Timer Relays Selection Guide
A timer relay changes its contact once the set time has elapsed after a signal arrives or is cut off. On-delay, off-delay and flasher types.
What is a timer relay? A timer relay is a relay that changes the position of its output contact once a set time has elapsed after the supply or control signal arrives or is cut off. It is used to delay or sustain an operation for a set time in motor starting, lighting, ventilation and pump control. It is selected by its time functions, such as on-delay, off-delay and flasher.
This guide covers the points to look at when choosing products in the Timer Relays category.
Time functions and subgroups
- On-delay: after the supply or start signal arrives, the contact changes position once the set time has elapsed. In the Single-Function Timer Relays group, the time range is given in the model name (up to 30 seconds, up to 12 minutes, and so on).
- Off-delay: after the control signal is cut off, the contact stays energized for the set time; a typical example is a cooling fan that keeps running for a while after the motor has stopped. It has two designs: in one the supply stays connected continuously and the time is started from a separate control input, and in the other the time starts when the supply is cut. The related group: Off-Delay Timer Relays.
- Flasher: the output switches on and off continuously with its on and off times. If the times are equal it is called a symmetrical flasher, and if they are set separately an asymmetrical flasher. The related group: Flasher Timer Relays.
- Star-delta: counts the star time, releases the star contactor and, after a short changeover time, pulls in the delta contactor. The related group: Star-Delta Timer Relays.
- Forward-reverse: operates two outputs in sequence with a pause between them; used in drives that rotate by changing direction. The related group: Forward-Reverse Timer Relays.
- Multi-function: offers several of these functions in a single housing; the function is selected on the device. In the Multi-Function Timer Relays group there are models with 8 and 13 operating modes.
The special relays that manage the wash and rinse times of industrial dishwashers and the precision-setting model are in separate subgroups.
The difference between a timer relay and a time switch
A timer relay counts time after an event (energy arriving, a contact closing); it does not know what time of day it is. A time switch, on the other hand, switches its output on and off at specific times of day according to a daily or weekly program. To run loads such as lighting, signs or pumps by the clock, see the time switches in the Programmable Timer Relays group, and for switching by sunrise and sunset, the Astronomical Timer Relays category.
Selection order
- Function and start method: first decide whether the time will start with the supply or with a separate start (trigger) input. Models with a start or trigger input are indicated in the product name or features.
- Time range: there is a large difference between ranges such as 0,1 s - 60 s and 0,1 s - 100 hours. On models with an adjustment knob (analog), the required time should not be squeezed into the very bottom end of the scale; on models with a digital display, the time is set numerically.
- Supply voltage: there are multi-voltage options such as 220-230 V AC, 24 V AC/DC and 12-240 V AC/DC; match it to the voltage of the control circuit.
- Contact: look at the number and current of changeover (C/O) contacts. For example, in Entes's table MCB-30 and MCB-60 have 1 C/O 8 A, DG-10 and DG-60 have 1 C/O 16 A, and the star-delta relay SER-YU has 2 N/O 5 A contacts. Motors and large loads are not switched with the relay contact but with a contactor driven by the relay.
- Mounting: there are modular-type boxes mounted on a DIN rail, 48 x 48, 72 x 72 and 96 x 96 mm housings mounted on a panel door, and models with an 8-pin or 11-pin socket. For socket models, verify from the product card whether the socket comes with the product.
Timer relay in star-delta starting
A star-delta relay differs from an ordinary on-delay relay in two ways: it has separate outputs for the star and delta contactors, and it leaves a short changeover time between the two. This time is meant to prevent the delta contactor from closing before the star contactor has opened. On the Entes SER-YU, the star time is adjustable between 1-60 s and the changeover time between 20-500 ms. The star time is determined by the motor's run-up time; the interlocking between contactors and the motor protection are installed separately according to the project and the manufacturer's data.
Terminal and contact designations
On DIN rail timer relays, in the common designation the supply is connected to terminals A1-A2, the start (control) input is B1, and the delayed changeover contact is shown as 15-16-18: 15 is the common terminal, 16 the normally closed and 18 the normally open contact. C/O refers to a changeover contact and N/O to a normally open contact. Terminal names vary by manufacturer and housing type, and the numbering is different on socket and panel-mount models; make the connection from the product's own diagram.
Brands in this category
- Tense: single-function, multi-function and flasher relays with the codes ER, ERP, ERV and ERD; in DIN rail and panel-mount housings.
- ABB: timer relays with CT codes (such as CT-MFC, CT-ERD, CT-MVS, CT-APS).
- Schneider Electric: timer relays with RE22 codes and IHP+ digital time switches.
- Entes: MCB series single- and multi-function relays, DG off-delay, SER-YU star-delta, EF-10 flasher and SSR-2X forward-reverse relays.
- Siemens: timer relays with 3RP25 and 7PV15 codes.
- GEMO: single- and multi-function timer relays with DZ and AZ codes; the AZ-coded model has analog adjustment.
Order notes
Timer relays are sold by the piece. Some models are listed as separate products with different supply voltages (for example 24 V and 230 V AC versions); check the voltage suffix of the code before adding to the cart. A small number of products appear as made-to-order; the lead time for these products is confirmed before the order. You can reach a product directly by typing codes such as 3RP2505-1AW30 or MCB-15 into the site search.
Comparison and selection table
| Selection Criterion | On-Delay Timer Relay | Off-Delay Timer Relay | Multi-Function / Flasher / Star-Delta Timer |
|---|---|---|---|
| Timing Logic | Contacts change state after preset time (t) once energized | Contacts remain active and drop out time (t) after trigger/supply stops | Selectable On-Delay, Off-Delay, Cyclic Flasher, Pulse or Star-Delta |
| Time Range | 0.1 s – 30 s / 60 min (single-range) or 0.1 s – 100 hours | 0.1 s – 10 min / 30 min (control-trigger or true power-off delay) | Dip-switch or rotary selector for time base (ms, s, min, h) & mode |
| Supply & Contacts | 24 V AC/DC, 230 V AC or universal 24–240 V AC/DC; 1 CO / 2 CO | 24–240 V AC/DC; 1 CO (SPDT) or 2 CO (DPDT) relay output | 17.5 mm / 22.5 mm DIN-rail module or 8/11-pin plug-in socket |
| Typical Application | Staggered motor starting, conveyor sequencing, alarm delay | Exhaust fan overrun, post-cooling cycles, lighting delay | Periodic lubrication/mixing (cycler), star-delta motor starting |
Frequently asked questions
What is the difference between an on-delay and an off-delay timer relay?
In an on-delay relay the time starts when the supply or start signal arrives, and the contact changes position when the time has elapsed; it is used to bring a load into the circuit with a delay. In an off-delay relay the contact pulls in immediately with the signal, stays pulled in for the set time after the signal is cut off, and then releases; it is for taking a load out of the circuit with a delay. In some off-delay models the supply stays connected continuously and the time is started from a separate trigger input.
Can a normal timer relay be used in star-delta starting?
A relay made for star-delta should be preferred. These relays have separate outputs for the star and delta contactors and leave a short changeover time between leaving star and entering delta; for example, on the Entes SER-YU this time is adjustable between 20-500 ms and the star time between 1-60 s. A single-contact on-delay relay does not provide this changeover time. The circuit is installed together with interlocking and protection according to the project data.
Should I choose a single-function or a multi-function timer relay?
If the function is fixed and will not change, a single-function relay is sufficient; the only setting is the time, and there is no chance of selecting the wrong function. A multi-function relay offers functions such as on-delay, off-delay, pulse and flasher in a single housing, and on some models the time range can also be selected. It suits maintenance teams that want to use the same spare part in different panels and projects where the function will only be settled at commissioning.
Are a timer relay and a time switch the same product?
No. A timer relay counts a period of seconds, minutes or hours after a signal and works independently of the time of day. A time switch works according to the real clock; it switches its output at the on and off times in a daily or weekly program. Keeping a fan running for a while after the motor has stopped is a job for a timer relay, and lighting a sign at a certain hour every evening is a job for a time switch.
Can a motor be connected directly to the contact of a timer relay?
A timer relay is a control element; its contact is sized for a contactor coil, a pilot light or small loads. For example, Entes's table gives an 8 A contact for MCB-30 and MCB-60 and a 16 A contact for DG-10 and DG-60. Loads with a high inrush current such as motors are not switched with the relay contact but through a contactor driven by the relay, and motor protection is provided separately. For the current ratings of the contact by load type, see the manufacturer's data.