The timer relay symbol on a schematic tells you exactly how a circuit handles time-based switching—whether it delays turning on, delays turning off, or pulses. Because North American (ANSI/IEEE) and International (IEC) drafting standards use entirely different graphical languages, misreading a single arrow or dashed line can wire a machine to start prematurely or fail to safety-interlock. Below is the complete reference for identifying, wiring, and verifying timer relays on the bench or in the panel, starting with the core function table.
Complete Timer Relay Symbol & Function Reference
The following table maps the four primary time-delay functions to their respective IEC 60617 and ANSI/IEEE 315 schematic symbols, alongside the standard physical pinout for the ubiquitous 8-pin octal base (e.g., Omron PYF08A socket). Use this as your primary cross-reference when reading prints from international OEMs or legacy domestic panels.
| Function Type | IEC 60617 Symbol Marker | ANSI/IEEE 315 Symbol Marker | 8-Pin Octal Base Wiring | Practical Application |
|---|---|---|---|---|
| On-Delay (TON) | Rectangle envelope with an inward-pointing arrow on the contact arm (slow to operate). | Coil circle marked 'TD' or 'TON'; contact arm features a curved dashed line pointing away from the pivot. | Coil: Pins 2 & 7. NO Contacts (3 & 6) delay closing after coil energization. NC (4 & 5) delay opening. | Motor star-delta transition; delaying a conveyor start until a crusher reaches full RPM. |
| Off-Delay (TOF) | Rectangle envelope with an outward-pointing arrow on the contact arm (slow to release). | Coil circle marked 'TOF'; contact arm features a curved dashed line pointing toward the pivot. | Coil: Pins 2 & 7. NO Contacts (3 & 6) remain closed for the set duration after coil de-energization. | Cooling fan run-on after a VFD or main drive motor stops; alarm horn silencing delays. |
| Interval (One-Shot) | Rectangle with a bidirectional arrow or specific internal pulse marker (often an 'X' or clock). | Coil marked 'OS' or '1S'; contact shows a standard throw with a specialized pulse indicator. | Coil: Pins 2 & 7. NO (3 & 6) closes for a fixed, pre-set time immediately upon coil trigger, regardless of how long the trigger is held. | Packaging dosing valves; conveyor belt jog functions; garage door opener pulse simulation. |
| Repeat Cycle (Flasher) | Rectangle with a continuous wave or alternating pulse marker inside the envelope. | Coil marked 'RPT' or 'FLS'; contacts show alternating arrows or a zig-zag delay line. | Coil: Pins 2 & 7. NO and NC contacts alternate states continuously at the dialed-in frequency as long as power is applied. | Warning beacon flashing; automated lube pump cycling; greenhouse misting systems. |
Regional Standards: IEC vs. ANSI and Faded Markings
Knowing which standard applies to your region—and more importantly, which standard the original equipment manufacturer (OEM) used—is critical for safe interpretation. According to the IEC Standard Symbol Database, international schematics rely heavily on rectangular envelopes. The internal geometric markers (like the direction of the arrow relative to the contact line) dictate the timing behavior. In contrast, North American schematics governed by NEMA and ANSI/IEEE standards rely on device function numbers (such as ANSI device number 2 for Time Delay Starting, and 62 for Time Delay Stopping) and specific curved/dashed lines drawn directly on the contact arms.
If the physical relay label (e.g., on an Omron H3Y-2 or Finder 80.11 multifunction module) is worn off, melted, or missing, do not guess the timing function based on the base pinout alone. The 8-pin socket dictates only the physical connections (coil vs. contacts), not the internal logic. An off-delay relay and an on-delay relay will plug into the exact same PYF08A socket and show identical continuity on the bench when unpowered. You must apply control voltage and map the timing behavior with a stopwatch before wiring it into a live safety circuit.
When interpreting older UK or pre-IEC harmonized European drawings, you may encounter legacy symbols that use a simple clock face icon inside the coil circle without directional arrows. In these ambiguous cases, treat the symbol as an On-Delay (TON) by default, as it was the historical standard, but verify on the bench. For a deeper dive into legacy and modern contact representations, the All About Circuits Relay Symbols Reference provides excellent visual comparisons of these transitional drafting eras.
The "Rows People Get Wrong" Notes
Even experienced panel builders make specific errors when translating these symbols into physical wiring. Here are the most common pitfalls and how to avoid them:
- Confusing the IEC Delay Arrow Direction: In IEC 60617, an arrow pointing towards the contact line means On-Delay (slow to operate). An arrow pointing away from the contact line means Off-Delay (slow to release). A common field mistake is wiring a panel cooling fan to an On-Delay timer because the builder misread the arrow, resulting in the fan starting late rather than running long after the heat source shuts off.
- The "Pin 2 and 7" Assumption on 11-Pin Bases: The reference table above uses the standard 8-pin octal layout. If you are using an 11-pin undecal base (like the Omron PYF11A), the coil pins shift. On most 11-pin timer relays, the coil is wired to pins 2 and 10, while pin 7 acts as a common or secondary coil pin for dual-voltage models. Always check the specific manufacturer datasheet printed on the side of the relay housing.
- Treating Solid-State Timers Like Electromechanical: Solid-state timer modules (such as the Macromatic TR-65 series) often use schematic symbols that look identical to electromechanical relays. However, their "coil" pins are actually low-voltage DC control inputs, and their "contacts" are triac or MOSFET outputs. Wiring 120VAC to the control input pins of a solid-state timer will instantly destroy the internal optocoupler and short the output.
- Ignoring the "Retrigger" Behavior in One-Shots: The Interval (One-Shot) symbol implies a fixed output pulse. However, builders often fail to check whether the specific relay model is "retriggerable." If a retriggerable one-shot receives a second trigger pulse before its timing cycle finishes, the timer resets to zero and starts over. If your application requires a strict, non-extendable pulse regardless of input bouncing, you must specify a non-retriggerable module.
Safe Interpretation and Bench Verification
When you are handed a replacement timer relay with no documentation, or when a schematic is too damaged to read the symbol clearly, you must trace the device empirically. Follow this bench verification sequence to map the relay safely.
- Identify the Coil Pins (Resistance Test): Set your multimeter to resistance (Ohms). Probe the base pins. On an 8-pin base, look for a reading between 50Ω and 10kΩ across pins 2 and 7 (depending on whether it is a 24VDC, 120VAC, or 240VAC coil). All other pin combinations should read infinite (OL) or show standard contact continuity.
- Map the Contact Logic (Continuity Test): With the relay unpowered, use the multimeter's continuity/diode beep mode. Probe pins 1, 3, and 4. Pin 1 to Pin 4 should read less than 1 ohm (Normally Closed). Pin 1 to Pin 3 should read infinite/OL (Normally Open). Repeat for the second pole (Pins 8, 5, and 6).
- Power and Time the Logic: Mount the relay in a socket connected to a bench power supply or an isolated control transformer. Never test an unknown relay by plugging it directly into a live 480V panel. Apply the rated coil voltage (e.g., 24VDC). Use a stopwatch to measure the exact delay from the moment voltage is applied to the moment the NO contacts close (audible click or multimeter beep).
- Test the Drop-Out Delay: Remove power from the coil and immediately start the stopwatch. Measure how long it takes for the contacts to return to their unpowered state. If it drops out instantly but delayed on power-up, you have an On-Delay (TON). If it drops out after a delay, you have an Off-Delay (TOF).
By combining a strict reading of the schematic symbols with empirical bench verification, you eliminate the guesswork that leads to miswired safety interlocks and nuisance machine faults. Always default to the physical datasheet and bench testing when the ink on the schematic—or the relay itself—starts to fade.
