Electrical Design of Commercial and Industrial Buildings – Glossary


120/208-volt, 3-phase, 4-wire, wye system
A distribution system generated with three individual sine waves separated by 120 electrical degrees that are identified as phases A, B, and C. One leg of each of the three phase coils is electrically connected to the others at a common point, forming a wye, which when grounded, becomes the fourth wire (or neutral) in the system. This allows for each of the three individual phase voltages to supply 120 volts to the grounded point, while the line voltage across each of the phases produces 208 volts. The line-to-line voltages can supply both 208-volt 3-phase and 208-volt single-phase. Because the three individual phases each can supply 120 volts, this system is commonly used in commercial office applications where 120 volts is desired because the 120-volt loads can be balanced across each of the three phases.
277/480-volt, 3-phase, 4-wire, wye system
A distribution system generated with three individual sine waves separated by 120 electrical degrees that are identified as phases A, B, and C. One leg of each of the three phase coils is electrically connected to the others at a common point, forming a wye, which when grounded becomes the fourth wire (or neutral) in the system. This allows for each of the three individual phase voltages to supply 277 volts to the grounded point, while the line voltage across each of the phases produces 480 volts. The line-to-line voltages can supply both 480-volt 3-phase and 480-volt single-phase. This system is commonly used in commercial applications where 480 volts is required for machinery loads and in applications to serve 277-volt lighting loads.
A/B switching method
A dual switching method to control lighting that reduces the connected lighting load by at least 50 percent, maintains reasonably uniform illumination, and helps meet mandated lighting energy requirements.
American National Standards Institute (ANSI)
An organization that oversees the development of standards created by manufacturers throughout the industry to promote safety and other standards.
area category method
A lighting design method that designers can use to meet man-dated lighting energy codes. In this method, the designer assigns a maximum allowable watts per square foot level to specifically define areas to provide adequate luminance for the primary function of the occupancy type. This method allows for maximum power levels in any one space to be exceeded when other spaces can be designed at lower allowed levels. The net result is that total power used does not exceed the calculated maximum allowed value. (See also complete building method.)
balanced distribution
An electrical distribution system in which the ungrounded conductors carry equal currents. In distribution systems that also include a grounded conductor, the grounded conductor will carry the imbalance of the currents in the ungrounded conductors.
branch circuit
The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s) [100].
bypass switch
A switch installed to override any automatic lighting shut-off device (e.g., time clock).
C value (for conductors)
Multipliers that have been developed for conductors that are derived by including both the resistance and the impedance of a conductor (X/R) installed in electrical systems. These multipliers are used in short-circuit calculations and result in calculation of more accurate short-circuit current values.
color rendering index (CRI)
The ability of a lighting source to correctly represent an illuminated object in relation to natural daylight.
complete building method
A lighting design method used to meet mandated lighting energy codes by calculating the maximum allowable lighting power for a facility based on a maximum allowable watts per square foot value; a basic design method not suitable for areas with specialty lighting. (See also area category method.)
computer-aided design (CAD)
The use of computers and design software to aid in the design of drawings, objects, shapes, and other items.
construction plans
A complete set of building plans which can be made available to all relevant parties providing an estimate for or performing work on a given project.
continuous load
A load where the maximum current is expected to continue for three hours or more [100],
counter electromotive force (CEMF)
An induced voltage that results in a force opposite in direction to the applied voltage; in AC circuits with magnetic properties (such as motors and transformers), this induced voltage can cause the circuit current to lag the applied voltage, resulting in lower power factor values.
demand factor
The ratio of power consumed by a system at any one time to the maximum power that would be consumed if the entire load connected to the system were to be operating at the same time.
effective grounding path
A grounding path of low resistance that ensures, either through raceway methods or additional wiring methods, that the operation of protective devices will occur to isolate a faulted system and thus protect personnel from the dangers of electrical shock or explosion.
Electrical Apparatus and Service Association (EASA)
An organization that provides information and education about sales, service, and maintenance materials for motors, generators, and other electromechanical equipment.
equipment grounding conductor
The conductive path installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor, to the grounding electrode conductor, or to both [100],
equipment list
A developed table that lists details about the specialized equipment that is to be incorporated into a design plan.
foot candle
(fc) A measurement of illumination intensity. One foot candle is the intensity of light on a surface 1 foot from a lighting source of 1 candlepower.
general purpose branch circuit
A branch circuit that supplies two or more receptacles or outlets for lighting and appliances [100].
ground fault
A condition in which high levels of current could flow when an ungrounded conductor accidentally comes in contact with a grounded reference. (See also short circuit.)
grounding electrode
A conducting object through which a direct connection to earth is established [100],
grounding electrode conductor
A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or a point on the grounding electrode system [100].
home run
The raceway designated on a plan as the one that carries branch-circuit conductors back to the serving source (such as a panelboard).
Illuminating and Engineering Society of North America (IESNA)
An organization that works with manufacturers, designers, architects, consultants, electrical and building contractors, and suppliers with regard to lighting systems.
inrush current
A momentary high level of amperage flowing in a circuit such as those associated with motorized equipment loads.
isolated ground (IG)
An additional equipment grounding conductor that, when installed, provides for the grounding of equipment separate from a grounding method that uses an approved raceway method; typically used for electrically sensitive equipment in computer applications and medical facilities. When isolated grounding is provided through the use of receptacles, the receptacle must be identified on the design plan as “IG.”
lighting branch circuit
A branch circuit that serves only lighting.
lighting energy-saving devices
Devices such as multiple switches, time clocks, and occupancy sensors that can achieve lighting energy savings.
lighting fixture schedule
A document included with the lighting design plan that lists the specific information for the lighting fixtures in a facility.
lighting system
Components such as branch circuits, switching devices, and energy-saving devices that are associated with lighting fixtures and their control.
load calculations
A set of calculated values that determine the demand factor for a system and that reflects a more true value of power utilized at any one time compared to calculated values determined during design.
lumens per watt (lm/W)
The ratio of light output (lumens) to input power (watts).
luminance level
The amount of light projected on a work surface.
main disconnecting means
The main device that disconnects the supply conductors from all sources of supply.
manufacturer electrical specification sheet
Information provided by a manufacturer that lists specific details about the product; these specification sheets are often used to obtain information about motorized equipment and lighting fixtures.
multiwire branch circuit
A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system [100].
National Electrical Code (NEC)
Regulatory code published by the National Fire Protection Association (NFPA); also known as NFPA 70.
National Electrical Manufacturers Association (NEMA)
A trade association that provides standards for the electrical manufacturing industry including the generation, transmission and distribution, control, and end use of electricity.
occupancy sensor
A device that detects the presence of personnel in a space by passive infrared or ultrasonic methods; when used in a lighting system, the sensor switches lighting fixtures on and off as occupants enter or exit the space to help save energy.
Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, if it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload [100].
panel schedule
An illustration of key panelboard information showing how branch circuitry is distributed, number of phases, voltage, and size in amperage; panel schedules are completed by hand calculation or by computer software.
plan check engineer
An engineer who performs building and plan examinations for construction or alteration of industrialcommercial, and residential structures and determines compliance with applicable codes, laws, and regulations.
point-to-point method
A calculation method to determine the available short-circuit current values at any point in a system.
programmable lighting controllers
Microprocessor-based lighting controllers that can be programmed; their use results in greater lighting energy savings.
An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars [100].
Raceway legend
A table developed by an electrical designer that illustrates information about raceways installed for a project
receptacle outlet
An outlet where one or more receptacles are installed [100].
reflected ceiling plan
A plan that illustrates only the location of lighting fixtures and the ceiling type in which they are to be installed.
separately derived system
A premises wiring system whose power is derived from a source of electrical energy or equipment other than a service. Such systems have no direct electrical connection. including a solidly connected circuit conductor, to supply conductors originating in another system [100].
service entrance conductors
The conductors from the service entry point to the service main disconnecting means. These can be installed as part of an overhead-type installation or in underground conduits.
short circuit
A dangerous condition in which circuit conductors contact each other and reduce the intended ohmic resistance of the circuit; often referred to as a line-to-line or line-to-neutral short. (See also ground fault.)
short-circuit calculations
A set of calculated values that determine available short-circuit currents.
single-line diagram
A simple diagram (also called one-line diagram) that illustrates all the information and requirements of an electrical distribution system.
spacing criteria
Mounting height ratios provided by the lighting fixture manufacturer used in calculations to determine proper mounting distances between lighting fixtures (also called row and column spacing criteria).
step-down transformer
A transformer that delivers a different utilization voltage; typically used in commercial applications to lower a 480/277-volt service to 120/208 volts for office spaces.
An electrical cabinet, or cabinets (depending on the electrical requirements), that has provisions for the service entrance method, utility metering, and overcurrent protective devices that serve distributions to equipment.
transformer impedance rating
A voltage drop rating for a transformer given in a percentage (Z) of the full load voltage.
utility metering equipment
The components that make up the parts of an electrical cabinet used solely for the purposes of utility metering, such as kilowatt-hours/demand, meter testing points, and current transformers.
voltage drop
A loss of voltage on a conductor resulting from the length of the conductor, its resistance, and the amperage imposed on the conductor.