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Open secondary on a current transformer

Aviation Mechanic General (AMG) practice question 24 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K17 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA current transformer in an AC generator system is not being used but remains installed. What must be done with its secondary output connections while the system is operated?

  1. ALeave them open so the transformer cannot overheat
  2. BDisconnect the primary power lead from the generator instead
  3. CConnect them together with a jumper
Show the answer and explanation

Correct answer: C. Connect them together with a jumper

  • A — incorrect Leaving the secondary open is the dangerous condition; it can produce dangerously high voltages and overheat the transformer.
  • B — incorrect The primary is the current-carrying power lead itself; the precaution concerns the secondary, which is jumpered rather than removing the primary lead.
  • C — correct The secondary of a current transformer must never be left open while the system is operating, so the output connections are jumpered when the transformer is not in use.

BACKGROUND

Current transformers are used in AC power supply systems to sense generator line current and provide a proportional current for protection and control devices. A current transformer is a ring-type transformer that uses a current-carrying power lead as its primary. Its sides are marked H1 and H2, and it must be installed with H1 toward the generator for proper polarity. The secondary should never be left open while the system is operated, because doing so can cause dangerously high voltages and overheat the transformer; when the transformer is left in the system but not used, its output connections are connected with a jumper.

STUDY TIP

Treat an open current-transformer secondary as a hazard, not a harmless idle state.

KEY POINTS

  • A current transformer uses the power lead as its primary.
  • Install with the H1 side toward the generator.
  • Never leave the secondary open; jumper it when unused.

SOURCES

  • FAA-H-8083-30B ch12 "Current Transformers"
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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.