Commercial Electrical Glossary

A plain-language guide for property managers, facilities directors, general contractors, and purchasing departments.

Power Distribution & Infrastructure

Amperage (Amps)

Amperage, expressed in amps (A), is the measurement of electrical current flowing through a circuit. Every electrical device consumes a certain amount of current, and every circuit has a maximum amperage capacity. Exceeding that capacity trips a breaker or blows a fuse. Determining the amperage required by new equipment or a planned expansion is an important early step in any facility electrical project.

Circuit Breaker

A circuit breaker is a safety device that automatically interrupts electrical flow when a circuit is overloaded or a fault occurs. Unlike a fuse, a circuit breaker can be reset after it trips rather than replaced. In commercial facilities, breakers are housed in distribution panels and sized to protect specific circuits. FSG's electrical service team handles breaker replacement, panel upgrades, and fault diagnosis.

Distribution Panel

A distribution panel, also known as a sub-panel or load center, receives power from the main service panel and distributes it to individual circuits within a section of a building. Large commercial facilities typically have multiple distribution panels fed from a central switchgear or main panel. FSG installs and upgrades distribution panels as part of broader electrical infrastructure projects.

Electrical Capacity Expansion

An electrical capacity expansion increases the total amount of power available to a facility by upgrading the service entrance, adding new panels, or installing additional feeders. Capacity expansions are typically driven by new equipment loads, building additions, EV charging infrastructure, or changes in facility use. FSG manages electrical capacity expansions for operational facilities with minimal disruption to ongoing operations.

Electrical Service Entrance

The electrical service entrance is the point where utility power enters a building, typically consisting of the service conductors, meter enclosure, and main disconnect. The service entrance determines the maximum voltage and amperage available to the facility. Upgrading the service entrance is required when a facility needs more power than the current infrastructure can deliver.

Feeder Circuit

A feeder circuit is a set of conductors that carry power from the main service panel or switchgear to a distribution panel or sub-panel. Feeders do not connect directly to individual loads; they supply power to the panels that then distribute it to branch circuits. Feeder sizing is determined by the total load demand of the distribution panel it serves.

Fuse

A fuse is a one-time overcurrent protection device that interrupts a circuit when current exceeds a safe level. When a fuse blows, it must be replaced rather than reset. Fuses are still found in older commercial facilities and in some specialty applications such as disconnect switches and motor circuits. Most modern commercial electrical systems use circuit breakers instead.

Load Balancing

Load balancing is the process of distributing electrical loads evenly across the available phases and circuits in a facility's electrical system. Unbalanced loads can cause overheating, reduced equipment life, and inefficient energy use. Load balancing is typically addressed during panel upgrades, new equipment installations, and service expansions.

Main Service Panel

The main service panel is the primary electrical distribution point in a building, receiving power from the utility service entrance and distributing it to branch circuits and sub-panels throughout the facility. It contains the main disconnect and the primary overcurrent protection devices. Panel replacement and upgrades are among the most common commercial electrical projects FSG performs. Learn about FSG's panel upgrade and service expansion capabilities.

Meter / Utility Meter

A utility meter measures the amount of electrical energy consumed by a facility and is the basis for utility billing. Commercial facilities may have a single meter or multiple meters for different tenants or cost centers. Smart meters provide interval data that can be used for energy management and load analysis. The meter is owned and maintained by the utility company, not the facility.

Panel Installation / Panel Changeout

A panel installation involves adding a new electrical panel to a facility to serve new loads or expand capacity. A panel changeout replaces an existing panel, typically due to age, damage, insufficient capacity, or a safety concern such as a recalled panel brand. Both involve de-energizing the affected circuits and coordinating with the utility for service disconnection where required. FSG's electrical contractor team handles panel installations and changeouts for commercial facilities of all sizes.

Switchgear

Switchgear is a collection of electrical disconnect switches, fuses, and circuit breakers used to control, protect, and isolate electrical equipment in medium- to large-scale commercial and industrial facilities. It operates at higher voltages and current levels than standard distribution panels and is typically found in the main electrical room of larger buildings, campuses, and industrial facilities. FSG installs and upgrades switchgear as part of industrial and large-scale facility electrical projects.

Transformer

A transformer is a device that changes electrical voltage from one level to another. Utility power is typically delivered at high voltage and stepped down by a transformer to the voltage levels used inside a building, commonly 120V, 208V, 240V, or 480V. Transformers are also used within facilities to supply specific voltage requirements for equipment. FSG's industrial and facility electrical services include transformer installation and replacement.

Voltage

Voltage, measured in volts (V), is the electrical pressure that drives current through a circuit. Commercial facilities typically operate at 120V for general receptacles and lighting, 208V or 240V for HVAC and larger equipment, and 277V or 480V for industrial motors and high-demand loads. Understanding the voltage requirements of new equipment is essential before installation to ensure the correct circuits and wiring are in place.

Watts / Kilowatts

Watts (W) and kilowatts (kW) measure electrical power, which is the rate at which energy is consumed. One kilowatt equals 1,000 watts. Watts are calculated by multiplying voltage by amperage (V x A = W). In commercial electrical planning, kilowatts are used to size panels, feeders, and service entrances based on the total connected load in a facility.

Electrical Construction & Project Types

Design-Build (Electrical)

Design-build is a project delivery method in which a single contractor is responsible for both the engineering design and the physical construction of an electrical system. This consolidates accountability and typically reduces project timelines compared to traditional design-bid-build delivery, where design and construction are handled by separate parties. FSG's electrical design-build services include engineering, CAD, BIM coordination, and construction.

Electrical Buildout / Tenant Improvement

An electrical buildout is the installation of a complete electrical system within a new or renovated commercial space, typically as part of a tenant improvement project. This includes panel installation, circuit distribution, device installation, and coordination with other trades. Tenant improvement electrical work is one of the most common commercial electrical project types for office buildings, retail spaces, and medical facilities. FSG performs electrical buildouts for tenant improvements across a wide range of commercial property types.

Electrical Capacity Expansion

See Electrical Capacity Expansion in the Power Distribution & Infrastructure section above.

Electrical Rough-In

Electrical rough-in is the phase of construction in which conduit, wiring, boxes, and other infrastructure are installed before walls are closed up. Rough-in work is inspected by the authority having jurisdiction (AHJ) before drywall or finishing materials are applied. Getting rough-in work right is critical because corrections after walls are closed are significantly more expensive.

Ground-Up Construction (Electrical)

Ground-up construction refers to electrical work on a new building from the foundation up, as opposed to renovation or retrofit work on an existing structure. It involves the complete design and installation of all electrical systems, from the service entrance through final devices and fixtures. FSG's electrical construction division handles ground-up commercial and industrial electrical projects.

Prefabrication (Electrical)

Electrical prefabrication is the process of assembling conduit assemblies, wire harnesses, panel boards, and other electrical components off-site in a controlled environment before delivering them to the job site for installation. Prefabrication reduces on-site labor hours, improves quality control, and accelerates project schedules. FSG's Propel Prefab program is one of the most developed electrical prefabrication operations in the country.

Service Relocation

A service relocation moves the electrical service entrance and associated infrastructure from one location on a building or property to another. This is commonly required during building expansions, site redevelopment, utility upgrade projects, or when the existing service location creates a code compliance issue.

Service Upgrade

A service upgrade increases the amperage or voltage capacity of a facility's electrical service entrance to meet growing power demands. Common triggers include adding EV charging stations, new manufacturing equipment, HVAC upgrades, or building expansions. Service upgrades typically require utility coordination and may involve temporary power during the transition. FSG's electrical contractor team manages service upgrades including utility coordination and permitting.

Temporary Power

Temporary power is an electrical supply installed to serve a construction site, special event, or facility in transition before permanent electrical infrastructure is in place or restored. It typically involves temporary panels, generators, and distribution equipment that are removed once permanent power is available. FSG's electrical services include temporary power solutions for construction projects and emergency situations.

Backup & Emergency Power

Automatic Transfer Switch (ATS)

An automatic transfer switch (ATS) monitors utility power and automatically switches a facility's electrical load to a backup generator when an outage is detected, then transfers back when utility power is restored. The ATS eliminates the need for manual intervention during a power failure. For facilities with critical operations, an ATS is an essential component of any backup power system. FSG installs automatic transfer switches as part of commercial generator and backup power projects.

Backup Power System

A backup power system provides electrical power to a facility when utility power is unavailable. It typically consists of a generator, automatic transfer switch, and distribution infrastructure sized to support critical loads. Backup power systems range from partial coverage of life-safety systems to full-facility standby power for uninterrupted operations. FSG's guide to backup power for commercial facilities covers sizing, fuel options, and transfer switch configurations.

Commercial Generator

A commercial generator is a diesel, natural gas, or propane-powered engine-driven alternator that produces electrical power during a utility outage. Generators are sized in kilowatts (kW) based on the loads they need to support. Commercial generators range from small units serving critical circuits to large standby systems that power an entire facility. FSG installs commercial generators including Generac and other major brands, with full transfer switch and commissioning services.

Emergency Power System

An emergency power system is specifically designed to supply power to life-safety loads during a utility outage, including emergency lighting, exit signs, fire alarm systems, and elevators. NEC Article 700 governs emergency systems in commercial buildings and defines specific requirements for transfer time, testing, and maintenance. Emergency power systems are distinct from optional standby systems, which serve non-life-safety loads.

Manual Transfer Switch

A manual transfer switch requires a person to physically switch a facility from utility power to generator power during an outage. Manual switches are less expensive than automatic transfer switches but require on-site personnel to operate. They are commonly used in smaller commercial applications or as a backup to an automatic transfer switch for non-critical loads.

Standby Power vs. Emergency Power

Standby power systems provide backup power to loads that are important to operations but not required for life safety, such as data centers, refrigeration, and manufacturing equipment. Emergency power systems are code-required and serve life-safety loads such as egress lighting and fire suppression. Both types may use generators, but they are governed by different NEC articles and have different performance and testing requirements.

UPS (Uninterruptible Power Supply)

A UPS is a battery-based device that provides immediate backup power to connected equipment when utility power fails, without the startup delay of a generator. UPS systems are used to protect sensitive equipment such as servers, medical devices, and control systems from power interruptions and voltage fluctuations. They are typically used to bridge the gap between a power failure and generator startup, or as the sole backup source for small critical loads.

Industrial & Facility Power

Dedicated Circuit

A dedicated circuit serves a single piece of equipment or load, with no other devices sharing the circuit. The NEC requires dedicated circuits for certain equipment such as HVAC units, refrigerators, dishwashers, and EV chargers. In commercial settings, dedicated circuits are also specified for sensitive equipment, high-demand machinery, and any load where interference from other devices could cause operational problems.

Motor Control Center (MCC)

A motor control center is a pre-assembled enclosure containing the motor starters, overload relays, disconnect switches, and control wiring needed to operate multiple electric motors from a central location. MCCs are standard in industrial facilities, data centers, water treatment plants, and large commercial buildings with significant motor-driven equipment such as pumps, fans, and compressors. FSG installs and commissions motor control centers as part of industrial and large-scale facility power projects.

Phase Power (Single-Phase vs. Three-Phase)

Single-phase power is the standard electrical supply for most residential and small commercial applications, delivering power through two conductors. Three-phase power uses three conductors and delivers power more efficiently for large motors, industrial equipment, and high-demand commercial loads. Most commercial and industrial facilities operate on three-phase power at the building level, with single-phase circuits distributed to general receptacles and lighting.

Power Factor

Power factor is a measure of how efficiently electrical power is being used in a facility, expressed as a value between 0 and 1. A power factor of 1.0 means all supplied power is doing useful work. Many commercial facilities have power factors below 1.0 due to inductive loads such as motors and transformers, which can result in utility demand charges. Power factor correction equipment can improve efficiency and reduce utility costs.

Surge Protection

Surge protection devices (SPDs) protect electrical equipment from voltage spikes caused by lightning, utility switching, or large equipment cycling on and off. In commercial facilities, whole-building surge protection is installed at the main panel, with additional point-of-use protection at sensitive equipment. Without adequate surge protection, voltage spikes can damage electronics, control systems, and motors.

Variable Frequency Drive (VFD)

A variable frequency drive is an electronic controller that adjusts the speed of an electric motor by varying the frequency of the power supplied to it. VFDs are used on pumps, fans, compressors, and conveyor systems to match motor speed to actual demand rather than running at full speed continuously. This can reduce energy consumption by 20 to 50% on applicable equipment and extend motor life by reducing mechanical stress.

Wiring, Conduit & Components

AFCI (Arc Fault Circuit Interrupter)

An arc fault circuit interrupter (AFCI) is a circuit breaker or outlet device that detects the electrical signature of an arc fault — an unintended electrical discharge that can ignite a fire — and automatically interrupts the circuit. AFCIs are required by the NEC in certain commercial and residential spaces where arcing in concealed wiring poses a fire risk. They are distinct from GFCI devices, which protect against shock rather than arcing. FSG's electrical service team can assess AFCI requirements during code compliance reviews.

Branch Circuit

A branch circuit is the portion of a wiring system that extends from the final overcurrent protection device, typically a circuit breaker, to the outlets, devices, or equipment it serves. Branch circuits are the individual circuits that power specific areas or pieces of equipment within a building. Each branch circuit is sized based on the amperage of the breaker protecting it and the anticipated load it will carry.

Conduit

Conduit is a tube or channel used to protect and route electrical wiring through a building or site. It is the most common type of raceway, a broader term for any enclosed pathway used to contain electrical conductors. Conduit comes in several types — EMT (electrical metallic tubing), rigid metal conduit (RMC), PVC, and flexible conduit — each selected based on the installation environment, code requirements, and physical protection needed. FSG's electrical construction teams install conduit systems for new construction, tenant improvements, and facility upgrades.

GFCI (Ground Fault Circuit Interrupter)

A ground fault circuit interrupter (GFCI) is a safety device that detects a ground fault — current taking an unintended path to ground, often through a person — and interrupts the circuit within milliseconds to prevent electrocution. GFCIs are required by the NEC in commercial kitchens, bathrooms, outdoor locations, and anywhere electrical equipment is used near water. They can be installed as outlets or as circuit breakers in the panel.

Grounding / Bonding

Grounding connects the electrical system to the earth to provide a safe path for fault current and to stabilize voltage levels. Bonding connects metallic components of an electrical system together so they are at the same electrical potential, preventing voltage differences that could cause shock. Both grounding and bonding are required by the NEC and are critical for the safe operation of commercial electrical systems.

Junction Box

A junction box is an enclosure that houses electrical wire connections and protects them from physical damage and environmental exposure. The NEC requires that all wire splices and connections be made inside a listed enclosure such as a junction box. Junction boxes must remain accessible for inspection and maintenance and cannot be permanently concealed behind finished walls or ceilings.

Low-Voltage Wiring

Low-voltage wiring refers to electrical systems that operate at 50 volts or less, including data networks, telephone systems, security systems, fire alarm systems, and audio-visual infrastructure. Low-voltage systems are governed by separate NEC articles and often require specialized licensing. In commercial facilities, low-voltage wiring is installed alongside power wiring but in separate conduit or cable pathways. FSG's technology services include low-voltage infrastructure installation for commercial facilities.

Wire Gauge (AWG)

Wire gauge refers to the physical size of an electrical conductor, expressed as an American Wire Gauge (AWG) number. Smaller AWG numbers indicate larger wire diameter and higher current-carrying capacity. For example, 12 AWG wire is rated for 20 amps, while 10 AWG wire is rated for 30 amps. Selecting the correct wire gauge is a code requirement and a safety necessity: undersized wire overheats, creating a fire hazard.

Codes, Safety & Compliance

AFCI (Arc Fault Circuit Interrupter)

See AFCI in the Wiring, Conduit & Components section above.

AHJ (Authority Having Jurisdiction)

The authority having jurisdiction (AHJ) is the organization, office, or individual responsible for enforcing the requirements of applicable codes and standards, and approving equipment, materials, installations, and procedures. In commercial electrical work, the AHJ is typically the local building department or fire marshal. The AHJ has final authority on code interpretation and inspection approval.

Arc Flash

An arc flash is an explosive release of energy caused by an electrical fault between two energized conductors or between a conductor and ground. Arc flashes can cause severe burns, blindness, hearing loss, and death. NFPA 70E establishes requirements for arc flash hazard analysis, labeling of electrical equipment, and the selection of personal protective equipment (PPE) for workers performing energized electrical work. FSG's safety and risk policies address arc flash and other electrical safety requirements.

Electrical Inspection

An electrical inspection is a review of installed electrical work by the authority having jurisdiction (AHJ) to verify compliance with applicable codes and standards. Inspections occur at multiple stages of a project: rough-in, service entrance, and final. Work that fails inspection must be corrected and reinspected before it can be energized or concealed. Licensed electrical contractors are required to schedule and pass inspections as part of any permitted project.

Electrical Permit

An electrical permit is an authorization issued by the local authority having jurisdiction that allows electrical work to proceed on a specific project. Permits are required for most new installations, service upgrades, panel replacements, and significant alterations to existing systems. Working without a required permit creates code compliance issues, insurance exposure, and potential safety hazards that can affect building sale or refinancing.

NEC (National Electrical Code)

The National Electrical Code (NEC), published by the National Fire Protection Association as NFPA 70, is the benchmark standard for safe electrical installation in the United States. It is adopted by most states and municipalities as the basis for their electrical codes, sometimes with local amendments. The NEC is updated every three years and governs everything from wire sizing and conduit fill to grounding requirements and equipment installation.

NEMA Rating

A NEMA rating is a classification system published by the National Electrical Manufacturers Association that defines the environmental protection level of electrical enclosures. NEMA ratings indicate whether an enclosure is suitable for use in dry, wet, dusty, corrosive, or hazardous environments. For example, NEMA 4 enclosures are watertight and suitable for outdoor use, while NEMA 4X adds corrosion resistance. Selecting the correct NEMA rating for panels, disconnects, and junction boxes in industrial or outdoor environments is a code and safety requirement.

OSHA Electrical Safety Standards

OSHA's electrical safety standards (29 CFR 1910 Subpart S for general industry, 29 CFR 1926 Subpart K for construction) establish requirements for safe electrical work practices, equipment guarding, lockout/tagout procedures, and personal protective equipment. These standards apply to any employer whose workers may be exposed to electrical hazards, including facilities teams and contractors performing electrical maintenance and installation work.

Short Circuit

A short circuit occurs when electrical current takes an unintended low-resistance path, resulting in a sudden and massive surge of current. Short circuits are caused by wiring failures, equipment faults, or physical damage to conductors. Circuit breakers and fuses are designed to interrupt the circuit during a short circuit to prevent fires, equipment damage, and electrocution. Persistent short circuits indicate a wiring problem that requires professional diagnosis and repair.

Thermal Imaging / Infrared Inspection

Thermal imaging uses an infrared camera to detect heat signatures in electrical panels, connections, and equipment. Overheating connections, overloaded breakers, and failing components produce heat before they fail visibly, making thermal imaging a powerful predictive maintenance tool. Many insurance carriers and property managers require periodic infrared inspections of electrical systems as a condition of coverage or due diligence. FSG's proactive maintenance services include thermal imaging inspections for commercial electrical systems.

Project & Contractor Terms

As-Built Drawings

As-built drawings are a set of construction documents revised to reflect the actual conditions of a completed installation, including any changes made during construction. As-builts document the precise location of conduit runs, panel schedules, circuit routing, and equipment placement. They are essential for future maintenance, renovation, and emergency response planning. Many facility operators require contractors to provide as-builts as a condition of project closeout.

BIM (Building Information Modeling)

Building Information Modeling (BIM) is a digital process that uses three-dimensional models to plan, coordinate, and document building systems before and during construction. In electrical work, BIM is used to coordinate conduit and equipment placement with other trades, identify conflicts before construction begins, and produce accurate installation documentation. FSG's approach to BIM and spatial coordination is covered in detail on our blog.

Change Order

A change order is a formal modification to the original scope of work, schedule, or contract price on a construction project. Change orders are issued when conditions differ from what was originally anticipated, when the owner requests additional work, or when unforeseen site conditions require a different approach. All change orders should be documented in writing and signed by both parties before the additional work begins.

Commissioning

Commissioning is the process of verifying that installed electrical systems and equipment are functioning correctly and in accordance with the design intent and project specifications. It includes testing, adjusting, and documenting system performance before final acceptance. For complex systems such as generator and transfer switch installations, motor control centers, and building automation integration, commissioning is a critical step that ensures reliable operation from day one.

Electrical Contractor vs. Electrician

An electrician is a licensed tradesperson who installs, maintains, and repairs electrical systems. An electrical contractor is a licensed business entity that employs electricians and holds the contractor license required to pull permits and enter into contracts for electrical work. When hiring for a commercial project, you are contracting with the electrical contractor, not directly with individual electricians. FSG is one of the largest electrical contractors in the United States, operating across more than 30 locations nationwide.

Load Calculation

A load calculation is an engineering analysis that determines the total electrical demand of a facility or portion of a facility, based on the connected equipment, lighting, HVAC, and other loads. Load calculations are required by the NEC for service sizing, panel sizing, and feeder design. They are the foundation for any service upgrade or capacity expansion project and are typically performed before a project is bid or permitted.

Punch List

A punch list is a document prepared near the end of a construction project that identifies items that have not been completed, do not meet specifications, or require correction before the project can be formally closed out. In electrical projects, punch list items commonly include missing cover plates, unlabeled circuits, incomplete conduit sealing, and equipment that has not been tested or commissioned. Resolving the punch list is a condition of final payment in most contracts.

RFI (Request for Information)

An RFI is a formal written request from a contractor to the design team, owner, or another party asking for clarification on plans, specifications, or existing conditions. In electrical projects, RFIs are commonly used to resolve conflicts between electrical drawings and field conditions, clarify equipment specifications, or address gaps in the project documents. RFIs create a documented record of how ambiguities were resolved, which is important for change order management and dispute resolution.

Scope of Work

The scope of work is a detailed description of the work to be performed on a project, including what is included and what is explicitly excluded. A well-defined scope of work is the foundation of a reliable electrical project estimate and contract. Vague or incomplete scopes are the most common source of cost overruns, disputes, and unmet expectations on commercial electrical projects.

Submittals

Submittals are documents provided by the contractor to the design team for review and approval before materials or equipment are ordered or installed. In electrical projects, submittals typically include product data sheets, shop drawings, equipment schedules, and engineering calculations. The submittal process ensures that proposed materials and equipment meet the project specifications before they arrive on the job site. FSG's electrical construction process includes a structured submittal workflow to keep projects on schedule.