Glossary of electrical terms

The “classic” breaker in the consumer unit. It automatically interrupts the circuit on overload (via a thermal element) and on short circuit (via a magnetic element). It protects the cable and the equipment, but it does NOT protect a person against electric shock.

The “residual current device”. It compares the current entering with the current leaving the circuit; if a leakage to earth appears (for example through a person’s body), it trips within a few tenths of a second. The usual sensitivity for personal protection is 30 mA. It does NOT protect against overload or short circuit.

I7-2011, Art. 4.1.5.2.7 classifies RCDs by time delay: undelayed, general use, with tripping times of 40…300 ms; with a time delay of type “S” for selectivity, with times of 150…500 ms.

Two in one: it combines the function of an RCCB (residual current protection against leakage) with that of an MCB (overload and short-circuit protection) in a single device. It takes up less space on the rail and protects a single complete circuit.

It senses dangerous electric arcs (loose contacts, damaged insulation, crushed conductors) that can cause fires but which an MCB or an RCD does not “feel”. It interrupts the circuit when it detects such an arc.

The 2023 Amendments to I7 define: AFDD — arc fault detection device, intended to limit the effects of arc faults by disconnecting the circuit when an arc fault is detected; and an “arc fault” = an unintended and dangerous series or parallel electric arc between conductors.

The “surge arrester”. It limits the voltage peaks that appear from lightning or network switching, diverting the surplus to earth. It protects sensitive equipment (electronics, appliances) against transient overvoltages.

A more robust variant of the circuit breaker, for high currents (tens to hundreds of amperes). It has adjustable tripping thresholds and a higher breaking capacity. In residential work it usually appears as the main switch-disconnector on larger boards.

Indicates at what multiple of the rated current the magnetic part of an MCB trips “instantaneously”. B = 3–5×In (resistive circuits, lamps, sockets), C = 5–10×In (general use, small motors), D = 10–20×In (loads with a high inrush peak).

Per IEC 60898-1, the instantaneous tripping bands are: B = 3–5×In, C = 5–10×In, D = 10–20×In.

The coordination of series-connected protective devices so that, on a fault, only the device closest to the fault trips — isolating only the affected part, without taking out the whole board. In practice: the “main switch” does not trip for a short circuit on a single circuit.

I7-2011, Art. 4.3.7.1: when several protective devices are connected in series, their characteristics are chosen so that selectivity is ensured; on a fault the protective device closest to it must operate, isolating only that section, without taking the whole installation out of service.

An earthing system in which the neutral conductor (N) and the protective conductor (PE) are separate along the entire route, from source to load. It is the preferred system in modern residential installations, as it allows RCDs to be used throughout.

A system in which the neutral and protective functions are combined in a single conductor (PEN) along the entire route. It does not allow the use of RCDs and is no longer recommended for new circuits in indoor installations.

A mixed system: a combined PEN conductor on the distribution side (up to near the building), then separated into N and PE inside. Very common in Romanian residential service connections. The point of separation is connected to the earth electrode.

A system in which the neutral point of the source is earthed, while the exposed-conductive-parts of the load have their own independent earth electrode. It mandatorily requires RCD protection, because the fault-loop impedance is usually too high for an MCB.

A system in which the source is not earthed (or is earthed through a high impedance), while the exposed-conductive-parts are earthed. It allows continued operation on the first insulation fault and is used where continuity of supply is critical — rare in residential work.

A conductor that simultaneously serves as neutral (N) and protective (PE). It appears in TN-C systems and on the “C” part of TN-C-S. Coloured green-and-yellow with blue marking at the ends. It is never interrupted and no RCD is connected across it.

The green-and-yellow conductor that connects the metal exposed-conductive-parts of equipment to earth. On an insulation fault it gives the fault current a path to earth, allowing the protective device to trip and keeping the parts at a safe potential. It carries no current in normal operation.

The conductor (coloured blue) through which the working current returns in a single-phase circuit and which, in three-phase, takes the imbalance between phases. It is a live conductor — unlike PE, current flows through it in normal operation.

A two-digit code showing how well an enclosure is protected: the first digit — against the ingress of solid bodies and dust (0–6), the second — against water (0–8). E.g.: IP44 for covered outdoor use, IP65 for full dust protection + water jets.

The current actually drawn by the load supplied through the circuit, in normal operation. It is the starting point of sizing: the protective device and the cable are chosen based on how much current the load “draws”.

The setting value of the breaker/fuse (e.g. 10, 16, 20, 25 A). It must be chosen so that it is at least equal to the design current Ib and at most equal to the cable’s current-carrying capacity Iz: Ib ≤ In ≤ Iz.

The maximum current a cable can carry continuously without overheating, under real installation conditions (method of installation, grouping, temperature). The upper limit for choosing the protective device: In must not exceed Iz.

How large the current can be at a short circuit at a given point in the installation. It depends on the source and the network impedance up to that point. It is used to choose the breaking capacity of the protective devices.

I7-2011, Art. 3.1.4.1: the value of the prospective short-circuit current at the origin of the installations, taken into account when selecting the equipment, must be determined per NTE 006/06/00.

The greatest short-circuit current a breaker can safely interrupt without being destroyed. It must be at least equal to the prospective short-circuit current (Icc) at the point of installation.

I7-2011, Art. 4.3.5.1: the breaking capacity must be at least equal to the prospective short-circuit current at the place of installation; a lower value is allowed only if an upstream device has the required capacity and the characteristics are coordinated.

The decrease in voltage along the length of the cable, due to the conductor’s resistance and the current flowing through it. If it is too large, the equipment at the far end receives a voltage below the nominal one and works poorly. It is reduced by increasing the cable cross-sectional area or shortening the route.

I7-2011 requires checking the voltage drop (ch. 8, verifications) by measurement or by calculation; the practical limit values are expressed as percentages of the nominal voltage.

The sum of the rated powers of all the loads in an installation, assuming they would all run at once. It is a “catalogue” value — in reality they never all run simultaneously, which is why it is corrected by the diversity factor.

A sub-unity coefficient (e.g. 0.6–0.8 in a dwelling) that accounts for the fact that not all loads run at the same time. Connected load × diversity factor = the actual maximum demand, on the basis of which the distribution circuit and the service connection are sized.

Shows how much of the absorbed power is effectively converted into useful work (active power) compared with the total (apparent) power. For resistive loads (lamps, heating elements) it is ≈ 1; for motors and ballasts it is lower. A low cos φ means a higher current for the same useful power.

An electrically operated switch: a coil pulls in the contacts and connects/disconnects a load remotely, by a command (button, automation, relay). Used for frequently switched or high-power loads — water heaters, pumps, group lighting.

A device that switches a circuit depending on a condition: a control relay opens/closes on a weak signal, while a protection relay (thermal, voltage, time) acts when a quantity exceeds a threshold. It differs from a contactor in the lower currents on its contacts.

The part that connects two or more conductors mechanically and electrically, ensuring a tight, removable contact. DIN rail terminal blocks organise the connections in the board; a loose contact at a terminal is a frequent cause of overheating and arc faults.

A flush or surface-mounted box in which the joints between conductors are made and protected (branches to sockets, switches, luminaires). It must remain accessible, and the connections inside it must be made with terminals, not by simple twisting.

electricity supply from an electrical energy source (transformer, generator) provided to ensure the operation of a consumer’s electrical loads under normal conditions. This is usually the public distribution network.

supply provided to maintain, for purposes other than safety, the operation of an electrical installation or of parts of it in the event of an interruption of the normal supply (UPS, generator).

supply provided to keep in operation the electrical equipment and installations that are important for: • the health and safety of persons and domestic animals and/or • avoiding damage to the environment and to other equipment, where this is required by national regulations. It may be a UPS, generator, battery bank, etc.

electrical equipment intended to be connected to an electrical circuit in order to provide one or more of the following functions: protection, control, isolation, connection.

burn of the skin or of an organ, caused by the passage of electric current along the surface or through the depth of the body.

direct contact of persons or animals with live parts.

electrical contact of persons or animals with exposed-conductive-parts that have become live as a result of a fault.

element ensuring protection against direct contact from all usual directions of access.

part ensuring protection against direct contact in all usual directions of access.

metallic collector bar forming part of an equipotential network and ensuring the electrical connection of a number of electrical conductors for equipotential bonding purposes.

terminal provided on an equipment or device intended to be connected to an equipotential bonding system.

terminal or bar that forms part of the earthing arrangement of an installation and ensures the electrical connection of a number of conductors for earthing purposes.

laying element situated on or in the ground or in the floor, ventilated or closed, with dimensions that do not allow persons to walk through it, but in which conductors and cables are accessible throughout their length, during and after installation.

assembly of electrical equipment of an electrical installation protected by the same protective device.

electrical circuit provided for use as part of an electrical supply system for safety services.

electrical circuit intended to directly supply the load (utilization equipment) or socket-outlets.

electrical circuit supplying one or more distribution boards.

action intended to ensure the switching on, switching off, or changing of the electricity supply to an electrical installation or to a part of it for normal operation.

conductive part intended to carry a specified electric current.

protective conductor provided for making a protective equipotential bonding connection.

conductor providing a conductive path, or part of a conductive path, between a given point of a network, of an installation or of equipment and an earth electrode or an earth electrode network.

protective conductor provided for making a protective earthing connection.

conductor that is live in normal operation and able to take part in the transmission or distribution of electrical energy, but which is neither a neutral conductor nor a mid-point conductor.

conductor electrically connected to the neutral point of the source and able to contribute to the distribution of electrical energy.

conductor providing both the functions of a protective conductor and of a neutral conductor.

conductor providing both the functions of a protective conductor and of a mid-point conductor.

conductor providing both the functions of a protective conductor and of a line conductor.

conductor provided for safety purposes, for example protection against electric shock.

electrical conductor connected to the mid-point and able to take part in the distribution of electrical energy.

state of two or more conductive parts touching accidentally or intentionally, forming a single continuous conductive path.

maximum value of the electric current that can permanently flow through a conductor, a device or an apparatus, without its steady-state temperature, under given conditions, exceeding the specified value.

electric current passing through the body of a human or of an animal when it is in contact with one or more accessible parts of an electrical installation or with live electrical equipment.

electric current appearing in a protective conductor, such as the leakage current or the electric current resulting from an insulation fault.

specified value of the electric current that is intended to cause the operation of the protective device within a specified time.

electric current flowing as a result of an insulation fault.

phasor sum of the values of the electric currents in all the live conductors, at the same instant, at a given point of an electrical circuit in an electrical installation.

electric current that, under normal operating conditions, flows along an unwanted electrical path.

electric current intended to be carried by a circuit in normal operation for an unlimited time

electric current in a determined short circuit.

electric current intended to be carried in an electrical circuit in normal operation.

overcurrent occurring in an electrical circuit that is not due to a short-circuit current or to an earth fault.

leakage electric current in the ground or in metallic structures buried in the ground, resulting from their intentional or unintentional earthing.

fatal electric shock.

all the activities comprising the work necessary to enable the electrical installation to function. These activities cover areas such as: switching, control, monitoring and maintenance, both for electrical and non-electrical work.

repeated and uncoordinated contractions of individual muscle fibres.

cardiac fibrillation limited to the ventricles, causing a circulatory deficiency and then cardiac arrest.

passage with dimensions that allow persons to move freely along its entire length, fitted with supports for cables and their junctions with other elements of the electrical wiring system.

impedance at a given frequency between a specified point of a network, of an installation or of equipment and the reference earth.

examination of an electrical installation using all the senses in order to ascertain whether the choice of electrical equipment is correct and its mounting is appropriate;

assembly of associated electrical equipment with coordinated characteristics in order to fulfil a given purpose.

assembly of electrical connections and devices that form part of the earthing of a network, of an installation or of equipment.

insulation of hazardous live parts that provides basic protection

insulation comprising both basic insulation and supplementary insulation.

insulation of hazardous live parts that provides a degree of protection against electric shock equivalent to that of double insulation.

independent insulation provided in addition to basic insulation, for protection in the event of a fault.

application of specified stresses to an electrical installation by means of which its functionality is proven.

automatic interruption of a conductive line through the automatic operation of a protective device in the event of a fault.

short interruption during operation for purposes such as: connection, control, adjustment or observation of electrical equipment.

short interruption used for access to electrical equipment for maintenance.

opening of a switching device intended to interrupt the electrical supply of an electrical installation in order to avoid or reduce a hazard.

see circuit-breaker

device intended to close or interrupt the current in one or more circuits

switch designed to also ensure the isolation of the installation, or of a part of it, from the supply.

establishment of an electrical connection between conductive parts in order to achieve equipotentiality.

equipotential bonding made for safety purposes.

equipotential bonding made for functional purposes other than safety.

establishment of an electrical connection between a given point of a network, of an electrical installation or of equipment and a local earth.

earthing of one or more points of a network, of an installation or of equipment for purposes other than safety.

action of earthing one or more points of a network, of an installation or of equipment, for safety purposes.

action of earthing one or more points of an electrical network, in order to provide the functions of functional earthing and of protective earthing.

any work during which the worker deliberately comes into contact with live parts or deliberately enters the live working zone, either with a part of the body or with tools, equipment or devices that he handles.

accessible conductive part of an equipment that can be touched and that is not normally live, but which can become live following a fault in the basic insulation.

space which, under normal conditions, is characterized simultaneously by the following conditions: • relative humidity of the air at most 75%, at an air temperature between 15 °C and 30 °C; • insulating floor (location). It is synonymous with a low-hazard (or normal) workplace.

space characterized by at least one of the following conditions: • relative humidity of the air above 75% but at most 97% at an air temperature above 30 °C but at most 35 °C; • floor with conductive properties (for example concrete, earth); • conductive part in electrical connection with earth occupying at most 60% of the handling zone; • presence of conductive dusts (for example metal filings, graphite, etc.); • presence of fluids that reduce the impedance of the human body. It is synonymous with a hazardous workplace.

space characterized by at least one of the following conditions: • relative humidity of the air above 97% at an air temperature above 35 °C; • conductive parts in electrical connection with earth occupying more than 60% of the handling zone; • presence of corrosive agents. It is synonymous with a highly hazardous workplace.

the combination of all technical and administrative actions, including supervision actions, intended to keep an item in, or restore it to, a state in which it can perform a required function.

an element that prevents an unintentional direct contact, but does not prevent direct contact through a deliberate action.

an action intended to stop, as quickly as possible, an operation that has become dangerous.

the point at which electrical energy is delivered to an electrical installation.

a conductor or conductive part intended to be energized in normal operation, including the neutral conductor (N), but by convention excluding the PEN conductor, the PEM conductor or the PEL conductor.

a conductive part of equipment that can be touched and that is not normally live, but which may become live in the event of a failure of the basic insulation.

a cable support consisting of a continuous base with raised edges, but which is not provided with a cover.

the part of the Earth in electrical contact with an earth electrode and whose electric potential is not necessarily equal to zero.

the part of the Earth considered as conductive, whose electric potential is by convention taken as equal to zero, and which is outside the zone of influence of any earthing arrangement.

conductors or conductive parts that can be touched simultaneously by a person or an animal.

a risk of bodily harm caused by an electrical installation.

a person with relevant training and experience enabling them to foresee the risks and avoid the dangers that electricity can produce.

a person sufficiently informed, or supervised by skilled persons in the electrical field, so as to be able to foresee the risks and avoid the dangers that electricity can cause.

a person who is neither a skilled person nor an instructed person.

the maximum value of the electric current passing through a person’s body at which that person is still able to release themselves on their own.

the minimum value of the electric current through the body of a person or an animal that produces a specific sensation for that person or that animal.

a rigid or flexible sheet made of electrically insulating material, used to cover elements that are or are not live and/or adjacent parts, in order to prevent accidental contact.

a conductive part that may be embedded in the ground or in a specific conductive medium, for example concrete or coke, in contact with the earth.

an earth electrode sufficiently remote from other earth electrodes so that its electric potential is not significantly affected by the electric currents flowing between earth and the other earth electrodes.

an earth electrode embedded in the ground beneath the foundation of a building, or preferably in the concrete of the building’s foundation, generally in the form of a loop.

an earth electrode of an installation or of an item of equipment for safety purposes.

protection against electric shock in the absence of a fault. Basic protection corresponds to protection against direct contact.

protection against electric shock under single-fault conditions. Fault protection corresponds to protection against indirect contact.

a set of measures that reduce the risk of electric shock

a protective measure additional to basic protection and/or fault protection.

the common point between two symmetrical elements of a circuit whose extremities are electrically connected to the different line conductors of the same circuit.

the common point of a star-connected polyphase network, or the earthed midpoint of a single-phase network.

an equipotential network that provides a functional equipotential bonding.

the interconnection of conductive parts, which allows an equipotential bonding to be ensured between these parts.

an equipotential bonding network that provides a protective bonding.

the real part of the earthing impedance.

the part of an earthing arrangement that comprises only the earth electrodes and their interconnections.

a combination of the probability of occurrence and the severity of possible injury or harm to the health of a person exposed to one or more hazards.

an electrical network whose voltage does not exceed the extra-low voltage value: • under normal conditions and • under fault conditions, except for earth faults in other electrical circuits

an electrical network whose voltage does not exceed the extra-low voltage value: • under normal conditions and • under fault conditions, including an earth fault in other electrical circuits

an accidental or intentional conductive path between two or more conductive parts such that the difference in electric potential between these conductive parts is zero or approximately zero.

a function intended to de-energize an electrical installation or a part of it, separating the electrical installation from any source of electrical energy for safety purposes.

a protective measure in which the hazardous live parts are insulated from all other electrical circuits, from the local earth and from any contact.

separation between two electrical circuits by means of: • double insulation • basic insulation together with electrical protection by means of a screen, or • reinforced insulation

separation between electrical circuits or between an electrical circuit and the local earth by means of basic insulation.

a switching device that, in the open position, satisfies the specific requirements for the isolating function.

an electrical supply system for maintaining the operation of equipment and electrical installations that are important: • for the health and safety of persons and domestic animals, and/or • for avoiding damage to the environment and to other equipment, where this is required by national regulations.

a closed protective assembly, of circular cross-section or not, for insulated conductors, cables and cords, allowing them to be installed and replaced by drawing-in, used in electrical installations.

a closed protective system, provided with a base and a removable cover, intended for the complete protection of insulated conductors and cables and/or for the accommodation of other electrical equipment, including information-processing equipment.

an assembly consisting of several insulated electrical conductors, cables or busbars and the elements that ensure their fixing and, if necessary, their mechanical protection.

a physiological effect resulting from the passage of an electric current through the body of a person or an animal.

an assembly comprising different types of switchgear associated with one or more outgoing electrical circuits, fed by one or more incoming circuits, together with terminals for the neutral and protective conductors.

the voltage between conductive parts touched simultaneously by a person or an animal.

the voltage appearing between simultaneously accessible conductive parts when these conductive parts are not being touched by a person or an animal.

the voltage between a fault point and the reference earth, as a result of an insulation fault.

a voltage that does not exceed the limits specified for band I given in SR CEI 60449.

the nominal value of the voltage by which the electrical installation or a part of the electrical installation is named and identified.

the voltage between two points on the surface of the Earth located 1 m apart from each other, taken to be the length of a person’s step.

all the measures by which the conformity of electrical installations with the requirements in force is checked.

an area accessible only to skilled persons (in the electrical field) and instructed persons (in the electrical field).

the space extending between any point of a surface where persons usually stand or move and the limit that a person can reach with the hand, in all directions, without auxiliary means.

the place (places), location (locations) or surface (surfaces) where the work will be, is being or has been carried out.

the space around live parts at which the level of insulation for preventing electric shock is not ensured when entering it without protective measures.

a delimited space surrounding the live working zone.

automatic transfer to the standby supply;

residual current protective device;

lightning protection installation;

a network with the neutral point of the transformer isolated from earth (or through a very high value impedance) and the exposed-conductive-parts earthed;

neutral conductor;

lightning protection by means of an early streamer emission device;

protective conductor;

combined protective and neutral conductor;

device for protection against overvoltages and/or for diverting lightning current;

lightning protection system;

protective extra-low voltage (PELV);

safety extra-low voltage (SELV);

a network with the neutral point of the transformer earthed and a conductor with combined functions: protective and neutral;

a network with the neutral point of the transformer earthed and separate conductors for the protective and neutral functions;

a network in which the protective and neutral conductor functions are combined in a single conductor over the first part of the network.

a network with the neutral point of the transformer earthed and the exposed-conductive-parts connected to independent earth electrodes.