Definition
A heavy-duty, electrically controlled switch used to open and close high-current circuits in an aircraft electrical system. A small control current energizes a coil, which magnetically pulls a set of large contacts together to complete the main power circuit. Contactors are commonly used for battery, starter, generator, and external power circuits where currents are too high for ordinary cockpit switches to handle directly.
Plain English
A big remote-controlled switch. A small switch in the cockpit sends a low current to the contactor, and the contactor itself does the heavy work of connecting or disconnecting the high-current power line.
Context Anchor
Seen in aircraft electrical system maintenance, especially around batteries, starters, generators, and power distribution panels.
Derivation
From the Latin contactus, meaning 'a touching.' The name reflects what the device physically does: it makes or breaks contact between two heavy electrical terminals.
Why Pilots Care
When a pilot turns the battery master or starter switch, they are not actually carrying the heavy current themselves — they are commanding a contactor to do it. If a contactor fails, the cockpit switch may work but the engine won't crank or the battery won't connect to the bus.
Analogy
Like a doorbell button that rings a much louder bell elsewhere in the house — a small action triggers a much bigger one in another location.
Intuition Check
Do not think of a contactor as just a plug or connector. A connector joins wires or components; a contactor actively opens or closes an electrical circuit.
Example Sentence 1
When the pilot turns on the battery master switch, the battery contactor closes and connects the battery to the main bus.
Example Sentence 2
The mechanic replaced the faulty contactor after it failed to engage the hydraulic pump motor.