Which of the following is a significant factor for tree-related outages?

The significant factor for tree-related outages is tree height relative to power lines. This is because the proximity of trees to power lines can lead to contact, especially during adverse weather conditions such as high winds or ice accumulation. Trees that grow too tall or are not appropriately managed can cause branches to interfere with power lines, leading to outages when branches fall or make contact with the lines.

In utility arboriculture, maintaining a safe distance between trees and power lines is crucial to prevent power outages and ensure safety. Proper pruning and management practices are necessary to mitigate risks associated with tree growth near electrical infrastructure.

While the other factors offered may seem relevant, they do not specifically address the direct cause of outages as effectively as tree height relative to power lines does. For instance, single-phase and 3-phase lines pertain more to the type of electrical distribution, but the height of trees directly influences the risk of interference with power lines. Poor maintenance practices can lead to problems but again relate indirectly to the significance of tree height in causing outages.