What is meant by underground cables?
Cable that is specially designed to be placed/buried directly beneath the surface of the earth or within the conduit and later used for communication, power distribution or any other intended purposes.
What is the function of underground cable?
Underground cables are employed for transmission and distribution of electric power where it becomes impracticable to make use of overhead construction.
What are the types of underground cable?
The high-voltage underground cables used on the National Grid system can be one of three types: direct buried, trough, or tunnel.
What are the advantages of underground cable?
Lower cost & simplified siting process in urban locales Underground lines can be installed in dedicated public thoroughfares with dense population, and don't require right-of-way acquisition. Since land acquisition can be a major cost for transmission projects, underground lines are often more economical.
What is underground cable advantages and disadvantages?
The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs. However, they are more expensive to manufacture, and their cost may vary depending on the construction as well as the voltage rating.
Which material is used in underground cables?
The principal insulating materials used in cables are rubber, vulcanized India rubber, impregnated paper, varnished cambric, and polyvinyl chloride.
What is the difference between underground and overhead cables?
Overhead electricity lines are usually held up by wooden poles or steel towers. Typically overhead lines are more common in rural areas as they are used to cover greater distances. Underground electricity cables are laid below the ground and are usually found in built up areas such as cities.
Which type of cable is used for underground service?
What type of cable is used for underground service connections? Low tension 3 ½ core cable – This kind of cable is utilize or used for underground service connections.
What is the name of underground cable?
Direct-burial cable is a special type of electrical wiring or cable that is designed to be buried in a trench underground.
What are the types of cables?
Cables are classified into 5 types depending upon their purpose as follows:Ribbon Electric Cables. It consists of multiple insulated wires running parallel with one another and is used for transmission of multiple data simultaneously. ... Shielded Cables. ... Twisted Pair Cables. ... Coaxial Cables. ... Fibre Optics Cable.
What are the 3 types of wires?
Three types of wire used are :live wire ( Red colour)neutral wire(Black colour)earth wire (Green colour)
What is underground cable?
Underground cables are used for power applications where it is impractical, difficult, or dangerous to use the overhead lines. They are widely used in densely populated urban areas, in factories, and even to supply power from the overhead posts to the consumer premises. Figure 1: Basic construction of an underground cable|image: 3.bp.blogspot.com. ...
What is S.L cable?
S.L Type screened cable. The S.L type cables construction is almost like that of the H-type, however, each of the insulated cores is covered separately with its own lead sheath. Unlike the H-type, the S.L screened cable does not have an overall sheath, however it has the armoring and serving.
What are the disadvantages of tangential cable?
Disadvantages: Since the electrical field in the three core cables is tangential, the paper insulation and the fibrous materials are subjected to the tangential electrical stresses. This stresses weakens the fibrous material as well as the resistance and dielectric strength for the insulation along the tangential path.
Why are paper belts only suitable for high voltages?
Under high voltages the air may be ionized and cause deterioration and breakdown of insulation. For this reason, the belted cables are only suitable for voltages up to 11KVa and not higher. Due to the large diameter of the paper belt, bending the cable may lead to the formation of wrinkles and gaps.
How are 3 core cables insulated?
In a typical 3-core cable, each of the three cores is insulated by impregnated paper and covered by perforated aluminium foil or other metallic screen. The arrangement of the cores is designed to allow each of the three metallic screens to make contact with each other. The three cores are then wrapped around using a conduction belt made of copper woven fabric tape.
What is the material used to cover a belt?
This makes the cable to have a circular cross-sectional shape. A lead sheath is used to cover the belt hence protect it from moisture and provide mechanical strength.
How are underground cables classified?
The underground cables are classified in two ways; by the voltage capacity, or by the construction.
Why does underground cable burst?
A small-sized cable will most probably burst into flames because it cannot withstand the amount of electric current passing through it. If this happens, you’ll have to replace the cable. Replacement of an underground cable is more costly than typical PVC cables because you have to incur some expenditure in finding it. Thus, it is best to invest in the right size of cable regardless of the price. If you feel that underground cable suppliers are jerking up the prices unnecessarily, it is advisable to order it direct from ZW Cable.
What type of conductors are used in underground cables?
More importantly, you need to understand that underground cable types vary depending on their constitution? What exactly do I mean by cable constitution? This cable type comprises one, two, three, or four tinned-stranded copper conductors like typical PVC cables. Some manufacturers opt for aluminium conductors because they are cheaper than copper. Nonetheless, it is always advisable to go for cables made of copper conductors.
What is the voltage of an underground cable?
As per their voltage capacities, underground-type cables are generally classified as low-voltage wires for operating voltage up to 1 kilovolt and high-voltage cables for operating voltage up to 11 kilovolts. Other vital factors that you ought to consider when choosing an ideal underground power cable include;
What are the two types of underground wires?
As I mentioned earlier, there are two primary types of underground cables: high voltage and low voltage cables. Logically, each kind is suitable for particular applications. Logically, low voltage cables are ideal for applications that require minimal amperage. The most common low-voltage underground wires include;
How long does underground power last?
Essentially speaking, a quality underground power cable can last for several years without damage. This is why it is constantly advisable to consider the quality of the wire rather than the cable price. Unfortunately, most of us naively go for cheaper cables at the expense of quality. Instead of settling for the most inexpensive wire, it would be best to seek guidance from your local electrician on the best affordable underground cable type that suits your needs.
Why do people need to locate underground cables?
However, as I indicated earlier, an underground cable can withstand various external adversities, including heat and any other harsh conditions that may lead to its damage. In addition, an ideal cable choice can withstand the current that passes through it and any mechanical risks.
How many volts does a low voltage cable need?
What is the variance between these types of cables? Well, a low voltage cable is suitable for applications that require up to 1000 volts. So, if you intend to carry out applications that involve extreme voltage, a 15 kV underground cable may come in handy.
What is aerial cabling?
Aerial cabling can easily obstruct a property’s view as well as diminish the curb appeal and overall value of a property, whether that be a home or a business. Underground cabling ensures that the cables are completely out of sight and unobtrusive to any property.
Why are aerial cables so vulnerable to damage?
By being exposed to the elements and nature , aerial cables are more vulnerable to damage. A tree branch could fall, a car could hit the poles, heavy snowfall can weigh the cables down, or a squirrel could chew on the wires. Risking this damage means you also risk facing costly repairs and upset customers with no power or communications in their buildings. Underground cabling is the best choice for ensuring that your cabling will work regardless of weather conditions or unpredictable events.
What is underground cabling?
Underground cabling places fiber-optic cables out of sight and protects people from safety risks. When installing new power lines and utility cables, you have two choices: underground cabling or aerial cabling. Unless specific conditions prevent you from doing so, underground cabling is often the more beneficial choice for your cable installation.
Why are underground cables so popular?
Underground cables are popular in densely populated areas where space is precious. Additionally, when installed underground, cables require a narrower band of land than aerial cables would require.
Do tall buildings need underground cabling?
Downtown areas with tall buildings often require underground cabling, as underground cables are less exposed and therefore less dangerous than overhead cables, as well as less of an eyesore.
What are the other parts of cable?
Other parts of cable, just protect the conductor and sheath from mechanical injury or chemical attack. This does not mean that, they are not important. Bedding, Armouring and Servings are very important parts of cable else cable won’t work as its insulation will degrade.
What conductors are used in underground cables?
The conductor used in underground cable shall be tinned copper or aluminum conductor of high conductivity. Stranding is very important to provide flexibility and increase current carrying capacity. The size of conductor shall be sufficient enough to carry load current without heating and appreciable voltage drop.
What is armouring cable?
Armouring. Armouring is provided over the bedding to protect the cable from mechanical injury during its handling and lying. It consists of one or two layers of galvanized steel wire or steel tape. In some cable, armouring is not provided.
Why is underground cable bad?
Less voltage drop during normal operating condition and less chance of fault. But the main disadvantage of underground cable is its cost of installation. For higher voltage the cost of cable increases due to greater requirement of insulation as compared to overhead lines. Therefore, it is installed in area or localities where overhead lines cannot ...
What is bedding made of?
Bedding surrounds the sheath. It is made of fibrous materials like jute or hessian tape. The purpose of bedding is to protect the sheath from mechanical injury due to armouring. You can think it like a shock absorber.
What is insulation made of?
Normally the insulation materials are made of impregnated paper, varnish cambric or rubber mineral compound.
What is a three core cable?
The number of core or conductors in a cable depends upon its use. For example, a three core cable is used for three phase system. The conductors are made of tinned copper or aluminum and are stranded to provide flexibility.
How are cables insulated?
In such cables, the conductors (usually three) are bunched together and then bounded with an insulating paper ‘belt’. In such cables, each conductor is insulated using paper impregnated with a suitable dielectric. The gaps between the conductors and the insulating paper belt are filled with a fibrous dielectric material such as Jute or Hessian. This provides flexibility as well as a circular shape. As we discussed earlier (in Construction of Cables), the jute layer is then covered by a metallic sheath and armouring for protection. One particular speciality of this cable is that its shape may not be perfectly circular. It is kept non-circular to use the available space more effectively.
What is a metallic tape made of?
These three metallic covers are then grouped together in a metallic tape usually made of copper. A lead sheath surrounds this construction. The metallic covers and the sheath are grounded. The obvious advantage is the electric stresses are radial, not tangential and hence of lesser magnitudes.
Why do we use pressure cables?
For voltages beyond 66 kV, the electrostatic stresses in the cables exceed the acceptable values and solid cables become unreliable. This occurs mainly because voids are created when voltages exceed 66 kV. Hence, instead of solid cables, we use Pressure cables. Typically, such cables are either oil filled or gas filled.
What are the criteria for classification of underground cables?
Various aspects are taken into account while classification and these include: Number of conductors in the cable. Voltage rating of the cable. Construction of cable.
Why is dielectric strength kept non circular?
It is kept non-circular to use the available space more effectively. There are some limitations of such construction. Since the electric field is tangential, the insulation provided is stressed. As a result, the dielectric strength falls over time.
What is H.S.L. cable?
H.S.L. Type Cables: This type of cable is combination of H type and S.L. type cable. In these cables each core is insulated with impregnated paper and provided with seperate lead sheaths.
What is the maximum voltage handling capacity of high tension cables?
High tension cables: These have a maximum voltage handling capacity of 11 kV.
How to pull UF cable back through conduit?
Attach the end of the UF cable (or individual THWN wires) to the end of the fish tape, then carefully pull the cable back through the conduit. Having a helper feed the cable from one end as you pull on the fish tape makes this job much easier. Applying cable lubricant will make it easier to pull the cable.
How to lay UF cable?
Laying UF (underground feeder) cable directly into the ground. This is known as direct burial, and if you do this, the UF cable must be at least 24 inches below the surface of the ground, to minimize the chance of the cable being pierced by routine shoveling. Further, the vertical runs where the cable descends into the ground at the house side and emerges up from the ground at the outbuilding side must be housed in rigid conduit, usually PVC. At the bottom of the trench, a sweep fitting is attached to the ends of the vertical conduit, and the cable is snaked through the elbows and up into the conduit at both sides.
How deep should conduit be for running wire?
Running wire through rigid galvanized metal conduit. In this method, the conduit can be as shallow as 6 inches deep, and the individual conducting wires inside should have a "W" labeling to indicate they are waterproof. THWN-2 wire, for example, is a standard type for running through underground conduit. Use thick-walled conduit at least 3/4 inch ...
How many amps for overhead light?
For powering overhead light fixtures and one or two wall outlets in a garage: install one 15- or 20-amp 120 -volt circuit.
Can you run an underground circuit in a detached garage?
Extending electrical service to a detached garage or other outbuilding isn't much different than adding a circuit inside the house, with one important exception—running underground cable. If you are sufficiently confident of your wiring skills that you would feel comfortable adding an electrical circuit indoors, then running a circuit to a detached outbuilding is something you may be able to do yourself. But be aware that it involves work at the main circuit breaker panel to install and connect one or more new circuit breakers. Many people choose to have this kind of work done by a professional, and with good reason—work at the main service panel has the potential for very serious or fatal shock if you don't know what you are doing.
Can you fish through conduit?
But it can be difficult to fish cable through conduit, unless the conduit is at least 3/4 inch in diameter. Most electricians prefer to fish individual waterproof THWN conductors through conduit, simply because it is easier.
Can you extend electrical service to a detached garage?
Extending electrical service to a detached garage or other outbuilding isn't much different than adding a circuit inside the house , with one important exception—running underground cable. If you are sufficiently confident of your wiring skills that you would feel comfortable adding an electrical circuit indoors, ...
Why does voltage drop?
Since voltage drop is caused by the resistance of conductors, the more conductors you have, the greater the voltage drop. When it comes to underground wire, the longer the wire, the greater the voltage drop. Wire size is another factor: Smaller-diameter wires have more resistance than larger-diameter wires. Copper wire has lower resistance ...
How does voltage drop affect a circuit?
Voltage drop increases as the load on a circuit increases, and overloading a circuit contributes to excessive voltage drop. In other words, if you put too many loads on one circuit and exceed the standard 80 percent safe capacity (1,440 watts for 15-amp circuits; 1,920 watts for 20-amp circuits), you'll add unnecessary voltage drop.
How much voltage drop for a 120 volt circuit?
The following are the maximum lengths of cable you can use while still maintaining a 3 percent voltage drop for the given wire size (AWG) and circuit voltage. As an example, for a 120-volt circuit, you can run up to 50 feet of 14 AWG cable without exceeding 3 percent voltage drop.
Why do you need to increase the wire size of a cable?
However, if the cable run is long , as underground runs often are, you may need to increase the wire size to account for voltage drop — a loss of voltage in the circuit caused by the natural resistance in the wires.
Why is voltage drop a waste of electricity?
Voltage drop is also a waste of electricity because the energy is lost as heat rather than being available for use by the circuit devices.
What is the effect of voltage drop?
One effect of this resistance, also called impedance, is a loss of voltage.
What is underground wire?
Underground wire for a residential circuit usually is installed with underground feeder (UF) cable, which is rated for outdoor use and direct burial. Such an installation is typical when running a circuit to an outdoor location, such as a garage, shed or other outbuilding, or to a yard light or water feature.
What Is An Underground Cable?
What Are The Types of Underground cables?
- As I mentioned earlier, there are two primary types of underground cables: high voltage and low voltage cables. Logically, each kind is suitable for particular applications. Logically, low voltage cables are ideal for applications that require minimal amperage. The most common low-voltage underground wires include; A. STA Cable STA is an acronym th...
How to Find Underground cables?
- As I mentioned earlier, an underground cable is a safer alternative to an overhead cable. However, its downside is that you can easily forget the specific installation location. As such, they tend to present huge risks down the line, especially if you intend to do some landscaping work. Attempting to perform such tasks without pinpointing the exact location of the underground po…