What Is an Off-Delay Timer Relay? Types and Selection Criteria
An off-delay timer relay is a timer relay that keeps its output contact energised for a set time after the supply or control signal is removed and then releases it.
An off-delay timer relay is a timer relay that keeps its output contact energised for a set time after the supply or control signal is removed and releases it when the time expires. It is used for jobs such as running a cooling fan on after a motor stops or switching off lighting with a delay.
Types
- Timing on supply loss: There is no separate control input. The relay pulls in while powered; when the supply is removed it keeps the contact energised for the set time using energy stored in its internal circuit. Entes DG-10 and DG-60 are of this type.
- With control input: The relay is powered continuously and a separate control contact starts the timing. When the control contact closes, the output closes; when it opens, timing starts and the output opens at the end of the time. Schneider Electric RE17LCBM is of this type.
- Pneumatic block fitted to a contactor: Schneider Electric TeSys Deca LADR0, LADR2 and LADR4 are not stand-alone relays; they mount on the front of a contactor. When the contactor coil is de-energised, the block's 1NO+1NC delayed contacts change state after the set time. The on-delay LADT blocks of the same range are in the Single-Function Timer Relays category.
Catalog models compared
| Model | Type | Time range | Supply | Output |
|---|---|---|---|---|
| Entes DG-10 | Timing on supply loss | 0.6 s–10 min | 220/230 V AC | 1 C/O, 16 A |
| Entes DG-60 | Timing on supply loss | 1 s–60 min | 220/230 V AC | 1 C/O, 16 A |
| Schneider Electric RE17LCBM | With control input | 0.1 s–100 h | 24–240 V AC | 0.7 A |
| Schneider Electric LADR0 | Pneumatic block on a contactor | 0.3–3 s | Via the contactor | 1NO+1NC |
| Schneider Electric LADR2 | Pneumatic block on a contactor | 1–30 s | Via the contactor | 1NO+1NC |
| Schneider Electric LADR4 | Pneumatic block on a contactor | 10–180 s | Via the contactor | 1NO+1NC |
Entes and RE17LCBM values are taken from the manufacturers' datasheets, LADR values from the product name. For Schneider Electric RE10RCMUN (Harmony, with off-delay function) and Tense ERV-DG, check time and supply values on the product page.
Selection criteria
- What starts the timing: If timing must start when power is lost, choose the supply-loss type; if a separate button, sensor or contactor contact must start it, choose the control-input type.
- Time range: The longest time you need must fall within the model's setting range.
- Supply: The relay supply voltage must match the control circuit. DG-10 and DG-60 run on 220/230 V AC only.
- Output and load: The 0.7 A output of RE17LCBM is for a contactor coil or small loads; loads such as fans, pumps and motors are switched through a contactor.
- Mounting: DG, RE17 and RE10 are rail-mounted relays. LADR blocks fit only on the front of compatible TeSys Deca contactors.
Common mistakes
- Confusing it with an on-delay relay: An on-delay relay pulls in with a delay after power is applied; an off-delay relay releases with a delay after the command ends. One cannot replace the other.
- Testing a DG right after first power-up: According to Entes, the relay must stay powered for up to 90 seconds to reach the ready state.
- Expecting a new setting to apply at once: On DG-10 and DG-60 a new time setting applies only after the voltage is switched off and on again.
- Using a control-input relay by cutting its supply: On relays such as RE17LCBM, timing starts when the control contact opens while the supply stays on; if the relay's own supply is cut, no off-delay is obtained.
- Treating an LADR block as a stand-alone relay: LADR0, LADR2 and LADR4 do not mount on a rail and have no coil of their own; they do not work without a contactor.
Related standard
- IEC 61812-1: Covers time relays for industrial and residential use; function definitions and accuracy values of timer relays are stated to this standard.
Brands in the catalog
The Off-Delay Timer Relays category has 8 active products: Schneider Electric 5 (RE17LCBM, RE10RCMUN, LADR0, LADR2, LADR4), Entes 2 (DG-10, DG-60), Tense 1 (ERV-DG). If you need only one function, see Single-Function Timer Relays; if you also need on-delay, flasher or other functions besides off-delay, see Multi-Function Timer Relays and confirm the function in the datasheet.
Frequently asked questions
What is the difference between an off-delay and an on-delay timer relay?
An on-delay relay waits for the set time after power or a command arrives and then pulls in. An off-delay relay pulls in as soon as the command arrives and, when the command ends, stays energised for the set time before releasing.
How does the relay keep timing after the supply is removed?
Models that time on supply loss store energy in their internal circuit while powered and use it to complete the time. Entes DG-10 and DG-60 must stay powered for up to 90 seconds to reach the ready state.
Which type suits running a fan on after a motor stops?
You can use a supply-loss relay (Entes DG-10, DG-60) connected to a line that is de-energised together with the motor contactor, or a control-input relay (RE17LCBM) that takes the motor contactor's contact into its control input. The fan should be run by the contactor the relay drives, not by the relay itself.