Safety hazards associated with current transformers (CTs)?

• A. CTs can overheat when left idle.
• B. CTs can produce extremely high voltages when the CT's circuit is opened with current flowing.
• C. They emit loud noises.
• D. They require periodic oil changes.

Answer: (B)

When a current transformer is carrying current, its secondary winding must always be closed through a burden or shorted to provide a path for the secondary current. If that secondary circuit is opened while primary current is flowing, the transformer will generate a very high voltage on the secondary in an attempt to maintain ampere-turn balance. The energy stored in the magnetic field has nowhere to go, so a voltage spike can arc over insulation, shock anyone nearby, and damage meters, relays, or other connected equipment. This is the main safety hazard with CTs. The other statements aren’t typical dangers: CTs don’t normally overheat just from being idle, they don’t emit loud noises as a primary hazard, and they don’t require oil changes.