Plug-in-type overcurrent protection devices or plug-in-type main lug assemblies that are ___ shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.

Plug-in-type overcurrent protection devices or plug-in-type main lug assemblies that are ___ shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.

• A. 3-phase only
• B. 480-volt
• C. back fed
• D. none of these

Answer: (C)

The key idea is safety in back‑fed installations. When a panel can be back‑fed—power entering the panel from the load side or from a source not connected to the usual line side—the device can experience forces or movements that might push it loose or make it easier to pull out unintentionally. To prevent this, the rule requires an extra fastener that isn’t released by simply tugging on the device. This extra securing method (like a screw or locking device) keeps the plug‑in overcurrent device or main lug assembly firmly in place, even under back‑fed conditions. The other options don’t fit because the requirement isn’t about phase count or voltage level alone, and there is a specific condition (back fed) that triggers the need for an additional securing fastener.

The key idea is safety in back‑fed installations. When a panel can be back‑fed—power entering the panel from the load side or from a source not connected to the usual line side—the device can experience forces or movements that might push it loose or make it easier to pull out unintentionally. To prevent this, the rule requires an extra fastener that isn’t released by simply tugging on the device. This extra securing method (like a screw or locking device) keeps the plug‑in overcurrent device or main lug assembly firmly in place, even under back‑fed conditions.

The other options don’t fit because the requirement isn’t about phase count or voltage level alone, and there is a specific condition (back fed) that triggers the need for an additional securing fastener.