Video: Recognizing dangerous lines

This short video explains the different kinds of lines that are part of the distribution system: Medium voltage, low voltage and telecommunications—and the danger that they can pose.

Duration: 2 minutes and 32 seconds

Medium-voltage lines (750–34,500 V)

Medium-voltage lines (750–34,500 V)

Medium-voltage lines are usually located at the top of utility poles.

They are thin metal wires without an insulated sheath. They are mounted on insulators, which look like small porcelain bowls. They may look harmless and aren’t insulated, but these lines are extremely dangerous!

Medium-voltage lines come in several possible configurations. While there are usually three separate wires, there may be up to six. There may even be a single wire, but don’t be fooled: it’s just as dangerous!

Lethal hazard!

Make sure no person, tool or construction material ever comes within 3 m of medium-voltage lines.

Why aren’t medium-voltage lines insulated?

If these are the most dangerous lines, why aren’t they insulated?

For mainly practical and economic reasons, the surrounding air is relied on to insulate these lines. In fact, that’s why they are high up—and why you shouldn’t go near them or place anything near them. If they were insulated, they would be much bigger and heavier, and that would require bigger or more numerous poles. The lines themselves would be more visually intrusive and cost much more. For these reasons, medium-voltage lines are left bare, with no insulating sheath, all over the world.

Low-voltage lines (120–600 V)

Low-voltage lines (120–600 V)

Just below the medium-voltage lines are the low-voltage lines. These are the lines that connect houses to the grid.

The term “low-voltage” may suggest that these lines do not pose any danger. But that’s not the case. Even 120-V lines can transmit hundreds of amperes, enough to cause a serious accident.

These are the two most common configurations of low-voltage lines:

  • Two wires with a black insulating sheath, twisted around a bare metal wire
  • Three stacked wires with an insulating sheath

As a precaution, avoid any contact with these lines. Even though they have an insulating sheath, it may be cracked or damaged.


Less often, you may see three lines, stacked one above the other, without an insulating sheath. If you do, NEVER COME WITHIN 3 M OF THEM.

Telecommunications lines

Below the low-voltage lines are large cables covered with a black insulating sheath. These are telecommunications lines, used for telephone and cable service.

Telecommunications lines generally carry 12 V. They do not belong to Hydro-Québec and are not an electrical hazard. But never let anything lean on them.

Wondering about those bigger wooden support structures or metal towers?

You’re probably looking at a high-voltage line that transmits power over long distances.

Attention: The rules about this type of line are even stricter.

See the safety rules for transmission lines