Time Delay Relay : Circuit, Working & Its Applications

A Relay is a constructive element used to control high power with extremely less power consumption. These are also used for processing signals & they can also be utilized like switches. Generally, a normal relay is an electrical device that functions like an electrically operated switch. Once the flow of current reaches the coil of the relay then the open contacts will get closed, & the closed contacts will get open. Once there is no flow of current in the relay coil, then contacts will come back to their original position. There are different types of relays available in the market which are used based on the requirement. So this article discusses one of the types of a relay namely – time delay relay – working with applications.

What is a Time Delay Relay?

A relay that has a timing element device that intentionally delays the switching ON/OFF of the armature immediately once the power supply is applied or removed from the relay is known as a time delay relay. A time delay has an inbuilt time delay function, so the relay will not activate immediately once it is activated although it will wait for a fixed amount of time.

So this kind of relay is applicable where delays are required before the relay activates like security systems & industrial automation. Some kinds of relays have a type of shock absorber system which is connected to the armature that avoids complete movement once the coil is either activated or deactivated. The time delay relay symbol is shown below.

Time Delay Relay Symbol
Time Delay Relay Symbol

Time Delay Relay Working Principle

The Time delay relay working principle is to provide a change of the contacts state that is simply controlled by activating or deactivating the timer. Whenever the timer is activated or deactivated, the timer will start counting from ‘0’ to the current time, called accumulated time. When both the pre-set time & accumulated time are equivalent then the timer contacts will modify the state.

Time Delay Relay Circuit Diagram

The time delay relay circuit using a 555 timer IC is shown below. The main function of this relay circuit is to activate the relay from seconds to minutes once the S1 switch is pushed. This circuit is very simple to design and uses basic electronic components. The required components to build this circuit mainly include; 9V to12V DC Supply, Switch, 555 Timer IC, Resistors like 1M & 470 ohms, 100uF ceramic capacitor, 12V relay, 1N4007 1 diode, 5mm LED, and breadboard. Connect the circuit as per the circuit diagram shown below.

Time Delay Relay Circuit with 555 IC
Time Delay Relay Circuit with 555 IC

A time delay relay is one type of switch that operates between two terminals electrically like NC (normally closed) and NO (normally open) which mainly depends on activating & deactivating the coil within the relay. There are some relays where the switching procedure is not instantaneous & takes some time, so they provide a time delay between activating & deactivating the coil. So, these types of relays are known as time delay relays.


The main dissimilarity between a normal relay and a time delay relay is; normal relay switches immediately from an NC terminal to a NO terminal whereas in a time delay relay, the contacts are ed or closed only after a fixed time interval.


The above time delay relay wiring diagram operates with 9V to 12V DC. In this circuit, a 1000uF electrolytic capacitor is used for setting the time delay to 2 minutes approximately. So, this time delay mainly depends on the capacitor value which means, the time delay is increased once the capacitor value is increased.

At the input pin of the 555 IC with a capacitor, a switch is utilized. Once we turn ON the switch, the relay will be turned ON & it provides the time delay. So the condition of this relay whether it is turned ON or OFF will be indicated with an LED using a 470 ohms resistor. This circuit is helpful in protecting sensitive electronic devices from surges & spikes, controlling flashing lights, and delaying control in the soft start of the motor.

Time Delay Relay Types

There are different types of time delay relays available in different operation methods and sizes. Generally, the relays will change in the mode of operation. There are also other types of time relays available which are multi-functional. So depending on the application requirements as well as other factors like accuracy, price & switching action, you can select a time delay relay.

On Delay Timer Relay

This is the most frequently used type of delay time relay. Once the input voltage is applied then this relay will begin the timing action & after the set timing, it will energize the output. When the input voltage is removed then it will de-energize the output after the relay will reset. These relays are mainly used in applications wherever it is required to ensure that a certain procedure has taken place before beginning another procedure. The applications of these relays mainly include the following.

On Delay Timer Relay
On Delay Timer Relay
  • It is used in blower motors to delay the startup of the blower.
  • Used in burglar alarms to delay the alarm sounding by allowing the time of authorized persons to leave the premise.
  • It operates door locks that should wait a few seconds once the power is given to check whether the door is closed or not before locking it.
  • It is used in fan controls.

Off-Delay Timer Relay

This kind of timer relay needs a trigger to begin timing once it gets an input voltage. The output of this relay will be energized on the application of the trigger and this trigger must be detached for the time delay to start. At the time the delay period ends, an output is de-energized. Once the trigger is provided throughout the delay, then it will reset.

Off Delay Timer Relay
Off Delay Timer Relay

These timers are used within AC systems to hold the blower motor for a particular time period once the thermostat turns off the cooling compressor. These are also used for operating motors & electrical devices for a fixed period of time like coin-operated dryers within commercial laundries. Other applications mainly include telephone circuit control, elevator door control & gas valve controls.

One Shot Timer Relay

One-shot timer relays are also known as interval-on-operate time relays, single pulse timers, single-shot interval timers, and single-shot timers. As the name suggests, this relay triggers simply once.

One Shot Timer Relay
One Shot Timer Relay

The main function of this relay is to trigger a circuit once a fixed amount of time has passed. These relays are activated through power. Once power is applied, the contacts of the relay will move to a different location and stay in this position for the time set previously and after that come back to their unique spot. These timers are frequently used in industrial settings like operating machinery with a start or stop buttons and also used in welding machines to make time adjustments for spot welding.

Interval Timers

Interval timers are mainly used for controlling the duration of time taken for energizing an electrical load. These types of time delay relays are also known as, bypass timing, interval delay, pulse shaping &delay on energization through immediate transfer timers. These relays simply work by delaying the application of power to a load until a specific time has passed.

Interval Timer
Interval Timer

Once the timer has passed, then power is applied & stays on until the timer terminates. At this position, power is detached from the electrical load & turns off until power is applied again.

Recycle Timers

This type of time delay relay is mainly used to switch on & off the cycling of a load. These are also known as repeat cycle timers. These are very helpful in conserving energy by turning ON & OFF a load at regular intervals and also they create a flashing effect. These are either multi-function or single-function devices. These kinds of time delay relays are frequently used in applications wherever it is necessary to cycle power to an electrical system or a device.

Recycle Type
Recycle Type

The common application o time delay relay is in HVAC systems to turn on & off the compressor again at normal intervals. So this helps by preventing the system from overheating. It is also used in electrical equipment to turn ON & OFF the device at specific intervals.

Flasher Timer Relay

The contacts in this type of timer relay energize and de-energize continuously at regular intervals. Usually, this will happen after an input voltage is applied. These time delay relays are regularly used in different applications where it is required to specify that a process or system is working. These are also used in emergency lighting systems wherever the light should flash at normal intervals to specify that the system is working.

Flasher Type
Flasher Type

How to Test Time Delay Relay?

Time delay relay can be tested by using the burden test. The step-by-step of this test is given below.

  • First change the timer by high time delay for instance: 2 minutes.
  • Activate the relay with 125V & measure the DC current.
  • Before the timer works, note down the current value.
  • After two min relay will pick up, and make a note of the current value after the operation.
  • Measure the power of a relay (W) = 125v x measured current.


The advantages of time delay relay include the following.

  • These relays are helpful in control logic implementation with ECS (electronic control systems), DCS, or PLCs.
  • It schedules in starting or stopping of machinery.
  • This relay sets delay time from seconds to hours.
  • By using these relays, energy can be conserved.
  • Electrical separation is possible between small & large currents.
  • By using this relay, managing different variables like voltage and power is possible.
  • This relay can be controlled from remote stations.


The disadvantages of time delay relay include the following.

  • They have a complex structure.
  • The size is large.
  • They have a short life.
  • These are expensive.
  • Its accuracy is simply affected by the power frequency.


The applications of time delay relay include the following.

  • The time delay relays mainly involve in different commercial and industrial applications like buildings, machines, HVAC, water segments, etc.
  • Time delay relays are frequently utilized in machine control-based applications for providing switching to cyclic machinery. So this can assist to avoid the equipment from damaging or sticking.
  • These relays are useful in delaying multiple lamp row switching in greenhouses or production services. So this helps in conserving energy by simply avoiding lamps from being switched on once they are not required.
  • These are used for irrigation systems & Pump controls.
  • These are used in HVAC systems for controlling centralized water systems & fans. So this helps in conserving energy & maintaining buildings very comfortable.
  • These relays trigger alarms once a fixed amount of time has elapsed. So this is very useful for monitoring & security purposes.

Thus, this is an overview of time delay relay – working with applications. These are simply controlled relays with an inbuilt time delay. The flasher timer relay function is to control an event depending on time. Here is a question for you, what is the function of a relay?