Definition
A heavy-duty, electrically operated switch used to control high-current electrical loads in an aircraft. A small control current energizes a coil, which magnetically closes (or opens) a set of large contacts that carry the main load current to equipment such as the starter, battery, or generator.
Plain English
A big, remote-controlled switch. A small electrical signal tells it to close, and once closed it lets a much larger amount of current flow through to power something heavy, like a starter motor.
Context Anchor
Seen in aircraft electrical system discussions, especially around battery, master switch, starter, and power distribution circuits.
Derivation
From the Latin contactus, meaning 'a touching.' The name reflects what the device does: it brings two electrical contacts together to complete a circuit.
Why Pilots Care
Contactors handle the heavy current that ordinary cockpit switches cannot. When you turn the battery master switch or push the starter button, you are not switching the main current yourself, you are commanding a contactor to do it. A failed contactor can prevent the battery from connecting to the bus or stop the starter from engaging.
Analogy
A contactor is like a heavy-duty remote-controlled switch. Your small cockpit switch gives the command, and the contactor handles the bigger electrical power.
Intuition Check
Do not think of a contactor as just any electrical connection. It is a controlled switch that opens or closes a high-power electrical path.
Example Sentence 1
When the pilot pressed the start button, the starter contactor closed and connected the battery to the starter motor.
Example Sentence 2
Power from the battery reached the lights only after the contactor energized and its contacts closed.