A chain should be replaced when its length becomes _______ longer than the original length.

A chain should be replaced when its length becomes 3% longer than the original length because this percentage indicates a significant amount of wear and elongation that can affect the performance and safety of the chain. Chains, particularly in mechanical applications, are subjected to various forces and stresses that can lead to stretching over time. When the wear exceeds this 3% threshold, it typically means that the integrity of the chain has been compromised, increasing the risk of failure during operation.

Replacing a chain at this point helps maintain optimal performance and safety, ensuring that the associated machinery continues to operate effectively without the risk of malfunction, which could arise from excessive wear. This standard aligns with best practices in mechanical maintenance, ultimately promoting longevity in the equipment and reducing overall maintenance costs.