MA Electrician key terms

The maximum current, in amperes, that a conductor can carry continuously under its conditions of use without exceeding its temperature rating. It depends on conductor size, insulation, ambient temperature, and the number of current-carrying conductors bundled together.

An enclosed channel of metal or nonmetallic material designed expressly for holding wires, cables, or busbars. Raceways provide physical protection and a controlled path for conductors between boxes and equipment.

The percentage of a raceway's internal cross-sectional area occupied by conductors. The code limits fill, generally to 40 percent for three or more conductors, so wires can be pulled without damage and heat can dissipate.

The required cubic-inch volume of an outlet, device, or junction box, calculated from the number and size of conductors, devices, fittings, and grounds it contains, so wires are not overcrowded or damaged.

A factory assembly of two or more insulated conductors enclosed in a moisture-resistant, flame-retardant jacket, used mainly in dry interior locations such as wood-frame dwellings.

The circuit conductors between the final overcurrent device protecting the circuit and the outlet or outlets it serves, such as receptacles, luminaires, or appliances.

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

The conductors between the service point, typically the utility connection, and the service equipment disconnecting means, carrying the total supply current for the premises.

The ratio of the maximum demand on a system, or part of it, to the total connected load. It lets feeders and services be sized for realistic peak use rather than every load at once.

A load whose maximum current is expected to continue for three hours or more. Its rating is multiplied by 125 percent when sizing conductors and overcurrent devices for the circuit.

A circuit breaker or receptacle device that recognizes characteristic arcing-fault current and voltage patterns in branch-circuit wiring and opens the circuit to reduce fire risk.

Any current greater than the rated current of equipment or the ampacity of a conductor. It can come from overload, short circuit, or ground fault and must be cleared by a protective device.

A device that compares current leaving and returning on a circuit and trips quickly when a small imbalance shows current is leaking to ground, protecting people from shock.

The conductor connecting the exposed, normally non-current-carrying metal parts of equipment to the system grounding point. It provides a low-impedance fault path so overcurrent devices open.

The conductor that connects the system grounded conductor, service equipment, or equipment grounding conductors to the grounding electrode, such as a rod, plate, or metal water pipe.

The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and can safely carry any current likely to be imposed.

A circuit conductor intentionally connected to earth at the source, commonly called the neutral, that carries return current for line-to-neutral loads and is finished in white or gray.

The reduction in voltage along circuit conductors caused by their resistance and the current flowing through them. Excessive drop causes dim lights and poor motor performance.

The relationship stating that voltage equals current multiplied by resistance. Electricians use it to find current, voltage, or resistance and to predict voltage drop and fault current.

The ratio of real power in watts to apparent power in volt-amperes in an alternating-current circuit. A low value means more current is drawn to deliver the same useful work.

The current a motor draws at rated voltage when its rotor is not turning, sometimes called starting current. It is used for sizing disconnecting means and short-circuit protective devices.

A device such as a thermal relay that protects a motor from overheating caused by running above its rating for too long. It is separate from branch-circuit short-circuit and ground-fault protection.

A switch or circuit breaker that isolates a motor and its controller from the supply for servicing, sized at not less than 115 percent of the motor's rated full-load current.

An area where flammable gases, vapors, liquids, combustible dusts, or ignitible fibers may be present in quantities that require special equipment and wiring to prevent ignition.

A location where ignitable concentrations of flammable gases or vapors exist under normal operating conditions, or may exist often through repair or maintenance, requiring the most restrictive wiring methods.

A circuit or equipment design in which electrical energy is limited so that sparks or heat cannot ignite a specific hazardous atmosphere under normal operation or specified fault conditions.

The Massachusetts regulation that adopts the National Electrical Code with state amendments, making it the enforceable electrical installation code throughout the Commonwealth.

The Massachusetts board that licenses electricians, approves education and examination programs, and administers the statutes and regulations governing electrical practice in the Commonwealth.

An official authorization from the local wiring inspector that allows electrical work to begin, subject to inspection and compliance with the code and local rules.

The organization, office, or individual responsible for enforcing code requirements, approving equipment and materials, and issuing permits and inspections for electrical work.

Acceptable to the authority having jurisdiction. Approval may be based on inspection, testing, or listing that shows equipment or a method is suitable for its intended use.

Equipment or materials included in a published list by a nationally recognized testing laboratory that maintains periodic inspection and finds the product suitable for a stated purpose.

A rapid release of energy from an electric arc that produces intense heat, light, sound, and pressure, capable of severely burning or injuring workers and damaging equipment.

A procedure that isolates energy sources, applies locks and tags, and verifies de-energization so equipment cannot be restarted while a worker is servicing it.

Clothing and equipment tested to withstand a stated level of incident energy from an arc flash, selected according to the calculated or tabulated hazard for the task.

The clear area in front of electrical equipment that must be kept free of obstructions so qualified persons can safely operate, inspect, and maintain the equipment.