Definition
An electromagnetic switch designed to remain energized for long, uninterrupted periods without overheating or burning out. It uses a coil of wire to produce a magnetic field that holds a set of heavy-duty contacts closed, allowing high current to flow through a circuit for as long as the coil is powered.
Plain English
A heavy-duty electrical switch that an electric signal turns on, and that can safely stay turned on all day without getting too hot or wearing out.
Context Anchor
Seen in aircraft electrical system maintenance, especially around battery, master switch, and power distribution circuits.
Derivation
Solenoid comes from the Greek 'solen' meaning 'pipe' or 'channel,' referring to the tube-shaped coil of wire inside it. 'Continuous-duty' simply means it is built to operate continuously, as opposed to an 'intermittent-duty' solenoid which is designed only for short bursts of operation, such as engine starting.
Why Pilots Care
Using the wrong solenoid type on a circuit that stays energized for long periods can cause overheating, failure, or even electrical fires.
Analogy
It is like the difference between a doorbell button and a room light switch. A doorbell is meant to be pressed briefly; a room light is meant to stay on. A continuous-duty solenoid is built for the “stay on” job.
Intuition Check
Continuous-duty does not mean the solenoid is always on. It means the solenoid is built so it can remain on for an extended time when the aircraft system requires it.
Example Sentence 1
The master switch in many light aircraft activates a continuous-duty solenoid that connects the battery to the main electrical bus.
Example Sentence 2
Technicians replaced the intermittent solenoid with a continuous-duty model to support the always-on avionics bus during extended ground time.