Why Hydro-Québec removes vegetation from medium-voltage lines

We clear the area around medium-voltage lines to avoid any risk of serious electric shock, fire or damage to the power system and reduce the frequency and length of any service interruptions. Close to 40% of power outages are caused by branches or trees falling on distribution lines.

Video: Tree Branches in Contact with a Medium-Voltage Line

January 2015, freezing rain in southern Québec. Tree branches weighed down by ice come too close to a medium-voltage line and catch fire.

Running time: 8 seconds
Footage shot by a Hydro-Québec customer in Montréal.

Shock, fire and short-circuit hazards

Medium-voltage lines don’t have an insulating sheath: The air around them provides insulation. That’s why they need to be kept clear.

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 by starting a fire or, in some cases, causing an electric shock.

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

Strong winds can occur at any time of the year and may be combined with snow, freezing rain or thunderstorms. The risks for the power system are highest when there are leaves on the trees because they catch the wind.

July 2013, Outaouais. Strong winds topple several fragile trees onto distribution lines. Restoring service required a great deal of work.
January 1998, Saint-Lambert. After an episode of freezing rain, branches overhanging distribution lines cause substantial damage.

Freezing rain

Ice buildup on branches is a heavy weight that can make a tree or branch bend until it breaks. A tree or branch that falls on a power line can cause short circuits, damage and power outages.

Wet snow

A thick layer of wet snow can make conifers bend until they break or become uprooted, posing a number of risks for the power system.

March 2008, the Laurentides. A pine tree weighed down by wet snow falls onto a power line.