Apprentice Lineman General Practice Test 2026 – 400 Free Practice Questions to Pass the Exam

A current transformer (CT) is designed to measure alternating current (AC) by producing a reduced current that is proportional to the current flowing in the circuit being measured. The primary function of a CT is to step down the high currents found in power systems to a lower, more manageable level suitable for measurement and monitoring by meters or protective relays.

The CT works by using an electromagnetic induction principle. The high primary current flowing through a conductor induces a magnetic field, which in turn induces a lower current in the secondary winding of the transformer. This secondary current is a scaled-down version of the primary current, allowing for safe and accurate readings without needing to directly measure high currents, which can be dangerous and impractical.

This ability to reduce amperage makes it easier for devices, such as ammeters and other metering equipment, to interface with electrical systems, ensuring accurate monitoring while maintaining safety standards.