Motor Controls

Distribution Systems 221

Distribution Systems 221 describes power distribution systems and their components. Distribution systems are integral parts of motor control systems because they consist of all generators, transformers, wires, and other devices used to transport power from the source to end use. Generating stations house generators that are linked together in parallel circuits to create power. Transformers step up and step down voltage. Substations house transformers and provide a safe point to cut the power.

Understanding the ways in which electricity is distributed and how to work safely with distribution systems is an essential part of working within motor controls. After taking this course, users will be able to describe how power enters a facility and is distributed to electrical equipment, as well as best practices for safely working with electrical power distribution systems.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 18

  • Language English


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Course Outline
  • Distribution Systems
  • Distribution System Components
  • Types of Distribution Systems
  • Distribution Systems Review
  • Generators
  • Transformers
  • Three-Phase Power
  • Wye Connections
  • Delta Connections
  • Phase Connections
  • Generators, Transformers, Power, and Connections Review
  • Substations
  • Switchboards
  • Panelboards
  • Motor Control Centers
  • Busways
  • Distribution System Maintenance
  • Distribution System Components and Maintenance Review
  • Describe distribution systems.
  • Identify the different components of a distribution system.
  • Describe different types of distribution systems.
  • Describe revolving field generators.
  • Describe transformers.
  • Describe three-phase power.
  • Describe wye connections.
  • Describe delta connections.
  • Describe the different phase connections in distribution systems.
  • Describe substations.
  • Describe switchboards.
  • Describe panelboards.
  • Describe motor control centers.
  • Describe busways.
  • Describe distribution system maintenance.
Vocabulary Term


Alternating current. Electrical current that reverses direction at regularly recurring intervals of time. AC usually reverses direction 60 times per second.

alternating current

AC. Electrical current that reverses direction at regularly recurring intervals of time. Alternating current usually reverses direction 60 times per second.


A component in generators that has coils wound around it. Armatures in revolving field generators are stationary.

branch circuits

The part of a distribution system that consists of webs of wires that extend from sets of outlets. Branch circuits are located between the final overcurrent protection devices and the load being powered.


The network of conductors that is housed in a busway. Busbars supply power to different areas in buildings.


An enclosure in a distribution system that allows power to be supplied to any area of a building from a single location. Busways use elbows, tees, and crossings that fit together in various ways to direct electricity in different directions to the desired destinations.

center tap

The point where all three windings are connected to each other in a connection in order to create a neutral line. Center taps can be used in both delat and wye connections.

circuit breakers

A switchgear with a bimetallic strip that bends and trips a switch to open a circuit. Circuit breakers detect excess current to prevent overheating.


A wire that allows for the easy flow of electricity. Conductors may also be called lines.

copper loss

A decrease in current due to the resistance that it encounters when flowing through conductors. Copper loss can be minimized with the use of transformers.


The iron or steel center of the transformer. The core provides a controlled path for current to travel.


The flow of electricity into a circuit. Current moves through distribution systems in conductors.


The time it takes for alternating current to flow, pause, reverse direction, and then pause again. Cycles are measured by phases.


A wire connection where three windings come together end-to-end to form a closed loop. Delta connections have equal phase and line voltages.


A phase connection where both the primary and secondary windings are connected to form a triangle. Delta/delta connections are used in large transformers with low voltage.


A phase connection with the primary winding connected as a delta and the secondary connected as a wye. Delta/wye phase connections link generators to transmission lines.

digital multimeter

DMM. A device that measures voltage, current, and resistance. Digital multimeters are used for electrical maintenance in a distribution system.

direct current

DC. Current that flows in a single direction. Direct current is the less common form of current.

disconnect switches

A switchgear operated manually or automatically that is flipped to open a circuit. Disconnect switches are used to prevent or stop overheating.

distribution substation

Substations that include switchgears and transformers that step down voltage. Distribution substations are located near users and ensure that current is at a safe level for delivery.

distribution systems

An electrical circuit that provides power to specific end destinations. Distribution systems deliver electricity in the form of alternating current to user networks.

electric shock

The flow of electricity through the body. Severe electric shock can be fatal.

electrical output

The amount of electricity generated by a device or network. Electrical output can be adjusted by electricians.


A form of energy created by the movement of electrons. Electricity can be converted into light, heat, or motion.


A physical barrier designed to provide mechanical or electrical protection for components used in a system. Enclosures are used to house transformers.


Different parts that allow conductors to connect to one another. Fittings give a busway flexibility and allow electricians to easily change wiring in distribution systems.


A switchgear that has a component that melts and opens a circuit. Fuses detect excess current to prevent overheating.

generating stations

A building that houses linked generators. Generating stations produce great amounts of power.


A device that converts mechanical energy into electrical energy. Generators are the main power sources for distribution systems.

goes down

A phrase used to describe the failure to deliver electricity properly. A line or generator may go down, causing electrical delivery to stop.


Connected to an electrically neutral body that can absorb stray electrical charge. Wye connections must be grounded to avoid damaging electrical components.

grounded conductor

The extra wire in an electrical system that provides a low-resistance path for stray current. Grounded conductors, also called neutral wires, help distribution systems avoid being damaged when current is flowing.

interconnected system

A distribution system with multiple available power sources throughout the network. In interconnected systems, if one source goes down, a different source can be activated to continue service.


Sealed together in multiple layers of thin sheets. Transformer cores are constructed by laminated materials.

line voltage

The voltage present between any two of the conductors in a three-phase system. Line voltage is 1.732 times greater than phase voltage in a wye connection but the same as phase voltage in a delta connection.


A conductor that allows for the easy flow of electricity. Lines may also be called wires.


A component in a circuit that converts electricity into light, heat, or mechanical motion. Loads include light bulbs, appliances, and machines.

magnetic field

A force of attraction that surrounds current-carrying conductors and magnets. Magnetic fields rotate within armatures of generators to produce current.

magnetic induction

The use of magnets to cause voltage in a conductor. Magnetic induction begins in the primary winding of a transformer in an electrical distribution system.

main disconnect switch

A heavy, spring-loaded switch on a switchboard that cuts off power to a facility. Main disconnect switches are required by the NEC in switchboards with more than six switches.


Activities for the necessary care and repair of machines, such as the lubricating, adjusting, and replacement of parts. Maintenance requires time, labor, and money but results in savings.

motor control centers

A modular assembly designed to house motor controls. Motor control centers also contain networked control and protection devices.

National Electrical Code

NEC. The standard for minimum safe electrical installations. The National Electrical Code contains guidelines on how to wire and maintain electrical distribution systems.

network system

A distribution system with multiple power sources that are connected to each other to guarantee uninterrupted power. A network system is expensive, so it is only used when constant power is vital to a system.

neutral wire

A conductor that does not carry a charge. Neutral wires are connected to center taps in wye connections.

open delta

A phase connection that does not complete the triangle, using only two of the three sides. An open delta is used to provide power when only two of the three windings are working.

overcurrent devices

A component like a breaker or a fuse that protects circuits from the damage that excess current flow can cause. Overcurrent devices are housed in switchboards in distribution systems.


A single panel distribution cabinet that holds overcurrent protection devices. Panelboards are connected to switchboards in distribution systems.

parallel circuits

A circuit that contains multiple loads and multiple paths for the flow of current. Parallel circuits do not require all loads to be receiving power for other loads in the system to function.


The interval of time between two successive events. A period in electrical systems defines the amount of time it takes for AC in a conductor to complete a cycle.

personal protective equipment

PPE. Any clothing or device used to minimize exposure to hazards and prevent injuries. Personal protective equipment may include safety glasses, hard hats, and steel-toed shoes.


A measurement of the voltage in a single AC cycle. Phases account for the transfer of power within a network.

phase delay

The staggered amount of time it takes for different conductors to reach peak voltage. Phase delays are a regular part of AC cycles.

phase voltage

The voltage between any one conductor and the neutral wire. Phase voltage is greater than line voltage in wye connections.

power sources

Devices that are responsible for generating current. Power sources in distribution systems are often generators.

power station

A source of electricity for a distribution system. Power stations can be run with a wye/wye phase connection.

primary winding

The first collection of coils that current passes through in a transformer. The primary winding contains multiple thin wires that are wrapped into a coil.

radial system

A distribution system with a single power source. In a radial system, if one wire malfunctions, the entire circuit loses power.

reserve generator

A generator that is used to produce power in a system when the primary generator goes down. Reserve generators compensate for power loss without interrupting power delivery.

revolving field generator

A generator in which a magnetic field rotates between conductor-wound armatures. Most AC generators are revolving field generators.

secondary winding

The second collection of coils that current passes through in a transformer. The secondary winding contains fewer but thicker wires than the primary wrapped into a coil.

single-phase power

Electricity that is generated by one cycle of alternating current. Single-phase power is used to run devices in homes and small businesses.

step down

A phrase used to describe a decrease in voltage. A transformer can step down voltage for safe delivery to users.

step up

A phrase used to describe an increase in voltage. A transformer can step up voltage for quick travel in a circuit.


Any grouping of switchgears and transformers located near a source or destination being powered. Substations alter voltage levels and provide a point of electrical control.


A freestanding assembly of panels with measuring equipment and protective devices. Switchboards take large blocks of power from substations and break them down into smaller blocks for use within a network.


A control device that can make or break a circuit by closing or opening. A switch can be either manual, mechanical, or automatic.


Devices that protect the electrical equipment in a distribution system. Switchgears include disconnect switches, fuses, and circuit breakers that are used to de-energize equipment.


A wire connected to a specific point on a transformer's secondary winding. Taps allow the autotransformers to use different turns ratios to vary voltage.


Connecting points in circuits. Wires are attached to terminals and create electrical connections.

three-phase power

A continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large scale distribution systems.


Devices that transfer electrical energy from one circuit to another. Transformers step up and step down voltage.

transmission lines

Conductors that carry current in a distribution system. Transmission lines can be linked to generators using delta/wye phase connections.

transmission substation

A location that houses switchgears and transformers that step up voltage. Transmission substations are located near generating stations and help current to travel quickly and efficiently.

turns ratio

A comparison of the number of turns in the primary versus the number of turns in the secondary winding. Transformers step up voltage or step down voltage based on the turns ratio.


A measure of electrical pressure. Voltage is also referred to as electromotive force.


A conductor that allows for the easy flow of electricity. Wires may also be called lines.


A wire connection where three wires come togehter to form three distinct points that look similar to a star. Wye connections may use center taps.


A phase connection where the primary winding is connected as a wye and the secondary as a delta. Wye/delta connections are used to power single- and three-phase loads at the same time.


Phase connections where both the primary and secondary windings are connected as a wye. Wye/wye connections are used to stabilize power when a generator starts.