Service drop

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A three phase 220Y400 volt service drop in China. Service drop.jpg
A three phase 220Y400 volt service drop in China.

In electric power distribution, a service drop is an overhead electrical line running from a utility pole, to a customer's building or other premises. It is the point where electric utilities provide power to their customers. [1] The customer connection to an underground distribution system is usually called a "service lateral". Conductors of a service drop or lateral are usually owned and maintained by the utility company, but some industrial drops are installed and owned by the customer.

Electric power distribution Final stage of electricity delivery to individual consumers in a power grid

Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment or household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level.

Utility pole column or post used to support overhead power lines and various other public utilities

A utility pole is a column or post used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It can be referred to as a transmission pole, telephone pole, telecommunication pole, power pole, hydro pole, telegraph pole, or telegraph post, depending on its application. A stobie pole is a multi-purpose pole made of two steel joists held apart by a slab of concrete in the middle, generally found in South Australia.

An electric utility is a company in the electric power industry that engages in electricity generation and distribution of electricity for sale generally in a regulated market. The electrical utility industry is a major provider of energy in most countries.

Contents

At the customer's premises, the wires usually enter the building through a weatherhead that protects against entry of rain and snow, and drop down through conduit to an electric meter which measures and records the power used for billing purposes, then enters the main service panel. The utility's portion of the system ends, and the customer's wiring begins, at the output socket of the electric meter. The service panel will contain a "main" fuse or circuit breaker, which controls all of the electric current entering the building at once, and a number of smaller fuses/breakers, which protect individual branch circuits. There is always provision for all power to be cut off by operating either a single switch or small number of switches (maximum of six in the United States, for example); when circuit breakers are used this is provided by the main circuit breaker.

Weatherhead

A weatherhead, also called a weathercap, service head, service entrance cap, or gooseneck (slang) is a weatherproof service drop entry point where overhead power or telephone wires enter a building, or where wires transition between overhead and underground cables. At a building the wires enter a conduit, a protective metal pipe, and the weatherhead is a waterproof cap on the end of the conduit that allows the wires to enter without letting in water. It is shaped like a hood, with the surface where the wires enter facing down at an angle of at least 45°, to shield it from precipitation. A rubberized gasket makes for a tight seal against the wires. Before they enter the weatherhead, a drip loop is left in the overhead wires, which permits rain water that collects on the wires to drip off before reaching the weatherhead.

Electrical conduit

An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purposes.

Fuse (electrical) type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit

In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby interrupting the current. It is a sacrificial device; once a fuse has operated it is an open circuit, and it must be replaced or rewired, depending on type.

Residential

North American

A 240/120 V split-phase service drop providing power to a residence in USA. The three wires from the utility pole enter through a weatherhead (top) into a vertical conduit, which routes them to the electric meter (bottom). From there they pass through the wall of the house to the electric panel inside. Residence service drop.JPG
A 240/120 V split-phase service drop providing power to a residence in USA. The three wires from the utility pole enter through a weatherhead (top) into a vertical conduit, which routes them to the electric meter (bottom). From there they pass through the wall of the house to the electric panel inside.

In North America , the 120/240 V split phase system is used for residential service drops. [2] [3] A pole-mounted distribution transformer usually provides power for one or two residences. The service drop is made up of two 120 V lines and a neutral line. When these lines are insulated and twisted together, they are referred to as a triplex cable which may contain a supporting messenger cable in the middle of the neutral conductor to provide strength for long spans. The neutral line from the pole is connected to a ground near the service panel; often a conductive rod driven into the earth. The service drop provides the building with two 120 V lines of opposite phase, so 240 V can be obtained by connecting a load between the two 120 V conductors, while 120 V loads are connected between either of the two 120 V lines and the neutral line. 240 V circuits are used for high-demand devices, such as air conditioners, clothes dryers, ovens and boilers, while 120 V circuits are used for lighter loads such as lighting and ordinary small appliance outlets.

Distribution transformer transformer that provides the final voltage transformation in an electric power distribution system

A distribution transformer or service transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer. The invention of a practical efficient transformer made AC power distribution feasible; a system using distribution transformers was demonstrated as early as 1882.

As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.

Phase (waves) position of a point in time (an instant) on a waveform cycle

In physics and mathematics, the phase of a periodic function of some real variable is the relative value of that variable within the span of each full period.

European

In many European countries and other countries that use European systems, three-phase service drops are often used for domestic residences. The use of three-phase power allows longer service drops to serve multiple residences, which is economical with the higher density of housing in Europe. The service drop consists of three phase wires and a neutral wire which is grounded. Each phase wire provides around 230 V to loads connected between it and the neutral. Each of the phase wires carries 50 Hz alternating current which is 120° out of phase with the other two. Several slightly different voltage standards have been used in the past as well: 220Y380, 230Y400 and 240Y415, with plans for future "harmonization" towards 230Y400. In this notation, the first number is the voltage between a phase wire and neutral, and the second number, after the "Y", is the line voltage (between any two-phase wires).

Three-phase

In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating current voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y). A wye system allows the use of two different voltages from all three phases, such as a 230/400 V system which provides 230 V between the neutral and any one of the phases, and 400 V across any two phases. A delta system arrangement only provides one voltage magnitude, but it has a greater redundancy as it may continue to operate normally with one of the three supply windings offline, albeit at 57.7% of total capacity. Harmonic current in the neutral may become very large if nonlinear loads are connected.

Other countries, such as the UK and Republic of Ireland, generally provide a single phase and neutral per house, with every third house on the same phase. In this case the available current is higher. Single-phase supplies with a supplier's fuse of up to 100 A are common, while the 3-phase domestic supplies are generally of lower current rating (often less than 50 A) per phase.

Commercial and industrial

Commercial and industrial service drops can be much bigger, and are usually three phase. In the US, common services are 120Y/208 (three 120 V circuits 120 degrees out of phase, with 208 V line-to-line), 240 V three-phase, and 480 V three-phase. 600 V three-phase is common in Canada, and 380-415 V or 690 V three-phase is found in European and many other countries. Generally, higher voltages are used for heavy industrial loads, and lower voltages for commercial applications.

Three-phase electric power Common electrical power generation, transmission and distribution method for alternating currents

Three-phase electric power is a common method of alternating current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads.

In North America where single-phase distribution transformers for service drops are the norm, three-phase service drops are often constructed using three single-phase transformers, wired in a Y configuration. This is called a transformer bank.

Underground

Service conductors for a customer may be run underground, from a padmount transformer to a customer's meter.

Related Research Articles

Alternating current electric voltage which periodically reverses direction; form in which electric power is delivered to businesses and residences; form of electrical energy that consumers typically use when they plug electric appliances into a wall socket

Alternating current (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

Mains electricity general-purpose alternating-current electric power supply delivered to homes and businesses, used by consumer for domestic appliances, televisions and electric lamps through wall outlets

Mains electricity is the general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to homes and businesses, and it is the form of electrical power that consumers use when they plug domestic appliances, televisions and electric lamps into wall outlets.

Single-phase electric power

In electrical engineering, single-phase electric power is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 kW in rating.

Single-wire earth return technology to supply energy by single wire where earth will serve as return conductor

Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line which supplies single-phase electric power from an electrical grid to remote areas at low cost. Its distinguishing feature is that the earth is used as the return path for the current, to avoid the need for a second wire to act as a return path.

Electrical wiring in North America follows regulations and standards for installation of building wiring which ultimately provides mains electricity.

In electrical engineering, particularly power engineering, voltage regulation is a measure of change in the voltage magnitude between the sending and receiving end of a component, such as a transmission or distribution line. Voltage regulation describes the ability of a system to provide near constant voltage over a wide range of load conditions. The term may refer to a passive property that results in more or less voltage drop under various load conditions, or to the active intervention with devices for the specific purpose of adjusting voltage.

A distribution board is a component of an electricity supply system that divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit in a common enclosure. Normally, a main switch, and in recent boards, one or more residual-current devices (RCD) or residual current breakers with overcurrent protection (RCBO), are also incorporated.

Split-phase electric power Type of single-phase electric power distribution

A split-phase or single-phase three-wire system is a type of single-phase electric power distribution. It is the AC equivalent of the original Edison three-wire direct-current system. Its primary advantage is that it saves conductor material over a single-ended single-phase system, while only requiring a single phase on the supply side of the distribution transformer.

An autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. In contrast, an ordinary transformer has separate primary and secondary windings which are not electrically connected.

Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks. It does not normally cover the transmission of electrical power to them.

Electricity meter

An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device.

In an electrical installation, an earthing system or grounding system connects specific parts of that installation with the Earth's conductive surface for safety and functional purposes. The point of reference is the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary considerably among countries, though most follow the recommendations of the International Electrotechnical Commission. Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.

High-leg delta

High-leg delta is a type of electrical service connection for three-phase electric power installations. It is used when both single and three-phase power is desired to be supplied from a three phase transformer. The three-phase power is connected in the delta configuration, and the center point of one phase is grounded. This creates both a split-phase single phase supply and three-phase. It is called "orange leg" because the wire is color-coded orange. By convention, the high leg is usually set in the center lug in the involved panel, regardless of the L1-L2-L3 designation at the transformer.

Amtraks 60 Hz traction power system

Amtrak operates a 60 Hz Traction power system along the Northeast Corridor between New Haven, Connecticut and Boston, Massachusetts. This system was built in the late 1990s and supplies locomotives with power from an overhead catenary system at 25 kV, 60 Hz. The system is also commonly known as the Northend Electrification, in contrast to the Southend Electrification that runs from New York City to Washington DC.

Low-voltage network

A low-voltage network or secondary network is a part of electric power distribution which carries electric energy from distribution transformers to electricity meters of end customers. Secondary networks are operated at a low voltage level, which is typically equal to the mains voltage of electric appliances.

References

  1. Carson Dunlop "Electrical Systems" Dearborn Real Estate, 2003 ISBN   0-7931-7932-7 page 24
  2. Vadari, Mani (2013). Electric System Operations: Evolving to the Modern Grid. Artech House. p. 11. ISBN   1608075494.
  3. Waygood, Adrian (2015). Electrical Science for Technicians. Routledge. pp. 228–230. ISBN   1317534913.