According to ASME B.30.2, the minimum number of wraps on the hoisting drum should not be less than how many, unless a lower limit device is provided?

The standard ASME B30.2 establishes guidelines for the safe operation and design of overhead hoists, specifically addressing the proper use of the hoisting drum. According to these guidelines, having at least two wraps of wire rope on the hoisting drum is critical for ensuring adequate safety and stability during operation.

This requirement serves several purposes. Firstly, having a minimum of two wraps helps to prevent slippage of the rope, which can occur if there is insufficient material for friction to keep the load securely attached. Additionally, it provides a redundant support system; if one wrap were to fail, the second wrap can help prevent the load from falling.

Moreover, the mention of a lower limit device indicates that if such a device is present — which automatically stops the machine to prevent over-wrapping or undue stress on the hoist — the minimum wrap requirement might be adjustable. However, without such a device, adhering to the two-wrap rule is necessary for maintaining safety standards across operations.