Earthing, Bonding, and Testing

Comprehensive practice flashcards defining essential vocabulary and technical concepts in earthing, bonding, protective devices, and testing according to Irish and European electrical installation standards.

System Earthing

The intentional connection of a point in the electrical power system, usually the neutral point of a generator or transformer, to earth through a conductor or earthing impedance to provide a reference potential, limit overvoltages, and ensure power system stability.

Equipment Earthing

The intentional connection of all exposed, non-current-carrying conductive metal parts of electrical equipment (such as frames, enclosures, and cable trays) to earth through a low-impedance conductor to ensure safe passage of fault current and protect people from electric shock during an insulation failure.

Main Earthing Terminal (MET)

A terminal or brass bar provided in an installation for connecting together protective conductors, main equipotential bonding conductors, earthing conductors, and functional earthing conductors to the means of earthing.

Earthing Conductor

A protective conductor having green/yellow insulation that connects the Main Earthing Terminal (MET) directly to the earth electrode.

Main Protective Conductor

The neutralizing conductor in a TN-C-S installation that connects the Main Earthing Terminal (MET) to the incoming supply neutral (PEN conductor), typically located within the meter cabinet.

Circuit Protective Conductor (CPC)

A protective conductor connecting the exposed conductive parts of equipment to the Main Earthing Terminal to provide a low-impedance return path for earth fault current.

PEN Conductor

An earthed electrical conductor combining the dual functions of a protective conductor ($\text{PE}$) and a neutral conductor ($\text{N}$).

Earth Electrode

A conductive part or group of conductive parts placed in intimate contact with the ground to provide an effective electrical connection with the general mass of earth.

Domestic Earth Electrode Standard

A hot-dip galvanized-steel rod or pipe with a diameter of at least $16\,\text{mm}$, driven vertically into the ground to a depth of at least $1200\,\text{mm}$.

Resistance Area of an Earth Electrode

The ground area surrounding an earth electrode across which a voltage gradient exists during an earth fault, typically extending outward to approximately $2.5\,\text{m}$ where no further increase in resistance is measured.

Neutral Inversion

A dangerous phenomenon occurring when the supply PEN conductor breaks, causing the installation's neutral conductor and all bonded earthed metalwork to rise to the full phase potential ($230\,\text{V}$) with respect to earth.

Equipotential Bonding

Electrical connections designed to maintain exposed conductive parts and extraneous conductive parts at substantially the same potential to prevent dangerous touch voltages from appearing between them during a fault.

Main Equipotential Bonding

The bonding of incoming metallic engineering services (gas, water, oil pipes, central heating, air-conditioning ducts, and structural steel) to the MET using copper conductors of not less than $10\,\text{mm}^2$ (or half the CSA of the largest protective conductor).

Supplementary Equipotential Bonding

Local bonding applied within high-risk areas (such as bathrooms) that interconnects all exposed and extraneous conductive parts using insulated copper conductors of at least $2.5\,\text{mm}^2$ (if mechanically protected) or $4\,\text{mm}^2$ (if unprotected).

Direct Contact

The contact of persons or livestock with parts of an electrical installation that are normally live.

Indirect Contact

The contact of persons or livestock with exposed conductive parts or extraneous conductive parts that are not normally live, but have become live due to an insulation failure or internal fault.

EEBADS

An acronym standing for Earthed Equipotential Bonding and Automatic Disconnection of Supply, a primary protective method against electric shock.

TN-C-S System

An earthing system where the neutral and protective functions are combined into a single PEN conductor from the supply source to the entry point, and separated into distinct neutral ($\text{N}$) and protective ($\text{PE}$) conductors within the consumer installation.

TN-S System

An earthing system having separate protective ($\text{PE}$) and neutral ($\text{N}$) conductors throughout both the supply network and the installation.

TN-C System

An earthing arrangement in which the neutral and protective functions are combined into a single conductor (PEN) throughout both the supply network and the installation.

TT System

An earthing system where the source is directly earthed and the exposed conductive parts of the installation are connected to an independent consumer earth electrode with no supply-provided protective path, requiring an RCD for fault protection.

IT System

An earthing system where the source has no connection to earth (isolated) or is connected via a high impedance, while exposed conductive parts are connected to an independent installation earth electrode, ensuring power continuity on a first fault.

Earth Fault Loop Impedance ($Z_s$ or $Z_L$)

The total impedance of the complete closed path traversed by fault current during a phase-to-earth fault, determined by the formula $Z_s = Z_e + (R_1 + R_2)$.

External Earth Fault Loop Impedance ($Z_e$)

The impedance of the supply network external to the installation, comprising the supply transformer secondary winding, the phase service conductor, and the supply return path/PEN conductor.

Class I Equipment

Electrical equipment having basic insulation throughout that relies on the earthing of exposed conductive parts via a protective conductor for protection against indirect contact.

Class II Equipment

Electrical equipment constructed with double or reinforced insulation throughout that does not require and must not be connected to a protective earth conductor.

Class III Equipment

Equipment designed to operate exclusively from a Separated Extra-Low Voltage ($\text{SELV}$) supply in which internal voltages higher than extra-low voltage are not generated.

Separated Extra-Low Voltage (SELV)

An extra-low voltage system ($\le 50\,\text{V a.c.}$ or $\le 120\,\text{V d.c.}$) fed from a safety isolating transformer, completely electrically isolated from earth and other electrical systems.

Protective Extra-Low Voltage (PELV)

An extra-low voltage system ($\le 50\,\text{V a.c.}$ or $\le 120\,\text{V d.c.}$) electrically separated from higher voltages by double or reinforced insulation, but having one point on the circuit intentionally connected to earth for functional purposes.

Functional Extra-Low Voltage (FELV)

An extra-low voltage system that does not meet the safety requirements of SELV or PELV, such as lacking double or reinforced insulation between its secondary circuit and low-voltage primary windings.

Reduced Low Voltage (RLV)

A site safety supply system operating at $110\,\text{V a.c.}$ supplied from a double-wound transformer with an earthed secondary centre-tap, limiting maximum shock exposure to $55\,\text{V a.c.}$ to earth on single-phase outlets.

Residual Current Device (RCD)

A mechanical switching device intended to interrupt supply when the vector algebraic sum of the instantaneous live currents (the residual operating current $I_{\Delta n}$) reaches a set threshold.

Type S RCD

A time-delayed residual current device installed upstream to achieve selectivity and prevent tripping before downstream general-type RCDs operate.

Arc Fault Detection Device (AFDD)

A microprocessor-based protective device fitted at the origin of a final circuit to analyse current waveforms and disconnect the circuit upon detecting series or parallel electrical arcing signatures, mitigating fire risk.

Surge Protection Device (SPD)

A device designed to protect consumer units, electrical wiring, and sensitive electronic equipment against transient overvoltages by limiting voltage spikes and diverting surge currents safely to earth.

Calculated Risk Level (CRL)

A risk-assessment formula value for transient overvoltages; protection against atmospheric surges is mandatory if $CRL < 1000$, but not required if $CRL \ge 1000$.

Fall of Potential Method

An earth electrode resistance measurement method (Annex 6C, Method C1) utilizing two auxiliary test electrodes (potential spike and current spike) placed at specified distances from the main electrode under test.

Denso Tape

A waterproof petrolatum-impregnated tape applied over the earth electrode clamp connection to prevent chemical degradation, electrolytic corrosion, and moisture ingress.

Safety Electrical Connection Label

A permanent embossed metallic label bearing the inscription 'SAFETY ELECTRICAL CONNECTION - DO NOT REMOVE' that must be affixed to all main and supplementary bonding pipe clamps and electrode inspection boxes.

Bathroom Zone 0

The interior space of a bathtub or shower tray where installed equipment must achieve an ingress protection rating of at least IPX7 (protection against temporary immersion).

Adiabatic Equation for Protective Conductors

The formula $S = \frac{\sqrt{I^2 t}}{k}$ used to determine the minimum cross-sectional area ($S$) of a protective conductor based on prospective fault current ($I$), disconnection time ($t$), and conductor material factor ($k$).