What Is the Function of Time Delay Relay?

Relays instruct electrical or electronic devices and machines to activate or deactivate when prompted by a user. Generally, we depend on relays to activate numerous appliances, machinery, and equipment, ranging from motor vehicles to conveyor belts. Time delay relays in particular, have a time delay mechanism built in.

Triggered in varying ways, time delay relays are capable of minimizing the amount of energy used to start large industrial machinery or to switch lights or machines ON and OFF at specified times. More than that, they can also be used to ensure that different parts of a machine start separately at predetermined times.

Production and Safety

To control loads or production processes, time delay relays are utilized. For example, a time delay relay ensures that items move from one conveyor to another when necessary. This prevents items from piling up and slowing the production process down.

In terms of safety, a time delay relay offers many advantages. For example, it can provide a scheduled window to clear noxious gasses from furnaces or combustion chambers. This enables a sufficient amount of ventilation for fumes that can cause explosions.

Typically, time delay relays are activated by opening or closing a circuit or by providing an input current. The trigger signal can be designed with a dry-contact control switch like a float switch, limit switch, or push button. It is important to note that there are a multitude of time delay relay types, each of which have timing functions that operate differently.

How a Time Delay Relay Functions

The type of time delay relay you opt for is determined by the system setup. The most basic types are on- and off-delay timers but other types such as interval-on-operate, flasher, and repeat cycle time delay relays are also available.

On-Delay Timers

On-delay timers are normally open and start timing when the input voltage (power) is applied. Meanwhile, the output is energized at the end of the delay. To de-energize the output and reset the time delay relay, the input voltage must be removed. Also called delay-on-operate timers, on-delay timers are used for blower motors to delay operation for a specified time period after a gas, electric, or oil heater has been turned on. On-delay timers are also utilized to stagger starting times for multiple compressors or motors that are activated by the main switch, avoiding excessive surge current in the power line. Other popular applications include power supply sequencing, fan controls, intrusion alarms, and more.

Off-Delay Timers

Off-delay timers, also referred to as delay-on-release, delay-on-break, or delay-on-energization timers, are prepared to accept a trigger when an input voltage is applied. In contrast, an output is energized by applying a trigger but it must be removed for the time delay to start. At the end of the time delay period, the output is de-energized. However, if the trigger is applied during the delay, it will automatically reset.

Usually, off-delay timers are found in air-conditioning systems to keep the blower motor in operation for a specific time period once the thermostat has turned the cooling compressor off. Furthermore, they can also be used to operate electrical devices and motors for specified time intervals, such as coin-operated dryers in laundry mats. Other common applications include gas valve, telephone circuit, and elevator door controls.


Aerospace Simplified is a leading supplier of time delay relay components from top global manufacturers like the United States Postal Service, Leach International Corporation, and many others. With countless top-quality items, we offer rapid lead times and unbeatable cost savings, allowing us to meet our customers’ rigid time constraints and strict budget parameters. For additional questions or concerns, call or email us at any time. If you would like a quick quote on any featured product, submit a Request for Quote (RFQ) form today!


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