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The On Delay Timer Relay Explained

The on-delay timer relay is used in a broad range of applications today, from the lighting systems of buildings to HVACs and industrial machinery. If you’re unfamiliar with the device, continue reading to learn about its function, how it works, and some of its most popular uses.

What is On Delay Timer?

Off delay Timer Relay
On-Delay Timer Relay

A time relay is a type of device, usually either electromechanical or solid-state, that operates a load after a delay. Also called timing relays, time relays work off of two inputs: an activation signal (usually from a switch) and a timing circuit.

The on-delay timer relay is a variation of these types of relays, and the opposite of what’s called an off-delay timer relay.

To help you understand the difference between an on delay timer and off delay timer, we will start by defining the on delay timer. We will also take a look at its function in electrical systems. So, here is the on delay timer meaning and function.

On Delay Timer Definition

An on-delay time relay is a timing device that keeps contacts open or closed until the preset time has elapsed. After that, the contacts will close or open, thereby energizing or de-energizing the output. The time period for delay starts when an input voltage is applied to the device.

Most on-delay timing relay circuits have an internal coil that must be energized before the timing period can start. They can also be solid state timers and only use semiconductors to produce the timing and circuit closing actions during use.

Regardless of if a timing relay is electromechanical or purely electronic, they all have a set of input and output terminals. The input terminal is where the voltage must be applied in order to start the timing function. The output terminals are what supply power to the device or system being controlled by the relay.

On Delay Timer Function

Based on the on-delay timer meaning, we can easily see that it has one main function: to delay the closing of electrical contact. The time delay can range from a few minutes to hours, or even days. It all depends on how the device is set and the available timing options.

Based on this operation method, the on-time delay timer is employed in systems where a process must start only after a specific time has elapsed. This is to ensure that all the conditions are met for safe and correct operation.

One on-delay timer example application is in a door that must remain open for a certain length of time before it automatically closes. Another example is when lights that must stay on for a specific period after someone leaves a room.

On Delay Timer Working Principle

Off Delay Timer Working Principle
The on-delay timer relay working principle

The on-delay timer relay working principle is a pretty simple one. When voltage is applied to the input terminal, current flows through the coil and creates a magnetic field. This, in turn, closes the switch, which then energizes the load. The time delay starts when the coil is energized. When the preset time has elapsed, the switch opens, de-energizing the load.

The details of on delay timer operation depends on if the device is a one function on delay timer or a multifunction on delay timer. One function on delay timers can only be used for one purpose, while multifunction on delay timers have extra timing functions that can be set as needed.

On Delay Timer Application

The on-delay timer application is wide-ranging. You will usually find it used when you need to delay the closing of electrical contacts, or the flow of power to a device or electrical system. Some of the most common uses for on-delay timer relays include:

Blower Time Delay Relay

This is used in HVAC systems to delay the blower from coming on when the thermostat calls for heat. In this application, the on delay time relay helps to prevent the blower from coming on too soon and blowing cold air into the room unnecessarily. The delay ensures the air is heated before circulation.

Motor Start Relay

This is used to delay the start of a motor and often done to allow the motor to build up enough torque to start under load. On delay motor start relay is also used to stagger the starting of multiple motors and prevent overloading the power supply, especially when the motors are connected to one main switch.

Pump Controller Relay

The pump controller relay is used to delay the start of a pump. It prevents the pump from starting when it is not needed to. An example is when the relay is used to stagger the starting of multiple pumps to prevent overloading the power supply.

Industrial Delay Relay

Industrial processes that must be controlled with great precision often use an industrial delay relay. The on-delay feature of the relay allows for the process to be started at a specific time and then accurately repeated. for example, an on-delay timer is often used to start material-carrying belts in a reverse to prevent piling.

Security System Delay Relay

A security system on delay relay is used to delay the activation of an alarm. This can be used to allow people to enter a building before the alarm is activated. It can also be used to delay the alarm so that it goes off after a certain period of time, which can be used to deter burglars.

On Delay Timer Price

The price of an on-delay timer varies depending on the manufacturer, the model, and the features. For example, you can expect to pay anywhere from $10 to $100 for an on-delay timer to control a lighting system in a building or a time relay for other equipment.

An industrial time delay relay will cost more, given their higher ratings and other features such as robust construction. More features also mean a higher price. For example, an on-delay timer with a multifunction operation mode will cost more than a timer that offers fewer modes.

GEYA GRT8-EC timer relay technical parameter:

Function ON delay,Delay off
Supply terminalsA1-A2(AC230V,AC380V),A1-A3(AC/DC24V)
Voltage range                    AC230V(50-60Hz)orAC/DC24V,AC380V(50-60Hz)
Power inputAC max.6VA/1.3W
Supply voltage tolerance                        *  -15%;+10%
Supply indicationgreen LED
Time ranges                                        0.1s-10day
Time settingpotentionmeter
Time deviation ≤10%
Repeat accuracy0.2%-set value stability
Temperature coefficient              0.05%/C,at=20°℃(0.05%°F,at=68°F)
Switching voltage250VAC/24VDC
Min.breaking capacity DC                           500mW
Output indicationred LED
Mechanical life                                    1×10⁷
Electrical life(AC1)1×105
Reset time                                       max.200ms
Operating temperature-20℃ to+55℃ (-4F to 131°F)
Storage temperature                    *  -35℃ to+75℃(-22Fto 158°F)
Mounting/DIN railDin rail EN/IEC 60715
Protection degree                     IP40 for front panel/IP20 terminals
Operating positionany
Overvoltage cathegory                                III.
Pollution degree2
Max.cable size(mm)           solid wire max.1×2.5or 2×1.5/with sleeve max.1×2.5(AWG 12)
Weight                      52g
StandardsEN 61812-1,1EC60947-5-1


The on-delay timer relay is a versatile and flexible device that can be used in a wide variety of applications. It is easy to use and relatively affordable. When choosing a timer for your system, be sure to consider the price, the features, and the application. That’s because different delay timers are better suited for different applications.

Picture of William

I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.


    Learning alot from this great platform

    Hey good article.. I was wondering if this would cycle a pump. Go on when power is initiated then off after 4min for 15min, back on for 4min off for 15min repeat.

    Thanks mark

      We have received your message and our product specialist will contact you as soon as possible. Thank you for contacting GEYA.Have a good day😀

    Bekamen Sie danach noch eine Antwort?

    Wie kommt “Trinken” zustande?

    What is price

    Good article

    So proud of this product of delay timer rela just of it’s significant

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