Which type of transformer is used to step down current to a safe value, a maximum of 5 amps?

• A. Current
• B. Potential
• C. Instrument
• D. Distribution

Answer: (A)

When you want to measure current safely, use a device that takes the large line current and produces a small, proportional current for meters or relays. That is what a current transformer does. It’s designed to step down the high current on the primary circuit to a low, safe secondary current—commonly something like 5 A on the secondary—so protection devices and meters can read or react without handling high energy. The ratio (for example, 1000:5) tells you how much the current is reduced.

This is different from a potential transformer, which lowers voltage for measurement, or a distribution transformer, which reduces voltage to supply customers. So when the goal is to convert current to a safe, manageable value for instrumentation, a current transformer is the appropriate choice. Also, remember the CT secondary must be loaded by a burden (not left open-circuited) to avoid dangerous voltages and improper operation.