DC Electrician key terms

The relationship stating that voltage equals current multiplied by resistance (E = I × R). Electricians use it to calculate an unknown value when the other two are known in a circuit.

The loss of voltage along conductors caused by their resistance as current flows. Excessive drop at the load can cause equipment malfunction, so feeders and branch circuits are sized and limited by code.

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

The ratio of real power to apparent power in an alternating-current circuit, ranging from zero to one. Low power factor means more current for the same useful work and affects conductor and equipment sizing.

The ratio of the maximum demand on a system to the total connected load it serves. Applying it lets electricians size service and feeder equipment realistically rather than by summing every load at full value.

The structured method of totaling general lighting, receptacle, appliance, motor, and heating loads to determine service and feeder capacity. It applies demand factors and code-specified minimum unit loads to each category.

An unintentional connection between an energized conductor and ground or grounded equipment. It creates stray current that can shock people, start fires, or trip protective devices.

An accidental low-resistance connection between two energized conductors of different potential. Very high current flows, so overcurrent devices must interrupt it quickly to prevent damage.

A breaker or fuse designed to open a circuit automatically when current exceeds a safe level. It protects conductors and equipment from overheating caused by overloads and short circuits.

The maximum fault current a protective device can safely interrupt without being damaged. It must equal or exceed the available fault current at the point of installation.

A device that senses small current imbalances between the ungrounded and grounded conductors and trips quickly to prevent shock. It is required in bathrooms, kitchens, outdoors, and other wet or high-risk locations.

A device that detects the signature of dangerous arcing in wiring and opens the circuit. It protects against fires caused by damaged cords, loose connections, and insulation breakdown.

The conductor that connects metal enclosures and equipment frames to the grounding system. It provides a low-impedance fault path so protective devices operate during a ground fault.

The permanent joining of metal parts to form an electrically conductive path that ensures electrical continuity. It equalizes potential so that metal surfaces cannot deliver a dangerous shock.

A conductive object, such as a ground rod or metal water pipe, that establishes a direct connection to the earth. It anchors the electrical system's reference to ground potential.

The conductor that connects the grounding electrode to the system's grounded conductor or equipment grounding terminal. It carries fault and lightning current to earth.

The conductors that carry power from the utility service point to the service equipment inside a building. They are sized from load calculations and protected by the service disconnect.

An enclosure containing buses, breakers, and terminals that distributes power to branch circuits from a single supply. It must be accessible, labeled, and installed with adequate working clearance.

The required clear floor space in front of electrical equipment that keeps workers safe while servicing it. Depth depends on voltage and whether live parts are exposed on one or both sides.

A safety procedure that isolates energy sources and applies locks and warning tags before work begins. It prevents accidental energization of equipment being serviced or maintained.

Clothing and gear such as insulated gloves, arc-rated clothing, and eye protection worn to reduce injury from shock, arc flash, and burns. Selection depends on a documented hazard assessment.

A sudden release of energy caused by an electrical arc through air, producing intense heat, light, and pressure. It can ignite clothing and cause severe burns, so boundaries and protective equipment are required.

The percentage of a raceway's cross-sectional area occupied by conductors. Code limits fill so conductors can be pulled without damage and heat can dissipate properly.

An enclosed channel, such as conduit or tubing, that holds and routes conductors. It provides physical protection and, for metal types, a possible equipment grounding path.

The calculation that limits how many conductors and devices may be installed in an outlet or junction box. It accounts for conductor size, fittings, and grounding conductors to prevent crowding and overheating.

The adjustment of a conductor's current rating for high ambient temperature and for more than three current-carrying conductors in a raceway. These conditions reduce heat dissipation and require derating.

A factory assembly of insulated conductors enclosed in a flexible outer jacket, commonly used for residential branch circuits. It must be protected where subject to physical damage and secured per code intervals.

The required securing and stapling of cable at specified intervals and near boxes so it stays in place. Proper support prevents strain on terminations and damage to the cable jacket.

A contact device installed at an outlet for connecting a plug to the branch circuit. Its rating, grounding type, and location must match the circuit and code requirements.

The conductor that runs from a switch to the controlled load, carrying switched power rather than constant power. It is often re-identified at the panel to distinguish it from unswitched conductors.

A switch with three terminals that, paired with another three-way switch, allows a load to be controlled from two locations. Traveler conductors connect the two switches.

A device that protects a motor from sustained excess current that would overheat the windings. It is separate from branch-circuit short-circuit protection and is sized to the motor's service factor.

A device that changes alternating-current voltage through magnetic coupling between windings. It steps voltage up or down, and its kVA rating and connections affect available fault current and system design.

The formal approval process in which a licensed electrician obtains a permit before work and an authority inspects it afterward. It verifies code compliance and is required for most installations and alterations.

The education, experience, examination, and continuing-education conditions a jurisdiction sets before a person may perform electrical work for pay. Working outside a license scope can bring fines and license discipline.

The rules governing enforceable agreements, including offer, acceptance, consideration, and breach remedies. Electricians rely on clear written contracts to define scope, price, schedule, and change orders.

A legal claim that lets unpaid contractors and suppliers place an encumbrance on improved property to secure payment. Strict notice and filing deadlines apply, so records and prompt action matter.