If a current transformer is unused but connected to a live circuit, which action is recommended?

If a current transformer is unused but connected to a live circuit, which action is recommended?

• A. Arc-flash hazard
• B. Unused current transformer
• C. Minimum depth of working space
• D. Enclosure-type number mark

Answer: (B)

When a current transformer is installed on a live circuit but not being used, the safest approach is to treat it as an unused device and isolate or tag it accordingly. This prevents any confusion or accidental energizing of the CT or its secondary, which can lead to mis-wiring, unexpected currents, or arc-flash risks. Labeling and isolating an unused CT communicates clearly that this portion of the circuitry is not in service, so technicians won’t rely on it as part of normal operation. The other options don’t address the situation directly. Arc-flash hazard is a potential risk in this scenario, but saying it’s an arc-flash hazard doesn’t describe the appropriate action. The minimum depth of working space and enclosure-type number mark relate to general safety or enclosure requirements rather than how to handle an unused CT on a live circuit.

When a current transformer is installed on a live circuit but not being used, the safest approach is to treat it as an unused device and isolate or tag it accordingly. This prevents any confusion or accidental energizing of the CT or its secondary, which can lead to mis-wiring, unexpected currents, or arc-flash risks. Labeling and isolating an unused CT communicates clearly that this portion of the circuitry is not in service, so technicians won’t rely on it as part of normal operation.

The other options don’t address the situation directly. Arc-flash hazard is a potential risk in this scenario, but saying it’s an arc-flash hazard doesn’t describe the appropriate action. The minimum depth of working space and enclosure-type number mark relate to general safety or enclosure requirements rather than how to handle an unused CT on a live circuit.