cause 90% of wiring errors on the bench.
- Off-Delay vs. True Off-Delay: A standard Off-Delay (DODE) requires a trigger signal to start. When the trigger drops, the timer counts down. A True Off-Delay monitors the main power line continuously; it does not need a separate trigger switch. If your schematic calls for a fan to run for 5 minutes after a total plant blackout, you must use a True Off-Delay, not a standard DODE.
- Interval (One-Shot) Re-triggering: The Interval symbol implies the relay closes for a set time the moment the trigger is applied. People wrongly assume that holding the trigger button will keep resetting the timer. It will not. The relay ignores subsequent triggers until the initial cycle finishes and the input drops to zero.
- The 'Not' Contact (NC vs NO): On NEMA prints, if the bowtie and arrow are drawn on a Normally Closed (NC) contact, it means the contact opens instantly on trigger, and delays returning to the closed state when the trigger is removed. Always trace the arrow to see which direction the delay applies.
Decision Tree: Picking the Right TDR Function and Part
Use this decision-tree-table to translate your operational requirement into a specific relay function, terminating in a concrete hardware selection.
| Operational Need (If...) | Required Function (Then...) | Concrete Hardware Pick |
|---|---|---|
| Motor must wait 10s after start button is pressed to avoid inrush spikes | On-Delay (DOE) | Omron H3Y-2 AC120 (Fixed 10s) |
| Cooling fan must run 5m after the main spindle contactor drops out | Off-Delay (DODE) | Macromatic TR-63122 (Off-Delay specific) |
| Dosing pump must run for exactly 30s every time a float switch bobs, ignoring chatter | Interval (One-Shot) | Schneider Electric 8501-KPR12V20 |
| You are replacing a faded legacy relay and don't know the exact original function | Multi-Function (Selectable) | Default Pick: Macromatic TR-601 |
Safe Interpretation When Markings Are Faded or Missing
If you pull an 8-pin or 11-pin octal relay from a panel and the silk-screened symbol on the side is obliterated by oil and heat, do not guess. Bench-test it using a multimeter and a known power source.
Standard Pinout Baselines:
- 8-Pin Octal: Pins 2 and 7 are the coil. Pins 1 and 8 are the Common (C) contacts. Pins 3 & 6 are Normally Closed (NC). Pins 4 & 5 are Normally Open (NO).
- 11-Pin Octal: Pins 2 and 10 are the coil. Pins 1, 6, and 11 are Common. The remaining pins split between NC and NO sets.
The Bench Verification Procedure:
- Set your digital multimeter to Continuity (beep) mode.
- Place probes on the Common and NO pins (e.g., 1 and 5 on an 8-pin). It should read open (OL).
- Apply the rated coil voltage (check the tiny stamped text on the coil housing, usually 120VAC or 24VDC) to pins 2 and 7. Never apply voltage to the contact pins.
- Watch the DMM. If it beeps instantly, you have a standard instantaneous relay. If it beeps after 3-5 seconds, it is an On-Delay.
- Remove coil power. If the DMM stops beeping instantly, it confirms On-Delay. If it continues beeping for several seconds before dropping out, you have an Off-Delay relay.
For authoritative schematic references and standard definitions, consult the Electronics Tutorials guide on Timer Relays or review the function dip-switch matrices in the Omron H3Y series datasheets. Always verify your final wiring against the specific manufacturer's pinout diagram, as Chinese clone brands frequently swap the NO/NC pin positions on 11-pin bases.
