Electric shocks, fires and short circuitst
Medium voltage lines are not covered by insulating sheaths: The air around them provides insulation.
Vegetation and tree branches that are too close to medium-voltage lines can also cause short circuits, even without any direct contact. They can endanger people’s safety by starting a fire or causing an electric shock.
Video: Tree branches in contact with a medium-voltage line
January 2015, a day of freezing rain in the south of Québec: tree branches weighed down by the ice come too close to a medium-voltage line and catch fire.
Footage shot by a Hydro-Québec customer in Montréal
Risks related to weather events
Most power outages caused by falling branches or trees result from major weather events like strong winds, freezing rain and wet snow.
Strong winds can occur at any time of the year and may be combined with snow, freezing rain or rain. The risks for the power system are highest when there are leaves on the trees because they catch the wind.
Ice buildup on branches is a heavy weight than can make a tree or branch bend so much that it breaks. A tree or branch that falls on a power line can cause short circuits, damage and power outages.
A thick layer of wet snow can make conifers bend so much that they break or become uprooted, posing a number of risks for the power system.