They are typically one or two inches in diameter. A shield wire is a smaller wire located at the top of the building. The shield wire is intended to protect the power line from lightning strikes and may also house fiber optic communication cables. Power lines are usually made out of aluminum because of their lightweight and resistance to corrosion when exposed to weather conditions.
The distance between a transmission line and its support structure should be enough to prevent people from coming into contact with it. This is usually about 20 feet for high-voltage lines and 50 feet for low-voltage lines. Transmission lines are often set on poles or towers, which provide more space above them for other wires or equipment.
Transmission lines are usually divided into three classes according to their voltage: 120 volts or less, 125 to 135 volts, and 140 volts or higher. Lines carrying voltages below 69 volts are called low voltage (LV) and can usually be handled safely by a person if they are not cut off from electricity for an extended period of time. High-voltage (HV) lines are those that carry voltages of 70 or more. These should never be touched without protective gear because of the risk of electrical shock or death.
The ground wire is at the top of the cable, while the remaining (1 or 3 lines) are phase cables. Its sole purpose is to defend against lightning strikes. They protect the line by intercepting lighting strikes before they reach the current-carrying wires below. That is why they are frequently composed of steel. The term "grounded conductor" is often used to describe this type of wire.
In addition to being charged by lightning, power lines are also charged by wind. Strong winds can cause wires to vibrate, which in turn can cause trees to fall into adjacent property or even hit nearby buildings. This is called "wire stress". If a tree falls on a branch that holds one of these conductors, it could cut off its supply of electricity.
To prevent this from happening, all lines are equipped with protective devices called "indicators". These are small metal disks that rotate when voltage is present. They indicate this fact by turning red or yellow. If a tree falls onto a live line, the indicator will stop working and a driver will need to travel to the scene to check for any fallen trees or other damage.
Power companies try to keep their lines clear of vegetation to help avoid this problem in the first place. But if you are a landowner and want to reduce the risk of damage to your tower or lines, you should avoid planting trees within 10 meters (33 feet) of an electrical line.
Transmission lines are always designed with three conductor sets, plus a tiny wire or two at the top of the building for lightning protection. The three conductors carry current from the line side of any transformer to the building side, where they are routed through the house wiring to individual outlets and lights. The extra wires provide a second path in case of damage to one of the main lines.
The number of transmission lines depends on the type of transmission system used. On power lines this usually equals the number of circuits needed to service the premises. For telephone lines it is usually just one pair.
In general, the more circuits needed to serve the premises, the more transmission lines there will be. But even if only one circuit is needed, there will still be a single transmission line.
The amount of space taken up by transmission lines is not significant. A typical household circuit has up to 15 wires inside it, most of which are bare copper strands about an inch (25 mm) in diameter. Transmission lines, on the other hand, can be hundreds of feet long and made out of aluminum or steel, so their overall size is not important.
What does affect how they are laid out is the need to avoid interference between different services.
Grey/Grey 6381Y Cable 25mm sq. Power Cable with Dual Insulation
|Nominal Thickness of Insulation mm||1.4|
|Nominal Overall Diameter mm||11.5|
|Nominal Weight kg/Km||307|
|Maximum Diameter of Wires in Conductor mm||0.41|