Armoured cables and cables with an earthed metal sheath appropriate for use as a protective conductor may be buried directly in the ground without extra protection, with the exception of corrosion, which can be avoided by using a plastic covering. Surface-mounted wires can be attached to permanent constructions. Such wires should be kept away from water, heat sources, and any other source of heat or stress. They should be located out of reach and sight of children.
Cables should not be buried under roads or in underground channels because they will cause road damage or channel collapse.
The depth that cables should be buried is dependent on their purpose. Telephone lines should be buried at least as deep as the tallest plant that would normally grow between them. Power cables should be at least as deep as the maximum expected temperature of 45 degrees Celsius. If the cable is intended to carry electrical signals, then it should be buried as deep as possible while still allowing room for expansion and contraction of moisture inside the tube.
Telephone cables should be encased in PVC or polyethylene tubes about 1 inch in diameter. These can usually be bought pre-terminated (i.e., with connectors mounted on each end) from telephone company contractors. The cables should be placed in the tubes with the centerlines aligned and the ends of the tubes closed off with caps. The entire assembly should be lowered into the ground with the caps facing up.
Armored cables give the necessary protection and durability without the need of electrical conduit, elbows, expensive offsets, or conduit couplings. Metal-clad armor resists corrosion, making it acceptable for use in wet environments. Metal-clad cables can be cut with metal shears and will not kink or break like insulated cables when subjected to stress.
Metal-clad cables are used in construction projects for their durability and resistance to corrosion. They are also used by electricity providers as back up wiring for power outages. These cables can be found in public buildings such as schools, hospitals, government offices, and commercial buildings.
Metal-clad cables are available in different sizes, from one end connector to several hundred meters length. The thickness of the metal cladding varies depending on the application; usually it is between 0.5 and 1.5 millimeters thick. Armored cable is designed to be cut with a knife or metal shear. It is important to note that cutting metal-clad cable may cause a spark if not done properly. This type of cable should not be severed with an axe or hammer because this could lead to damage outside of the specified cut areas.
End connectors for metal-clad cables include special fittings called dead ends. These fittings are used to terminate lengths of cable.
A non-metallic sheathed cable is an assemblage of two or more insulated conductors with a non-metallic outer sheath that is moisture-resistant and flame-retardant. In addition to the insulated conductors, the cable may include an uninsulated or bare conductor of an allowed size for grounding reasons alone. The term "NM cable" is often used as a short-hand description for this type of cable.
Non-metallic sheathed cables are commonly used as feeders from electrical panels to other circuits within a building. They are also used to connect one panel or group of panels to another panel or group of panels. These connections are called branch circuits and should be performed using circuit breakers or fuse boxes. NM cables are designed to carry current up to about 20 amperes without overheating or breaking down. Cables used for higher currents need to be metal-clad instead.
Cables used for telecommunication systems must meet special requirements. These cables are called "telecomms" cables and they can be either fiber optic or copper wire. Fiber optic cables contain several strands of glass fibers surrounded by a protective coating. Copper wires are covered in thick layers of insulation and each layer is wrapped around the previous one until you get to the final layer which is only wrapped once or twice. This last layer serves as the conductive path for electricity.