Time Delay Relay: On-Delay vs Off-Delay Timers Explained
Time delay relays (timer relays) are among the most common parts in a control panel. They delay switching on or off, sequence motors, and keep fans or pumps running for a set time. This guide explains the main timer modes, where each one is used, and how to choose a timer relay.
On-delay timer (delay on make)
When the control signal is applied, the timer starts counting. The output contacts change over only after the set time. When the signal is removed, the output resets immediately.
Typical uses:
- Star-delta starters: switching from star to delta after the motor accelerates
- Staggered starting of several motors to limit inrush current
- Allowing pressure or a process to stabilise before enabling the next step
- Ignoring short signals from a float switch or pressure switch
Off-delay timer (delay on break)
The output switches on as soon as the control signal is applied. When the signal is removed, the output stays on for the set time and then switches off.
Typical uses:
- Running a cooling fan on after a machine or heater stops
- Purging a burner or extracting fumes after shutdown
- Keeping a lubrication or coolant pump running briefly after a spindle stops
- Stair or corridor lighting
Other common modes
| Mode | Behaviour | Example use |
|---|---|---|
| Interval (single shot) | Output on for the set time when triggered, then off | Dosing, horn or alarm pulse |
| Cyclic / flasher | Output alternates on and off | Warning lamps, intermittent lubrication |
| Star-delta timer | Two outputs with a short pause between star and delta | Star-delta starters |
| Multifunction | Several modes selectable on one unit | Stocking one timer for many jobs |
How to choose a timer relay
- Function: on-delay, off-delay, interval, cyclic or multifunction.
- Time range: make sure your setting sits comfortably inside the range, not at its very edge.
- Supply voltage: match the control voltage (for example 230 V AC or 24 V DC).
- Contacts: number of change-over (C/O) contacts and their current rating.
- Mounting: plug-in (with socket) for quick replacement, or DIN rail.
- Indication: LEDs for supply and output status help commissioning and fault finding.
ComatReleco Time Cube timers
Concord supplies Swiss ComatReleco timer relays. The Time Cube CT3 is a plug-in off-delay timer with a time range of 0.1–60 minutes, two change-over outputs, a dial setting with LED status, and a 230 V AC supply. It plugs into an 11-pin socket such as the S3-B, so replacing it takes seconds and needs no rewiring. See the full time relays range for other functions and voltages.
Wiring and commissioning tips
- Check whether the timer needs continuous supply plus a separate control input (common on off-delay timers) or is started simply by applying supply.
- Use the timer’s contacts to switch contactor coils, not motor loads directly.
- Set the time with some margin, then fine-tune during commissioning while watching the process.
Frequently Asked Questions
What is the difference between an on-delay and an off-delay timer?
An on-delay timer switches its output on after the set time once the signal is applied. An off-delay timer switches on immediately and switches off after the set time once the signal is removed.
Which timer is used in a star-delta starter?
An on-delay timer or a dedicated star-delta timer, which switches the motor from star to delta after it has accelerated.
What is a multifunction timer relay?
A single timer with several selectable modes (on-delay, off-delay, interval, cyclic and others), so one part number covers many applications.
Talk to Concord
Concord Automation & Controls has supplied motor protection relays and industrial relays to Indian industry since 1996 and is the exclusive ComatReleco (Switzerland) distributor for India, Bangladesh and Mauritius. Share your motor, pump or panel details and we will recommend the right model: call or WhatsApp +91 96670 40511, email contact@concordrelay.com, or use our contact page.