Belt drive slip under load is most likely caused by which condition?

• A. Insufficient belt tension
• B. Worn belt
• C. Misalignment
• D. Excess belt tension

Answer: (A)

Belt drive slip under load happens because the belt must grip the pulley to transmit the required torque, and the grip comes from friction, which depends on how hard the belt is pressed against the pulley. When belt tension is too low, the contact pressure is insufficient, so the belt cannot provide enough friction to transmit the load and it slides on the pulley. A worn belt or misalignment can contribute to slipping or abnormal wear, but the most direct and common reason for slipping under load is not enough belt tension. Excess tension tends to increase grip but can cause other problems instead of causing slip.