MT Journeyman Electrician key terms

The maximum current, in amperes, a conductor can carry continuously under stated conditions without exceeding its temperature rating. It depends on conductor material, size, insulation type, and ambient temperature.

The loss of voltage along a circuit caused by conductor resistance and reactance. Excessive drop reduces equipment performance; the NEC recommends keeping total drop within about 3 percent for branch circuits and 5 percent overall.

The relationship stating voltage equals current times resistance (E = I × R). It is the basis for calculating load current, conductor sizing, and protective device ratings in practical field work.

The ratio of real power in watts to apparent power in volt-amperes in an AC circuit, ranging from 0 to 1. Low power factor increases current for a given load and affects conductor and service sizing.

A condition in a multiwire or three-phase system where connected loads draw roughly equal current on each ungrounded conductor. Balancing reduces neutral current, voltage drop, and overheating.

An adjustment applied to conductor ampacity when the surrounding air or soil temperature differs from the table's baseline. Higher temperatures reduce allowable current, so correction factors are applied from the appropriate NEC table.

The reduction of allowable ampacity when more than three current-carrying conductors share a raceway or cable. The adjustment accounts for mutual heating and is applied after ambient temperature correction.

A thermoplastic-insulated conductor rated for dry locations at higher temperature and, in the dual-rated version, for wet locations at a lower temperature. It is the most common building wire in commercial work.

Metal-clad cable containing insulated conductors in a flexible metallic armor, with or without a grounding conductor. It is permitted in many commercial applications where flexibility and physical protection are needed.

The percentage of a raceway's internal cross-sectional area occupied by conductors. Limits vary by conductor count and type, and compliance is checked with the NEC's chapter 9 tables.

An enclosure installed in a raceway run to allow conductors to be pulled and spliced. Minimum dimensions depend on raceway size and whether the run is straight or contains bends.

The required internal volume of an outlet, device, or junction box based on the number and size of conductors, devices, clamps, and grounding conductors. Insufficient volume causes overheating and code violations.

The conductor that connects the non-current-carrying metal parts of equipment to the grounding system, providing a low-impedance path for fault current. It is sized by the rating of the overcurrent device protecting the circuit.

A conductor that ensures electrical continuity between metal parts that must be electrically connected. It is sized according to the circuit conductors or the equipment grounding conductor, depending on its function.

A conductive object in direct contact with the earth, such as a ground rod, metal water pipe, or concrete-encased electrode, that establishes the system's reference to earth potential.

An unintentional electrical connection between an ungrounded conductor and ground or grounded metal. It is cleared by the equipment grounding path and the overcurrent device or a ground-fault protective device.

A fuse or circuit breaker that opens a circuit when current exceeds a set value for a set time. It protects conductors and equipment from overloads and short circuits.

A device that interrupts a circuit when it detects a small current imbalance between the ungrounded and grounded conductors, indicating current is leaking to ground. It protects people from shock.

A device that detects and interrupts dangerous arcing in a circuit, such as from damaged insulation or loose connections. AFCI protection is required for many dwelling-unit branch circuits.

A branch circuit with two or more ungrounded conductors sharing a neutral, having a voltage between them and the neutral. It requires simultaneous disconnect of all ungrounded conductors and careful neutral handling.

A 20-ampere branch circuit serving receptacle outlets in a dwelling kitchen, pantry, or dining area. At least two are required, and the load is included in the service calculation at a demand factor.

All circuit conductors between the service equipment or source of a separately derived system and the final branch-circuit overcurrent device. Feeders carry the combined load of the branch circuits they supply.

The conductors from the service point to the service disconnecting means. They are sized for the calculated load using the standard or optional method and are protected by the service overcurrent device.

A ratio applied to a total connected load to account for the fact that not all loads operate at once. It reduces calculated feeder and service size while maintaining safe capacity.

A load that operates at maximum current for three hours or more. Its calculated value must be increased by 25 percent when sizing branch-circuit conductors and overcurrent devices.

The current a motor draws at rated load, speed, and voltage, taken from NEC tables rather than the motor nameplate. It is used to size branch-circuit conductors, overload protection, and disconnects.

A device, such as a thermal overload relay, that protects the motor from sustained overcurrent due to overload. It is sized from the motor nameplate current and is separate from short-circuit protection.

A means to disconnect the motor and controller from the power source, located within sight of the motor or capable of being locked open. It must be rated for the motor's horsepower and voltage.

A classification of how long a motor or controller is expected to operate, such as continuous, intermittent, or periodic. It affects conductor and protective device sizing and equipment selection.

An area where fire or explosion hazards may exist due to flammable gases, vapors, dusts, or fibers. Equipment and wiring methods must be specially approved for the specific class, division, or zone.

Enclosures and devices designed to contain an internal explosion and prevent ignition of surrounding flammable atmospheres. They are required only in specific classified locations and must be installed per listing.

An installation location subject to saturation with water or other liquids, such as outdoors or in wash-down areas. It requires weatherproof or watertight equipment and wiring methods rated for wet use.

Acceptable to the authority having jurisdiction. The term does not necessarily mean listed or labeled; acceptance may be based on field evaluation or other evidence of suitability.

The organization, office, or individual responsible for enforcing the code and approving equipment, materials, and installations. In Montana, local building officials and the state electrical board share enforcement roles.

A credential issued by the State of Montana allowing a person to perform electrical work under the scope defined by statute and rule. It requires documented experience, examination, and continuing education for renewal.

Required coursework that licensed electricians complete during each renewal cycle to maintain their license. Montana rules specify the number of hours and acceptable subject areas, including code updates and safety.

The distance from energized equipment within which a person could receive a second-degree burn from an arc flash. It is calculated from incident energy and determines required personal protective equipment.

The amount of thermal energy reaching a surface at a given distance during an arc flash, usually expressed in calories per square centimeter. It is used to select PPE and set approach boundaries.

Clothing and gear such as arc-rated shirts, pants, face shields, and gloves worn to protect a worker from electrical and thermal hazards. Selection is based on the hazard assessment and incident energy.

A formal document authorizing work on or near energized equipment after justifying that de-energizing is infeasible. It records the hazard assessment, boundaries, PPE, and qualified persons involved.

A procedure for isolating energy sources and applying locks and tags so equipment cannot be re-energized during work. It is a core requirement of electrical safe work practices and OSHA rules.