While servicing a packaged rooftop unit with a direct drive blower motor, you remove the access panel to the blower compartment to enable electrical checks on the blower to be made. The blower load increases, resulting in:

While servicing a packaged rooftop unit with a direct drive blower motor, you remove the access panel to the blower compartment to enable electrical checks on the blower to be made. The blower load increases, resulting in:

• A. Lower-than-normal blower amperage
• B. Higher-than-normal voltage fluctuations
• C. Tripping of electrical elements
• D. High-than-normal blower amperage

Answer: (D)

When a motor faces a heavier mechanical load, it must produce more torque to keep moving. Providing that extra torque requires more electrical power, so the motor draws more current. In a direct-drive blower, the speed can dip a bit as the load increases, which reduces back-EMF and pushes current higher still. The net effect is a blower that draws higher-than-normal amperage. A lower amperage would indicate the load decreased; voltage fluctuations are not the direct, primary consequence of increased load here; and tripping would occur only if the current exceeded protection device limits, which isn’t the described outcome.

When a motor faces a heavier mechanical load, it must produce more torque to keep moving. Providing that extra torque requires more electrical power, so the motor draws more current. In a direct-drive blower, the speed can dip a bit as the load increases, which reduces back-EMF and pushes current higher still. The net effect is a blower that draws higher-than-normal amperage. A lower amperage would indicate the load decreased; voltage fluctuations are not the direct, primary consequence of increased load here; and tripping would occur only if the current exceeded protection device limits, which isn’t the described outcome.