Key Project Terms: Electrical Systems (Building Systems Installation & Modifications)

The following is a list of useful terms to use when researching additional Emergency Backup Power System information on each of the topics discussed:


Alternating Current

Accessible (Equipment)

Not guarded by locked doors, elevation or other effective means

Accessible (Wiring Methods)

Capable of being removed or exposed w/out damaging building structure.

Accessible (Readily Accessible)

Capable of being reached for operation, renewal, or inspections w/out requiring those to who ready access to climb over or remove obstacles or to resort to portable ladders.

Adjustable Speed Drive System

Power conversion equipment provides means of adjusting speed of motor.


A device intended to provide protection from effects of arc fault recognizing characteristics unique to de-energize ct when arc fault detected.


Rating indicates maximum fault current (amps) that an OCPD (circuit breaker, fuse) will safely clear when a fault is applied at load side of OCPD.

Alternative Power Sources

One or more power production sources that may operate in parallel with the primary source(s) of electricity Gas – Gas is supplied to the system either as natural gas or other.


An automatic or non-automatic (manual) device for transferring one or more load conductor connections from one power source to another

Bonding Jumper

Reliable conductor to ensure required electrical conductivity between metal parts required to be electrically connected


A non-insulated conductor electrically connected to the source of supply and physically supported on an insulator providing a power rail for the connection to utilization equipment, such as sensors, actuators, A/V devices, low-voltage luminaire assemblies, and similar electrical equipment.


Combined heat and power refers to simultaneous generation of electricity and useful heating and power generating.


A substance, body, or device that readily conducts heat, electricity, sound

Coordination (Selective)

Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. For the purpose of this code to overcurrent protective devices shall be deemed selectively coordinated if their respective time-current characteristics curves do not intercept at a time of 0.1 seconds (6 cycles on a 60 Hz systems) or longer.

Current-Limiting Overcurrent Protective Device (OCPD)

A device that, when interrupting currents in its current- limiting range, will reduce the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having comparable impedance.

Effective Ground Fault Current Path

An electrically conductive path from the point of ground fault on the wiring system through normally non-current-carrying conductors, equipment, or the earth to the electrical supply source.

Electric Closet

Room designed for/dedicated to purpose of containing electrical distribution equipment as vertical risers, bus ducts, transformer, and panelboards.

Electrical (System) Work

Design, installation, alterations, replace, or repair of electric wires and wiring apparatus and other appliances used or to be used for the transmission of electricity for electric light, heat, power, signaling, communication, alarm and data transmission.

Equipment Grounding Conductor (EGC)

The conductive path(s) installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both.


All circuit conductors between the service equipment, the source of separately derived system, or other power supply source and the final branch- circuit overcurrent device.

Fire Pump

A pump used exclusively for fire protection.


Equipment used to convert mechanical energy into electricity.

Ground Fault

An unintentional, electrically conductive connection between an ungrounded energized conductor of an electrical circuit and the normally non–current carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

Interrupting Rating

The highest current at rated voltage that an overcurrent protective device is intended to interrupt under standard test conditions.

Kilo Volt-Amp kVA Electric Service

Is a measurement unit of apparent power (active power) in an AC electrical circuit/ equipment, equal to (√3 × the voltage x the current) ÷ (1000), feeding an electrical load.

To calculate the ampacity of electric service equipment rating in kVA, the maximum ampere ratings of all service switches shall be used in calculating the kVA. Service disconnecting mean supplying fire pump shall be calculated at 125 percent of the fire pump FLA.

Examples: total ampere rating of service equipment that are considered 1000 kVA are; over 1200 amps at 480V/ 3 phase, and over 2700 amps at 208V/ 3 phase.

Main Bonding Jumper (MBJ)/System BJ (SBJ)

The connection between the grounded circuit conductor and the equipment ground conductor at the service.

Neutral Conductor

A conductor intended to carry current under normal conditions.

Neutral Disconnect Link (NDL)

A device used to isolate the neutral busbars in a switchboard to allow testing and maintenance of the equipment..

Nominal Voltage

A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.

One-Line Diagram

An electrical one-line diagram is a representation of a complicated electrical distribution system into a simplified description using a single line, which represents the conductors, to connect the components. Main components such as transformers, switches, and breakers are indicated by their standard graphic symbol. The diagram provides an overall information on the electrical equipment up to the second downstream level of OCPD.

Optional Standby System

Systems intended to supply power to public or private facilities or property where life safety doesn’t depend on performance of system. Intended to supply onsite generated power to selected loads either automatically or manually.


A single panel/group of panel units designed for assembly in the form of a single panel, including buses, automatic overcurrent devices, and equipped with/ without switches for the control of light, heat/power circuits. A typical panelboard is designed to be placed in a cabinet/cutout box placed in or against a wall, partition, or other support and accessible only from the front. Construction shall be in accordance with UL 67 standards.

Point of Entry

The Utility’s Service Layout identifying the service characteristics and the point of service termination.

Property Line Box

The Utility installed service lateral from a street system to the property line or suitable sub-sidewalk space, which is used for service termination

Selective Coordination Study

An analysis to ensure the localization of an overcurrent condition to restrict outages to the circuit or equipment affected (or nearest equipment), accomplished by the choice of overcurrent protective devices and their ratings or settings.

Separately Derived System

An electrical source, other than a service, having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.


The conductors and equipment for delivering electric energy from serving utility to wiring system of premises served.

Service Conductor

The conductors from the service point to the service disconnect means.

Service End Box (SEB)

An enclosure for connection of service cables to a suitable permanently attached Copper/Aluminum bus detail 3 or more sets of customer cables.

Service Equipment (SE)

The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply..

Short Circuit

Unintended contact of components and consequent accidental diversion of current.

Short-Circuit Current Rating

Maximum short-circuit current an electrical component can sustain w/out the occurrence of excessive damage when protected with an OCPD.


A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets. Construction shall be in accordance with UL 891 standards.


An assembly completely enclosed on all sides and top with sheet metal (except for ventilation openings and inspection windows) and containing primary power circuit switching, interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both. Construction shall be in accordance with UL 1558 standards.

Withstand Rating

The maximum current that an unprotected electrical component can sustain for a specified period of time without the occurrence of extensive damage.

Key Points & Project Terms Categories

  1. Alterations

  2. Building Systems Installation & Modifications

  3. Construction Equipment

  4. Demolition COMING SOON!

  5. New Buildings COMING SOON!

  6. Renovations

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