Timer relay
A relay that switches its contacts after a set delay, enabling sequenced and timed control.
What it is
A timer relay introduces a time delay into a control circuit. It switches its output contacts a set period after being triggered, rather than instantly.
How it works
Different functions suit different jobs. An on-delay waits the set time after it's energised, then switches. An off-delay switches immediately but waits the set time before dropping out. Other modes include single-shot pulses and cyclic on/off.
Many timers need both a supply and a separate trigger input, and have a set time plus a range multiplier — getting either wrong is a common cause of a timer that seems 'stuck'.
Where it's used
Star-delta changeover, sequenced starts, run-on fans, delayed shutdowns, and lighting time clocks. Choosing the right function (and wiring the trigger) is most of the battle.
Related faults
Timer relay not switching its output
A timer relay is powered but its output contact never changes state — the delayed action (start, changeover, stop) never happens, or it switches at the wrong time.
Timer behaving as the wrong type (on-delay vs off-delay)
The timer switches at the wrong point in the sequence because it's acting as the wrong function — on-delay where off-delay is needed, single-shot where cyclic is needed, and so on.
Star-delta starter not transitioning to delta
A star-delta (wye-delta) starter starts the motor in star but never switches to delta — the motor runs weak/slow, or trips, because it stays in the starting connection.
Related definitions
Relay
A small electrically-operated switch — like a miniature contactor — used to switch or route control signals.
Star-delta starting
Starts a motor in star (lower current) then switches to delta (full power) once it's up to speed.
Control vs power circuits
Low-power control logic decides what happens; the power circuit carries the load — kept separate for safety and clarity.