What Is a Time Relay (Timer Relay)?

A time relay (also known as a timer relay) is an electronic component used in electrical circuits or machine control systems to control power contactors based on time parameters. Time relays automatically manage the start of circuit/machine operation and stop the system when the preset time expires. Time relays are circuit elements designed with multiple timing modes, features, and functional variations. You can find detailed information about time relay types, specifications, working principles, and wiring logic in the rest of this article.

What Are the Types of Time Relays?

Time relay models stand out with designs engineered for different automation functions. Their main operating modes include:

On-Delay Timer Relay (Pull-In Delay)

These models begin counting time immediately when voltage is applied to the coil. When the preset time ends, the relay automatically disconnects from the circuit. This type is also referred to as a standard (forward) time relay.

Off-Delay Timer Relay (Drop-Out / Reverse Delay)

These models change the contact position only after coil power is removed and the preset time expires. They are also known as reverse time relays.

Release-Delay Timer Relay (Latching + Return Delay)

The relay pulls in instantly when energized, stays in the active position during timing, and returns to its original (initial) state when the preset time ends.

Star-Delta Timer Relay

These relays are commonly used for high-power industrial motors. When energized, they provide a star connection at first, then switch to delta mode after the preset delay, supporting a safer motor start topology.

Flasher Timer Relay (Oscillating ON/OFF Timer)

These models start oscillation when voltage is applied to the coil, maintain position for the preset time, and return to the initial state when time ends. As long as the coil remains energized, the ON/OFF cycle continues automatically.

Asymmetric Flasher Timer Relay

These models include two independent timing parameters. Coil energization causes the contacts to toggle positions at different timing intervals.

What Does a Time Relay Do?

Time relays play a critical role in industrial and building automation by managing time-based switching tasks. They prevent current from exceeding the specified ampere rating, operate in series with the load, and provide system protection during overload, short circuit, or unstable voltage conditions. Example use case: a time relay can activate or deactivate a heating system at specific temperature or time cycles. While improving operational reliability and circuit safety, time relays also deliver a major advantage in energy efficiency and controlled automation.

How Does a Time Relay Work?

Time relays operate with a simple timing + scanning loop logic:

In on-delay models, the timer begins when the coil is energized.

When the preset time ends, the relay changes contact state:

A normally open (NO) contact closes,

A normally closed (NC) contact opens.

In off-delay models, the contact state changes instantly when energized, but does not return until coil power is cut and the preset time finishes. The cycle time depends on the internal clock speed, program length, and coil/contact architecture. Typical scan cycle duration in industrial timer relays is approximately 3–10 ms, depending on command complexity and timing circuitry.

Where Are Time Relays Used?

Time relays are used in a wide range of engineering applications, such as:

Agricultural and garden irrigation systems: timed pump control

Industrial process automation: conveyor lines, production sequencing

Public outdoor/indoor lighting systems: parks, streets, hospitals, schools, mosques

School signaling systems: bell timing intervals

HVAC automation: periodic heating/cooling control

Automotive systems: motor control coordination in embedded automation

What to Consider When Selecting a Time Relay?

Key engineering criteria include:

Correct timing mode support (on-delay, off-delay, flasher, star-delta, asymmetric, etc.)

Supply voltage compatibility with the control/command circuit feed

Required contact count and topology (NO/NC combinations based on design needs)

Device size compatibility with the mounting environment

Trimpot or display clarity for timing adjustment (display-based models are preferred for easier diagnostics)

LED indicators for timing and contact state visibility

Price-performance balance aligned with the project budget

How to Wire a Time Relay?

When connecting a time relay, the installer should:

Follow the terminal legend and schematic printed on the relay body,

Match coil input, load output, and trigger terminals exactly to the wiring diagram,

Ensure compliance with the manufacturer installation guide for safe and correct wiring.

The wiring diagram indicates which terminals receive coil voltage, which connect to the load, and which handle timing feedback or triggers. For proper and safe installation, the manufacturer’s technical documentation must always be followed.