Definition
An electrical relay designed so that its contacts do not open or close immediately when the coil is energized or de-energized, but only after a preset interval of time has elapsed.
Plain English
A switch that waits a set number of seconds before turning a circuit on or off, even after it has been told to operate.
Context Anchor
Seen in aircraft electrical system diagrams, maintenance manuals, and troubleshooting procedures for equipment that must not operate instantly.
Derivation
Built from three plain words: 'time' (the interval), 'delay' (a deliberate pause), and 'relay' (an electrically operated switch). The name itself describes the function: a relay that delays in time.
Why Pilots Care
Several aircraft systems rely on a built-in pause to work safely — for example, allowing an inverter to stabilize before a load is connected, or letting a starter motor disengage before the next step in a start sequence. Recognizing the term helps pilots interpret schematics and troubleshoot systems where a circuit appears to operate slowly by design rather than by fault.
Intuition Check
A time-delay relay is not a relay race or a radio relay. Here, “relay” means an electrical switch, and “time-delay” means the switch waits before acting.
Example Sentence 1
The avionics master uses a time-delay relay so that sensitive equipment is not exposed to the voltage spike that occurs at engine start.
Example Sentence 2
During preflight, the pilot noticed the time-delay relay kept the taxi lights on briefly after switching them off.