For a 480 V, 3-phase, 60 Hz air compressor, which safety switches are permitted as the disconnecting means?

For a 480 V, 3-phase, 60 Hz air compressor, which safety switches are permitted as the disconnecting means?

• A. I or II or III
• B. II only
• C. I or III only
• D. III only

Answer: (B)

The essential idea is that the disconnecting means for a motor load must be a listed device specifically permitted for motor disconnects, and it must be rated for the circuit voltage, readily accessible, and capable of being locked in the open position. For a 480 V, 3-phase air compressor, the only option that meets these requirements is the motor-disconnect switch that is listed for this use and rated for 480 V with lockout capability. The other options fail to meet one or more of these critical criteria (not a listed motor-disconnecting device, or not rated for 480 V, or not lockable), so they aren’t permitted as the disconnecting means.

The essential idea is that the disconnecting means for a motor load must be a listed device specifically permitted for motor disconnects, and it must be rated for the circuit voltage, readily accessible, and capable of being locked in the open position. For a 480 V, 3-phase air compressor, the only option that meets these requirements is the motor-disconnect switch that is listed for this use and rated for 480 V with lockout capability. The other options fail to meet one or more of these critical criteria (not a listed motor-disconnecting device, or not rated for 480 V, or not lockable), so they aren’t permitted as the disconnecting means.