Table of Contents
A service line can be defined as follows;
1). A L.T (low tension) line which is used to provide electricity from an electric pole up to the energy meter installed on the premises, is called a service line.
2). A-line, which is mounted between an electric pole and a consumer’s energy meter, is called a service line
3). Service line is a type of line, which supplies electric energy from the supplier’s lines to the consumer’s premises.
4). A-line through which a consumer’s installations are connected directly to the distribution lines is called a service line
5). A-line or cable which connects a supplier’s (e.g., WAPDA) distribution lines to the consumer’s wiring system via an energy meter, is called a service line.
The electrical power is supplied through the transmission lines from the generating stations or sub-stations to different cities and from there to the consumers for ordinary applications via the distributors or distribution lines. The consumers receive this power through a service line from the distribution lines (i.e., the consumer’s wiring or installations are connected directly with the distribution line through a service line). For domestic loads, a single-phase supply (220 – 250 volts) whereas for the industrial loads, a three-phase supply (380 – 440 volts), is provided. The service line used to get a single-phase connection tends to be a 2-core cable (one core for phase while the other for neutral), above which there is insulation covering of PVC (Poly Vinyl Chloride) or T.R.S (Tough Rubber Sheath). As a three-phase supply is normally provided to huge buildings or industries through a service line, therefore a four-core cable or service line is used at such places instead of a two-core cable. This four-core service line consists of red, yellow, blue, and black colors insulated covers, wherein red, yellow, and blue colored covers are used for the three supply phases, whereas the black color insulation cover functions as a neutral. It must be remembered that the service line should always be used according to the load requirements of the building.
Types of Service Lines
The following two types of service lines are used in a single- story and multi-storeyed buildings;
1). Overhead Service Line
2). Underground service Line
Overhead Service Line
If an overhead conductor has been used as a service line, this type of service line is called an overhead service line. In other words, if the supply line leading from an electric pole to the energy meter fitted in a building for providing electricity to a consumer’s installations, is set at a specific or a proper height, such a line is termed an overhead service line. The overhead service line or cable is tied with the L.T conductor of the pole through a clamp. Then this cable is fastened above a metallic wire and brought to the entrance passage of the consumer’s building. The purpose of a fastening cable above a metallic wire is to provide support against an expected sagging of the cable. Another advantage of a metallic wire is that in the case of a road crossing, a cable can be put at a reasonable height through it to avoid traffic disruption. Then, the cable is passed through a galvanized iron (G.I) pipe having a reasonable diameter and brought up to the energy meter fitted in the building. In figure 2.1, an overhead service connection has been illustrated.
To get overhead service connection, different sized all-aluminum stranded conductors (AAC), aluminum conductor steel reinforced (ACSR), or hard-drawn copper conductor (its application is very low nowadays due to being costly) are used according to the load of the consumer. In the case of copper conductor, the minimum size that tends to be used is 10SWG, provided the load does not exceed 1-kilo watt (1KW). If the load does not exceed 2.5 KW, then households, as well as commercial consumers, are supplied through an 8SWG copper conductor or 13.9 square millimeter size AAC or ACSR conductor. To connect a power load of up to 12 KW with the supply, a 6SWG copper conductor or 19.4 square millimeter AAC or ACSR conductor is used. The aluminum core PVC cables or weather-proof cables are used for cable service connection.
Figure 2.1 – Overhead service connections
Methods of Installation of Overhead Service Lines
The following methods are adopted for the installation of overhead service lines;
For High Roof Building or Multi-Storey Building
If the roof of any building is very high or if a building consists of more than two storeys, for this purpose a service bracket is firmly fixed onto the wall at a suitable height for installation of the service wire. On this service bracket, shackle style or pin type insulators are then mounted, the number of which depends on the number of incoming wires (an iron piece made of mild steel, which has been bent at a certain angle, is called a steel bracket). In the case of a common service connection or a single-phase connection, their number uses to be two, whereas, in a situation of power service connection or a three-phase connection, their numbers tend to be four. According to the rules, the vertical distance between the insulators must be 35 centimeters while the distance from the side should be 30 centimeters. The phase and neutral wire are always fetched from the nearest service pole and these are connected to the insulators fitted on the service bracket. The earth wire is joined with angle iron through an eye bolt. Thereafter, a weatherproof or PVC cable (which is known as a service cable) is tightly annexed to the conductors (i.e., overhead service line) through the connectors. Then, this cable is passed into an appropriately sized galvanized iron (G.I) pipe or conduit and carried to the service board. This has been illustrated in figure 2.2. The open-top mouth of the G.I pipe should be bent slightly so that rainwater does not enter the pipe. In figure 2.3, an alternative method for providing service mains has also been illustrated, wherein shackle insulators have directly been installed on walls instead of the service bracket.
Figure 2.2 – Service line connection with angle iron bracket for a double-story building
Figure 2.3 – represents an alternative method of providing service mains
For low Roof or Single Storey Building
If the roof of a building is low or the height of any building is substantially low, then the service bracket is not fitted directly onto the wall, because by doing so, the difference between the power conductors and earth will not be according to the electricity rules. Under such a situation, roof pole connection or G.I pipe connection are done. In the case of a roof pole connection, an appropriately sized strong steel tube, which is called a pole, is fitted. This has been illustrated in figure 2.4.
Alongside a steel pole or roof pole, arms are fitted length-wise, on which insulators have been mounted. The height of the roof pole should not exceed 3 meters otherwise tensile strength of the wires tied along with it, will increase. To reduce the power of this tensile strength, this pole is tied to the roof through a steel rope for providing it strong support.
In the case of the G.I pipe connection, the lower end of a suitably heightened galvanized iron (G.I) pipe is installed on the wall through clamps. As such, a pipe is thrust above the roof surface to a reasonable extent. However, the height of the pipe from the roof should not exceed 3 meters. So that tensile strength on G.I pipe, resulting from wires, does not cross a safe limit.
In order to provide support to a G.I pipe, a stay wire is also fastened with it, the other end of which is installed within the roof. In figure 2.5, the service line connection for a one-story building with a G.I pipe has been illustrated. A G.I wire has been tied between the top end of the G.I pipe and pole through an eye thimble, along which ring insulators are fitted at equal distances. The bare conductors of a service line are joined with these insulators. One end of the PVC pipe is connected to this service line, while its other end is carried up to the service board through the G.I pipe.
Figure 2.5 – Service line construction with G.I pipe to a single-story building
Weather Proof Cable Method
In this method of installation of the overhead service line, weatherproof cable or PVC cable is fastened with a G.I wire through clips, existing between the service pole and building. Then it is carried directly to the building and from there it is fixed on a wooden batten or passing it inside a G.I pipe, carried up to the service board. If the building has more than one storey, then one end of the 8SWG size G.I wire is tied to the service pole, while its other end is fastened to an appropriately heightened eye screw bolt fitted on the building wall. Then, the weatherproof cable is tied with this G.I wire through clips and it is carried up to the building. From there this cable is passed through the G.I pipe until it reaches the service board.
Underground Service Line
If an underground cable has been used as a service line, such a service line is called an underground service line. In other words, if the supply line from an electric pole through an energy meter in a building for the supply of electricity to the consumer’s installations, is spread underground, such a service cable line is called an underground service line. In figure 2.6, an underground service cable has been illustrated.
Figure 2.6 – service main by underground cable
The importance of underground mains increases at a time when the owner of a building fears that the beautification of his building could be at risk through the supply of an overhead service connection. Moreover, if several buildings are constructed side by side, it is always convenient to provide service connections to all these buildings in such a fashion that the service main is carried underground through a service pole to the main board of the building and then the main board of the second building is provided supply from the main board of the first building. Similarly, the main board of the third building is looped with the main board of the second building, as has been illustrated in the figure.
The Underground Cable Service Connection
The underground cable is generally used when the consumer is required to be supplied more than 25KW of power. For spreading the underground service line, an appropriate size cable box is installed on the service pole. For carrying cable from this cable box to another cable box fitted on the service board, the first cable is fetched onto the earth by passing it through the G.I pipe, which has been fitted on the pole with the help of clamps. Then, the cable is stretched into a one-meter trench dug into the ground from the pole base up to the building. After stretching the cable in the trench, it is filled up with sand and then the trench is closed from above through bricks. Sometimes, this service cable is passed in the underground trench inside G.I pipes, so that cable remains protected against mechanical shocks.
Remember that for spreading underground cable, a sound-insulated typed cable should be used, so that it does not get out of order soon. After stretching the cable underground, this cable is carried inside an appropriately sized G.I pipe up to the service board, so that cable remains shielded against external perils. In figure 2.7, the installation of an underground service cable has been illustrated.
Material Required for Overhead Service Line
|S. No||Nomenclatures||S. No||Nomenclatures|
|1.||Connector||9.||Single-Phase or Three-phase Service Mast Pipe|
|2.||Eye Screw Bolt||10.||Wall Clamp|
|3.||Weather Proof PVC Insulated Twin or Four Core Aluminum Cable||11.||Reg Bolts for Clamp Fitting|
|5.||Steel Clips||13.||Wooden or Plastic Dowels|
|6.||Pole Clamp with Thimble||14.||Screws for Meter Board|
|7.||Bush for G.I Pipe||15.||Single-phase or Three-phase Energy Meter|
|8.||Pipe Clamp||16.||Meter Board|
Next Topic: Types and Objects of Substations
Previous Topic: Electrical Installations
For electronics and programming-related projects visit my YouTube channel.