New Mexico Low Voltage Practice key terms

The relationship stating that voltage equals current multiplied by resistance (E = I × R); knowing any two values lets you calculate the third in a DC circuit.

The equation P = E × I for DC circuits, giving wattage from voltage and current; in AC circuits it must be adjusted by the power factor for true power.

The ratio of true power to apparent power in an AC circuit, expressed from 0 to 1; low values mean more current is drawn for the same useful work.

The loss of voltage along conductors caused by their resistance, reducing voltage at the load; long low-voltage runs make this a critical design concern.

A unit of conductor cross-sectional area based on the square of the diameter in thousandths of an inch; used in voltage-drop and ampacity calculations.

The maximum current a conductor can carry continuously under stated conditions without exceeding its temperature rating; determined from tables and corrected for ambient temperature and conduit fill.

Reducing a conductor's allowable ampacity to account for conditions such as high ambient temperature or many current-carrying conductors bundled in one raceway.

A circuit with a single current path where the same current flows through every component and the total resistance is the sum of individual resistances.

A circuit with multiple current paths across the same voltage, where total current is the sum of branch currents and total resistance is less than any single branch.

A circuit supplied by a listed power source limited in voltage and energy so it presents low fire and shock hazard, allowing less restrictive wiring methods for control and signal loads.

A circuit with voltage and power limits higher than Class 2 but still controlled, permitting lighter wiring methods than line-voltage branch circuits while requiring some separation from power conductors.

A circuit whose source is listed and limits available current and voltage, typically used for fire alarm, security, and communication equipment so standard wiring methods may be relaxed.

Non-power-limited fire alarm circuit; a fire alarm circuit not limited in power, requiring line-voltage wiring methods and separation from power-limited circuits.

Power-limited fire alarm circuit; a fire alarm circuit supplied by a listed limited-power source, allowing reduced wiring requirements under the fire alarm article.

The unit of apparent power in an AC circuit, equal to RMS voltage multiplied by RMS current without regard to phase angle between them.

The set of electrodes and bonding jumpers that connects an electrical system to earth, establishing a reference potential and providing a path for lightning and fault currents.

The conductor that connects the metal enclosure of equipment to the grounding system, providing a low-impedance path for fault current so overcurrent devices open.

The permanent joining of metal parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct fault current safely.

An enclosed channel of metal or nonmetallic material designed to hold and protect conductors, such as conduit, tubing, or wireway.

Electrical metallic tubing; a thin-wall steel or aluminum raceway joined with couplings and connectors, widely used indoors for exposed and concealed low-voltage feeder runs.

The percentage of a raceway's internal cross section occupied by conductors; limits prevent overheating and make pulling conductors practical.

A space used for air handling in a building, such as above a suspended ceiling; cable installed there must be listed for plenum use with low smoke and flame characteristics.

A vertical shaft or run between floors; cables installed in it generally must carry a riser rating unless enclosed in a raceway or otherwise protected.

The listing designation (such as CMP, CMR, CM, or CMX) indicating where a communications cable may be installed based on its flame and smoke performance.

The required internal volume of an outlet, device, or junction box based on the number and size of conductors, devices, and fittings it contains.

A breaker or fuse that opens a circuit when current exceeds its rating, protecting conductors and equipment from overheating and fault damage.

The required clear space in front of electrical equipment that allows a person to work safely and escape a hazard without obstruction.

A procedure for de-energizing equipment, applying a lock and tag, and verifying absence of voltage before work begins so energy cannot be unexpectedly restored.

A dangerous release of energy caused by an electrical fault through air, producing intense heat, light, and pressure; requires appropriate personal protective equipment and safe work practices.

Personal protective equipment such as insulated gloves, arc-rated clothing, and eye protection worn to reduce injury from shock, arc flash, and physical hazards.

A test instrument that measures voltage, resistance, and often current; selecting the correct function and range before contact with a circuit is essential for safety and accuracy.

A device that confirms an unbroken conductive path by signaling when resistance is very low; used on de-energized conductors to verify connections and identify opens.

A pair of tools used to trace and identify a specific cable among many by injecting a signal on one end and locating it with a receiver at the other.

An official authorization from the local building or electrical authority to perform specified work, typically required before installation and followed by inspections.

A legally binding agreement defining scope, price, schedule, and responsibilities between a contractor and client; changes should be documented in writing.

A written amendment to a contract that adjusts scope, price, or schedule; without one, extra work may go uncompensated.

A legal claim against property securing payment for labor or materials supplied; contractors and suppliers may file one when unpaid.

A review of installed work by the authority having jurisdiction to confirm compliance with adopted codes before the work is covered or energized.

Authority having jurisdiction; the organization or individual responsible for approving equipment, installations, and enforcing the adopted code in a given area.

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

A fire alarm arrangement where devices share a zone circuit, so the panel reports the zone rather than the individual device that activated.

A component such as a smoke detector, pull station, or waterflow switch that signals the fire alarm control unit when a fire condition is detected.

A device such as a horn, strobe, or speaker that alerts occupants of a fire alarm condition using audible or visible signals.

A transformer device that converts between balanced and unbalanced signals, commonly used to carry video or data over twisted-pair cable.

A standardized layout of data cabling using defined subsystems, connectors, and distances so voice, data, and video services can be reliably installed and changed.