Time Delay Relays: Types, Functions & Applications

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A time delay relay changes a control output according to two conditions: an input event and a time rule. Depending on the selected function, it can delay a start, delay a stop, create a fixed-duration pulse, repeat an ON/OFF cycle, or coordinate a star-delta transition.

The most reliable way to choose one is to define the required output timeline first. Then verify the trigger method, reset and power-loss behavior, supply voltage, output contact duty, and mounting against the exact model datasheet. Two timer relays with similar dials or terminal counts can still perform different sequences.

Required control result	Likely timer function	Critical point to verify
Wait before turning the output ON	On-delay	What starts timing and what resets it
Keep the output ON after a command ends	Off-delay	Whether control power remains available during timing
Turn the output ON for one defined period	Interval or one-shot	Power-triggered versus signal-triggered operation
Alternate ON and OFF repeatedly	Repeat-cycle	ON-first/OFF-first behavior and whether the two times are independent
Transfer a motor starter from star to delta	Star-delta	Dedicated changeover sequence and interlocking requirements
Use one device for several possible sequences	Multifunction	Available modes, selector settings, and commissioning control

This page is the orientation hub for timer relay functions and applications. For a narrower terminology explanation, start with What Is a Time Relay?.

How a Time Delay Relay Works

At orientation level, every timer relay can be understood as four blocks:

Supply or trigger condition
            ↓
      Timing function
            ↓
   Output changes state
            ↓
 Reset condition restores or restarts the sequence

The input may be the application of control power, a separate trigger signal, or the removal of a signal. The timing circuit evaluates that event against the selected function and preset time. The output then changes a relay contact or, on some designs, an electronic output. The reset condition determines what happens when the signal changes again or power is interrupted.

That last point is easy to miss. “Five-second timer” does not describe a complete device. A useful functional specification must say what happens before, during, and after those five seconds, and what cancels or restarts the sequence.

The operating-mode descriptions below are practical categories, not a universal naming code. Manufacturers can use different mode letters and names, so the timing diagram in the exact datasheet remains authoritative.

Six Practical Types of Time Delay Relays

The diagrams compare timing behavior conceptually. Terminal markings and product details shown in the graphic are not universal wiring instructions.

The six categories below cover the most common selection conversations. They are not mutually exclusive product constructions: a multifunction relay may contain several of the operating functions listed beside it.

Practical category	Timing begins when	Output during timing	Output after timing	Main selection risk
On-delay	Supply or qualifying trigger turns ON	Remains in its initial state	Changes state	Input may not remain valid long enough to complete timing
Off-delay	Qualifying trigger turns OFF	Remains in its operated state	Returns to its initial state	Confusing signal off-delay with operation after total power loss
Interval	Supply or trigger initiates the cycle	Operates for the preset interval	Returns to its initial state	Choosing the wrong trigger or retrigger behavior
Repeat-cycle	Supply or trigger initiates cycling	Alternates ON and OFF	Continues until its stop/reset condition	Assuming every model starts in the same state
Star-delta	Motor-start command initiates the sequence	Star stage is maintained	Star releases and delta is permitted	Using a general timer without the required transition logic
Multifunction	Depends on the selected mode	Depends on the selected mode	Depends on the selected mode	Incorrect mode, time range, or setting during commissioning

On-Delay Timer Relay

An on-delay relay delays output operation after its initiating condition becomes true. A common power-triggered sequence is:

Input ON → timing starts → preset time expires → output operates
Input OFF → output returns and timer resets

Use on-delay when equipment must wait before starting—for example, to stagger contactor commands, prevent an immediate compressor restart, or establish a startup order. If the initiating signal disappears before time expires, many on-delay modes reset without operating the output; signal-memory and pulse-triggered exceptions must be checked in the datasheet.

Off-Delay Timer Relay

An off-delay function is used when the output should remain operated after a command signal ends. In a common signal-triggered design:

Trigger ON → output operates
Trigger OFF → timing starts → preset time expires → output returns

Typical uses include fan post-run, purge time, delayed lighting turn-off, and holding an auxiliary control signal during shutdown. A standard off-delay mode often needs its timer supply to remain available while the trigger input changes. This is different from maintaining an output after the timer itself loses power.

For a focused timing comparison, see On-Delay vs Off-Delay Timer.

Interval and One-Shot Timer Relay

An interval function operates the output for a defined period and then returns it automatically:

Trigger → output operates and timing starts → preset time expires → output returns

This behavior fits a dosing pulse, alarm pulse, signal extension, or other fixed-duration action. “Interval” and “one-shot” are sometimes used for closely related modes, but they are not guaranteed to have the same trigger, reset, or retrigger behavior. Check whether the cycle begins at power-up or from a separate signal, whether a new trigger restarts timing, and whether the input must be removed before another cycle can begin.

Repeat-Cycle Timer Relay

A repeat-cycle timer alternates its output between ON and OFF states:

ON for T1 → OFF for T2 → repeat until stop or reset

It is commonly used for flashing signals, periodic ventilation, lubrication cycles, and simple intermittent operation. Before selecting one, verify whether the first period is ON or OFF, whether T1 and T2 are independently adjustable, and what the relay does after a supply interruption.

Star-Delta Timer Relay

A star-delta timer is a specialized motor-control timer. It coordinates the transition from the star starting stage to the delta running stage in a starter designed for that method.

Stage	Required control result	Timer responsibility
Start	Main and star paths are commanded according to the starter design	Begin the star period
Transition	Star must release before delta is enabled	Provide the defined changeover sequence
Run	Delta path remains enabled with the main path	Hold the final control state
Stop or trip	Starter contactors release	Reset for the next start

The correct star period and transition behavior depend on the motor, contactors, mechanical load, and complete starter design. A general on-delay timer is not automatically an acceptable substitute for a dedicated star-delta function, and this overview is not a starter wiring instruction.

Multifunction Timer Relay

A multifunction timer relay combines several selectable modes in one device. It can be useful for flexible OEM panels, distributor stock, maintenance spares, and projects whose timing logic may change.

Flexibility also creates a commissioning risk. A compatible supply and terminal layout do not compensate for a wrong mode selection. Record the function, time range, dial or digital setting, trigger behavior, and reset behavior in the panel documentation. For fixed, high-volume equipment, a single-function model may reduce setting errors; see Multifunction vs Single-Function Timer Relays for the full decision.

Off-Delay vs True Power-Off Delay

This distinction deserves a separate checkpoint because the two requirements sound similar but have different energy conditions.

Requirement	Timer supply while delay runs	What must be verified
Signal off-delay	Usually remains available	Trigger input, output state, and reset sequence
True power-off delay	Main supply is removed	Whether the exact device can maintain its output, for how long, and under what load conditions

In a conventional electronic off-delay arrangement, the timing electronics and output mechanism still need energy while counting down. If the timer loses all supply and has no specified stored-energy or latching arrangement, it cannot be assumed to continue timing.

Therefore, do not select a “power-off delay” application by the words off delay alone. Use the exact timing diagram and product documentation, especially for purge, brake, alarm-hold, or controlled-shutdown circuits.

Other Ways Timer Relays Are Classified

Function describes the required signal sequence. Procurement also requires a separate classification of how the device is adjusted, mounted, and connected to the control system.

Classification layer	Common options	Why it matters
Function coverage	Single-function, multifunction	Controls flexibility and setting-error risk
Timing implementation and interface	Electromechanical or pneumatic legacy designs; analog electronic; digital electronic	Affects adjustment method, replacement fit, available modes, and documentation
Mounting	DIN rail, plug-in socket, panel mount, printed circuit board	Affects panel space, wiring, replacement, and operator access
Output interface	Relay contact, transistor output on supported models	Determines how the timer interfaces with a contactor coil, programmable logic controller input, or other control load
Trigger arrangement	Supply-triggered, separate signal-triggered, model-specific inputs	Determines what starts and resets timing

Do not infer accuracy, time range, contact capacity, environmental limits, or certification from the technology or mounting label. Those are exact-model specifications. The time delay relay datasheet guide explains how to verify them.

Time Delay Relay Applications by Control Requirement

Use the graphic to compare functional sequences, not to identify universal terminals. Always follow the exact relay timing and wiring diagram.

Application names alone do not select a relay. The useful question is: what must the output do when the control condition changes?

Application requirement	Likely function	Next verification
Start several motors or conveyors in sequence	On-delay	Required sequence, reset behavior, and contactor-coil duty
Prevent immediate compressor restart	On-delay or a dedicated anti-short-cycle control	What event starts the lockout and whether every restart path is covered
Keep a fan operating after a stop command	Off-delay	Whether timer control power remains available
Operate a pump or valve for one fixed period	Interval	Trigger source and retrigger behavior
Flash a beacon or cycle ventilation	Repeat-cycle	ON-first/OFF-first and separate T1/T2 adjustment
Transfer a suitable motor starter from star to delta	Star-delta	Complete starter sequence and interlocks
Standardize a flexible OEM control platform	Multifunction	Mode governance, documentation, and replacement controls

For application-specific design, use the corresponding deep guide rather than treating this table as a final specification. Examples include HVAC compressor timing and pump short-cycle prevention.

How to Select the Right Timer Function

Use these five questions as a first pass:

What exact output timeline is required? Draw the input and output states before choosing a product name.
What starts and resets timing? Distinguish application/removal of supply from a separate trigger signal.
What happens during a power interruption? Specify immediate reset, retained state, restart, or verified power-off-delay behavior.
What will the output switch? Identify the control load and its duty; a resistive current headline is not enough for an inductive contactor coil or solenoid.
What physical and documentation constraints apply? Verify supply, range, mounting, terminals, environment, approvals, and the exact timing diagram.

These questions identify a likely device family, not a purchase-ready part number. Use the timer relay selection guide to convert the application into a complete specification. For model comparison, review the published VIOX timer relay range.

Basic Wiring Boundary

A timer relay normally belongs in the control circuit:

Control supply or trigger
            ↓
        Timer relay
            ↓
   Timed output interface
            ↓
Contactor coil, PLC input, alarm, or other compatible control load

The timer provides timing logic; it is not automatically the device that switches motor power. Terminal designations vary between manufacturers and models, and even familiar markings can serve different functions in different operating modes.

For terminal-level diagrams, use the Time Delay Relay Wiring Guide. For a motor starter, use the dedicated time relay motor-starter wiring guide. Work on de-energized equipment unless an authorized test procedure specifically requires energized measurements, and follow the applicable site and electrical-safety rules.

Setting and Commissioning Checkpoint

Before energizing the controlled equipment:

Match the selected function to the intended input/output timing sketch.
Confirm the time range before setting the fine adjustment.
Verify supply and trigger terminals from the exact model diagram.
Confirm the intended normally open or normally closed output path.
Check output duty for the connected control load and use appropriate suppression where required by the component documentation.
Test the sequence under controlled conditions, including reset and power-interruption behavior.
Record the mode, range, final setting, and model reference in the panel documentation.

If a bench test is required, follow the step-by-step time delay relay test guide rather than improvising inside an energized panel.

Quick Troubleshooting Triage

Symptom	First checks	Deeper resource
No indication or timing activity	Correct supply, protective device, terminal identification	Time delay relay not working
Timing starts but the output never changes	Function selection, qualifying trigger, output terminal, reset condition	How to test a time delay relay
Delay or reset is inconsistent	Supply stability, selected range, trigger duration, reset time	Time delay relay not working
Relay operates but the load does not	Load circuit, contact path, coil voltage, contact duty	Relay clicks but load does not operate
Contacts overheat, weld, or fail early	Inductive duty, switching frequency, suppression, interface choice	Why timer contacts fail on inductive loads

The timing diagram is usually more useful than the product name when diagnosing a sequence problem. It shows the required relationship between input, time, output, and reset.

Standards and Rating Boundary

IEC 61812-1:2023 covers requirements and tests for time relays and coupling relays within its stated industrial and residential-use scope. A standard’s scope does not prove that every timer relay is certified, that a complete control panel complies, or that a component is suitable for a particular installation.

For that distinction, see the IEC 61812-1 time relay compliance guide. Always request model-specific declarations, ratings, diagrams, and certificates when they are required for a project or market.

Frequently Asked Questions

What are the main types of time delay relays?

The most common practical categories are on-delay, off-delay, interval or one-shot, repeat-cycle, star-delta, and multifunction timer relays. Power-off delay is another important behavior that must be distinguished from ordinary signal off-delay operation.

What is the difference between on-delay and off-delay?

On-delay waits before operating the output after the initiating condition appears. Off-delay operates the output first and waits before returning it after the qualifying trigger is removed. The exact supply, trigger, and reset arrangement is model-specific.

Can an off-delay timer keep working after all power is removed?

Not automatically. Many off-delay modes require timer power to remain available while a separate trigger changes state. If the output must remain active after total supply loss, select a device with explicitly documented power-off-delay behavior.

Is a multifunction timer always better than a single-function timer?

No. Multifunction timers reduce part-number variety and offer flexibility. Single-function timers can simplify commissioning and reduce accidental mode changes in fixed equipment. The better choice depends on the application and configuration-control process.

Can a timer relay switch a motor directly?

A timer relay is normally used in the control circuit to command a correctly rated contactor or motor starter. Whether any output can switch a particular load depends on the exact output rating, utilization duty, load characteristics, and manufacturer instructions.

Are terminal numbers the same on every time delay relay?

No. Some numbering conventions are common, but terminal functions, trigger inputs, second contact sets, and timing modes vary. Use the wiring and timing diagram for the exact manufacturer and model.

Sources

Evaluate a VIOX Timer Relay for Your Control Sequence

Once the required timing function is defined, compare the published VIOX timer relay series by operating mode, supply, time range, trigger arrangement, output duty, and mounting. For OEM or panel-building support, send the timing sketch and application requirements to [email protected].