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Definition of a relay

Aviation Mechanic General (AMG) practice question 25 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K19 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhat is a relay?

  1. AAn electromechanical switch in which a small current controls a large current
  2. BA switch that opens or closes with a tripping movement of 1/16 inch or less
  3. CA bimetallic switch that opens a motor circuit automatically when the motor becomes excessively hot
Show the answer and explanation

Correct answer: A. An electromechanical switch in which a small current controls a large current

  • A — correct The handbook defines a relay as simply an electromechanical switch where a small amount of current can control a large amount of current.
  • B — incorrect That describes a microswitch, which is named for the very small movement of its tripping device.
  • C — incorrect That describes a thermal protector, or thermal switch, used to keep a motor from overheating.

BACKGROUND

Components in electrical circuits are not all meant to operate continuously, so a switch, a relay, or both are included to control them. A relay is an electromechanical switch in which a small amount of current controls a large amount of current. When voltage is applied to the relay coil, the electromagnet is energized and pulls the common arm down, opening the circuit to the normally closed (NC) contacts and closing the circuit to the normally open (NO) contacts. When the energizing voltage is removed, a spring returns the arm to the NC contacts. The coil's positive connection is designated X1 and its ground side X2.

STUDY TIP

Separate the three control devices by their trigger: relay = coil current, microswitch = tiny mechanical movement, thermal switch = heat.

KEY POINTS

  • A relay lets a small coil current switch a large load current.
  • Energizing the coil moves the arm from the NC contacts to the NO contacts.
  • Coil terminals: X1 positive, X2 ground.

SOURCES

  • FAA-H-8083-30B ch12 "Relays"; "Microswitches"; "Thermal Protectors"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.