Selective coordination is achieved when OCPDs are chosen such that, on an overcurrent event, the nearest line-side OCPD opens to interrupt the fault and one or more upstream larger ampere-rated OCPDs open.

Selective coordination is achieved when OCPDs are chosen such that, on an overcurrent event, the nearest line-side OCPD opens to interrupt the fault and one or more upstream larger ampere-rated OCPDs open.

• A. True
• B. False
• C. Only for DC systems
• D. Only when arc energy limits are met

Answer: (B)

Selective coordination means protective devices are set to trip in stages so the device closest to the fault clears it, and upstream devices stay closed unless the fault isn’t cleared downstream. The idea is to isolate only the faulty section and keep the rest of the system powered, which improves reliability and minimizes outages. The statement describes the nearest line-side device opening to interrupt the fault and then upstream larger devices also opening in the same event. That would cause a larger portion of the system to lose power unnecessarily. In proper selective coordination, the downstream device should clear the fault first, and upstream devices should only trip if the fault isn’t cleared downstream or the downstream device fails. So the claim is not correct. Selective coordination applies to both AC and DC systems, and it isn’t determined by arc energy limits.

Selective coordination means protective devices are set to trip in stages so the device closest to the fault clears it, and upstream devices stay closed unless the fault isn’t cleared downstream. The idea is to isolate only the faulty section and keep the rest of the system powered, which improves reliability and minimizes outages.

The statement describes the nearest line-side device opening to interrupt the fault and then upstream larger devices also opening in the same event. That would cause a larger portion of the system to lose power unnecessarily. In proper selective coordination, the downstream device should clear the fault first, and upstream devices should only trip if the fault isn’t cleared downstream or the downstream device fails. So the claim is not correct.

Selective coordination applies to both AC and DC systems, and it isn’t determined by arc energy limits.