North Carolina Low Voltage Practice key terms

A circuit supplied by a listed Class 2 power source and limited in voltage and power so it presents a low fire and shock hazard, allowing less restrictive wiring methods.

A circuit supplied by a listed Class 3 power source that is voltage-limited but carries higher current than Class 2, requiring wiring methods closer to those for power circuits.

A circuit whose energy is capped by a listed power source or overcurrent protection in accordance with its article, reducing fire and shock risk and permitting reduced wiring requirements.

A plenum-rated Class 3 cable whose jacket and insulation pass the NFPA 262 Steiner tunnel test, permitting installation in ducts and plenums without conduit.

Communications plenum cable tested to NFPA 262, used in air-handling spaces; the "P" suffix marks plenum rating for Articles 800 and 820 cables.

A cable such as CMR or CL3R tested to UL 1666 for flame propagation in vertical shafts, suitable for risers but not for plenums.

An air-handling space used for supply, return, or exhaust air, such as a dropped ceiling or raised floor, where only plenum-rated wiring and materials are permitted.

A vertical shaft or penetration connecting floors of a building through which cables run between levels; cable flame ratings for risers are governed by UL 1666.

A listed material or assembly installed to seal a penetration through a fire-rated wall, floor, or membrane so the fire rating of the barrier is maintained.

A short section of conduit or tubing through a wall or floor that carries cable and protects it from abrasion; a sleeve does not by itself satisfy firestopping requirements.

The percentage of a raceway's internal cross-sectional area occupied by conductors and cables, limited by NEC Chapter 9 tables to allow pulling and heat dissipation.

A hook-shaped hanger used to support bundles of low-voltage cable at intervals specified by the manufacturer and the applicable article, controlling sag and strain.

A rigid metal or nonmetallic raceway system with open top used to support and route cables; fill, support, and grounding requirements apply under NEC Article 392.

Installed cable that is not terminated at equipment and not identified for future use, which Articles 725, 760, 770, 800, and 820 require to be removed or tagged.

The relationship stating that voltage equals current multiplied by resistance (E = I × R), used to size conductors and predict voltage drop in low-voltage circuits.

The relationship that electrical power equals voltage multiplied by current (P = E × I), used to compute load, source capacity, and heat in low-voltage systems.

The loss of voltage along a conductor caused by its resistance, calculated as 2 × I × R for a two-wire circuit and critical for long low-voltage runs.

American Wire Gauge, the standard numbering system for conductor size in which lower numbers indicate larger conductors and lower resistance per unit length.

A circuit in which current has one path, so the same current flows through every component and the total resistance equals the sum of individual resistances.

A circuit in which components connect across the same two nodes, so voltage is common to all branches and total current is the sum of branch currents.

A fire alarm circuit that monitors the integrity of wiring and devices, such as initiating device circuits and notification appliance circuits, and signals abnormal conditions.

The fire alarm circuit connecting detectors and manual pull stations to the control unit, transmitting alarm signals when a device operates.

The fire alarm circuit that powers horns, strobes, and speakers, delivering the audible and visible signals required by the adopted building and fire codes.

A fire alarm architecture in which each device has a unique address, letting the panel report the specific device in alarm or trouble rather than only a zone.

A fire alarm signaling circuit that continues to operate when a single open or ground fault occurs, because the conductors leave and return to the panel.

A fire alarm signaling circuit that cannot operate past a single open fault; the panel must then indicate a trouble condition.

An emergency communications system using speakers and intelligible voice messages to direct occupants, often combined with fire alarm notification.

The conductor that bonds non-current-carrying metal parts of equipment to the system grounding point, providing a low-impedance path for fault current.

A conductor that ensures electrical continuity between metal parts, such as raceways, boxes, and panels, so they remain at the same potential.

A conductive object such as a ground rod, plate, or building steel that establishes a direct connection to earth for the grounding system.

A device that trips when it detects a small current imbalance between the ungrounded and grounded conductors, protecting people from shock.

A twisted-pair cable rated by performance category, such as Cat 5e, Cat 6, or Cat 6A, specifying bandwidth and crosstalk characteristics for data networks.

Two insulated conductors twisted together so that noise couples equally to both, allowing the receiver to reject common-mode interference.

Unwanted signal coupling from one pair or cable to another, measured as near-end or far-end crosstalk and controlled by twist rates and installation practice.

The installed portion of a cabling run from the work area outlet to the patch panel, excluding patch cords, and the basis for field certification testing.

A cable that carries data as light through a glass or plastic core, offering high bandwidth and immunity to electromagnetic interference over long distances.

Optical fiber nonconductive plenum cable, rated for air-handling spaces under NEC Article 770 because it has no metallic members and passes NFPA 262.

The North Carolina specialty license that authorizes a qualified individual to contract for low voltage wiring work within the scope defined by state statute and board rules.

The person who has passed the licensing examination and is designated as the license holder responsible for the electrical contracting work of a firm.

Written authorization from the local code enforcement jurisdiction to begin work, required before installation and closed out by inspection.

A document, sometimes required by rule, that the installer provides to the owner or authority confirming work was performed and tested as specified.

A safety procedure that isolates hazardous energy, applies a lock and tag, and verifies de-energization before work begins on equipment.

Wearable gear such as safety glasses, gloves, hard hats, and arc-rated clothing selected to reduce injury from workplace hazards.

A space large enough to enter, with limited entry and exit, not designed for continuous occupancy, requiring evaluation and often a permit before entry.