| C | rating factor – general |
| 0-10V | 0 to 10 Volt Signal |
| A | Ampere, the unit of electrical current. |
| A/C | Air Conditioning |
| AC | Alternating Current, a type of electrical current that periodically reverses direction. |
| ADC | Analog to Digital Converter |
| AFCI | Arc Fault Circuit Interrupter |
| AFDD | Arc-fault-detection device |
| AHU | Air Handling Unit |
| AIC | Ampere Interrupting Capacity |
| AIS | Air Insulated Switchgear |
| AL | Aluminum |
| ATC | Automatic Temperature Control |
| ATS | Automatic Transfer Switch |
| AUTO | Automatic |
| AVR | Automatic Voltage Regulator |
| AWG | American Wire Gauge |
| BC | bayonet cap |
| BMS | Building Management System |
| BN | Bonding network |
| BRC | Bonding ring conductor |
| BREEAM | Building Research Establishment Environmental Assessment Methodology |
| BSI | British Standards Institution |
| BTU | British Thermal Units |
| C | Conduit |
| C SPD | Class C surge protective device (IEC 61643) |
| c.s.a | cross-sectional area |
| C/B | Circuit Breaker |
| Ca | rating factor for ambient temperature |
| CAN | Controller Area Network |
| CATV | Cable Television or Community Antennae Television |
| CB | Critical Branch |
| CBN | Common bonding network |
| CBR | Circuit-breaker incorporating residual-current protection |
| Cc | rating factor for circuits buried in the ground |
| CCT | Circuit (also: CIR, CKT) |
| CCTV | Closed Circuit Television |
| Cd | rating factor for depth of burial |
| CD | Candela |
| CFL | Compact Fluorescent Lamp |
| Cg | cable grouping correction factor |
| Ci | rating factor for thermal insulation around cable |
| CIR | Circuit (also: CCT, CKT) |
| CKT | Circuit (also: CCT, CIR) |
| CLF | Current Limiting Fuse |
| CNE | combined neutral and earth |
| COM | Common |
| COS | Cosine |
| cos 0 | power factor (sinusoidal systems) |
| cos ϕ | power factor, i.e. kW input / kVA input |
| CPC | circuit protective conductor |
| CPS | Control & protective switching device |
| CPT | Control Power Transformer |
| CPU | Central Processing Unit |
| Cs | rating factor for soil thermal resistivity |
| Ct | correction factor for the conductor operating temperature |
| CT | Current Transformer |
| CU | Consumer Unit, also known as a fuse box or distribution board. |
| Cu | Copper |
| DAC | Digital to Analog Converter |
| DB | Distribution Board, a component of an electrical system that distributes electricity to various circuits. |
| dB | Decibel |
| DC | Direct Current, a type of electrical current that flows in one direction. |
| DC BN | Direct current bonding network |
| DCL | Device for Connecting a Luminaire |
| DG | Diesel Generator |
| DOL | Direct On Line |
| DP | Double Pole |
| e.m.f. | electro-motive force |
| EAF | Exhaust Air Fan |
| EB | Equipment Branch |
| EC | Electrical Code or Electrical Contractor |
| ECA | Electrical Contractors Association |
| EDW | Electrodynamic withstand (EDW): Capacity of a unit to tolerate, by nature of its construction, the electrodynamic effects of a short-circuit current, in particular without repulsion of its main or plug-in contacts. |
| EEBAD | earthed equipotential bonding & automatic disconnection |
| EEMS | Electrical-Energy Management System |
| EEPROM | Electrically Erasable Programmable Read Only Memory |
| EF | Exhaust Fan |
| EIC | Electrical Installation Certificate, a document confirming the safe installation of electrical work. |
| ELCB | Earth Leakage Circuit Breaker |
| ELV | Extra Low Voltage, typically voltages below 50V AC or 120V DC. |
| EM | Emergency |
| EMC | Electromagnetic compatibility |
| EMF | Electromotive Force |
| EMI | Electromagnetic interference |
| EMS | Energy Management System |
| EMT | Electrical Metallic Tubing |
| ENA | Energy Networks Association (UK) |
| EP | Emergency Power |
| EPO | Emergency Power Off (Button or Switch) |
| EPR | Earth potential rise |
| ES | edison screw |
| EV | Electric vehicle |
| EVO | Efficiency Evaluation Organization |
| EWC | Electric Water Cooler |
| F | Farads |
| f | frequency |
| F | Fuse |
| FA | Fire Alarm |
| FAA | Fire Alarm Annunciator |
| FCU | Fused Connection Unit, a type of electrical fitting containing a fuse for circuit protection. |
| FELV | Functional extra-low voltage |
| FFT | smoothing, classification, statistics |
| FIELDBUS | Field Bus |
| FLA | Full Load Amps & FLC= Full Load Current - They basically mean the same thing. |
| FLC | full load current |
| FMC | Flexible Metal Conduit |
| G | Ground |
| GFP | Residual Sensing ground fault protection[1] (Sensitivity 20% -100% circuit breaker rating) |
| GHz | gigahertz (1 GHz = 1,000,000,000 Hz) |
| GIS | Gas Insulated Switchgear |
| GN | guidance note |
| GND | Ground |
| GNYE | Green-and-yellow (conductor colour) |
| GRMC | Galvanized Rigid Metal Conduit |
| h | Net Head, also related to hydro power generation. |
| H | Henry |
| HBC | high breaking capacity (fuse) |
| HD | Harmonization Document (CENELEC) |
| HF | High frequency |
| HMI | Human Machine Interface |
| HOA | Hand-Off-Automatic Switch |
| HQE | Haute Qualité Environnementale |
| HRC | high rupturing capacity (fuse) |
| HSE | Health and Safety Executive |
| HVAC | Heating, Ventilation, Air Conditioning |
| Hz | Hertz, the unit of frequency, representing cycles per second. |
| I | Common symbol for current in mathematical formulas |
| I CR | short-time threshold |
| I/O | Input/Output |
| I0 | The base current setting (I0), which determines the approximate overload setting. The adjustment is related to the rated current ( ) of the MCCB |
| I2 | current ensuring effective operation of the protective device is given in the product standard or may be provided by the manufacturer. |
| Ia | current to operate protective device |
| Ib | design current of the circuit (present‐day load) |
| IBN | Isolated bonding network |
| ICB | Instantaneous-trip circuit-breaker |
| Icm | Close and Latch Rating |
| Icn | is the rated short-circuit capacity (marked on the device). Icn is the maximum fault current the breaker can interrupt safely, although the breaker may no longer be usable. |
| Ics | is the service short-circuit capacity. Ics is the maximum fault current the breaker can interrupt safely without loss of performance, given as a peak value, actually crossing the circuit-breaker, taking account of any limitation. |
| Icu | Ultimate breaking capacity: This is the usual name for the ultimate breaking capacity (Icu). Icu is the highest short-circuit current intensity which the circuit-breaker is able to interrupt. It is defined for a given rated operating voltage Ue. |
| Icw | Short-time withstand current. This is the maximum short-circuit current (as an rms value), which the circuit-breaker can withstand for a defined period (0.5 or 1 or 3 s) without alteration of its characteristics. |
| Id | fault current |
| IDMT | Inverse Definite Minimum Time |
| IDMTL | (Inverse Definite Minimum Time Lag) This refers to long-time delay curves where the slope can take different values |
| Ifi | follow-on current interrupt rating of SPD |
| IG | Isolated Ground |
| Ik | rated short-time withstand current (r.m.s.) of equipment |
| ILP | Institution of Lighting Professionals |
| Im | Short-circuit protection (short time) Tripping thresholds, The short-time current setting which performs essentially the same function as the magnetic short-circuit current setting of a thermal and magnetic trip unit The short-time current setting (Im)‡, for which the adjustment relates to the long-time current setting ( ) |
| IMC | Intermediate Metal Conduit |
| IMD | Insulation-monitoring device |
| IMPR | electronic device |
| In | rated current or current-setting of protective device |
| In | rated (nominal) current or current setting of the protective device corresponding to the maximum trip unit setting & Instantaneous release : Release without intentional time delay (short-circuit protection). |
| INT | Interlock |
| INU | Insulation neutral unit |
| Ip | rated peak withstand current of equipment |
| Ip | Prospective short-circuit current which would develop in the absence of protective devices (rms value). |
| IP (code) | Ingress-Protection code to BS EN 60529 |
| Ipf | prospective fault current at a point in the installation |
| Ir | Overload protection (long time) Tripping thresholds - overload setting of the protective device or Current (as rms value) corresponding to the overload protection setting. Generaly varies from 0.4 to 1 times. Its the long-time current setting, which determines the fine overload setting. The adjustment relates not to the rated current ( ) of the MCCB (as it does where thermal and magnetic protection is provided), but to the base current setting ( ). |
| Irm | motor overload setting |
| Isc (STC) | short-circuit current of a PV module/string/array under standard test conditions |
| Isccr | short-circuit current rating of SPD + OCPD combination |
| It | current-carrying capacity under installation conditions |
| It | tabulated current |
| IT | earthing system (see 5.2.6) |
| IT | Isolated Terra (Isolated Neutral) |
| IT system | Unearthed LV supply system |
| Iz | current-carrying capacity of a cable for continuous service |
| IΔn | rated residual operating current of an RCD |
| k | kilo - one thousand times |
| kA | kiloampere (1 kA = 1000 A) |
| kA Ics | service short-circuit breaking capacity of CB |
| kA Icu | ultimate short-circuit breaking capacity of CB |
| kA Icw | short-time withstand current of switchgear (1 s unless stated) |
| kHz | kilohertz (1 kHz = 1000 Hz) |
| kV | kilovolts (1 kV = 1000 V) |
| kV | kilovolt (1000 V) |
| kV Ud | rated power-frequency withstand voltage of equipment |
| kV Ur | rated insulation voltage of equipment |
| kVA | Kilovolt-ampere, a unit of apparent power. |
| kVA | Kilovolt-Ampere |
| KVAR | Kilovolt-Amperes Reactive |
| kW | Kilowatt, a unit of power equal to 1000 watts. |
| kW | Kilowatt |
| kΩ | Kilo-ohm (1 kΩ = 1000 Ω) |
| LDR | Light Dependent Resistor |
| LED | Light-emitting diode |
| LED | several watts per component |
| LFMC | Liquid Tight Flexible Metal Conduit |
| LIMS | Lighting Management System |
| LRA | Locked Rotor Amp |
| LSC | Luminaire supporting coupler |
| Lt | Long-time delay release (LT): Release with intentional time delay lasting several seconds (overload protection). This delay is generally dependent on the current. |
| LTG | Lighting |
| LV | Low voltage (50 V – 1 000 V ac) |
| m | metre |
| m | milli - one thousandth part of |
| M | meg or mega - one million times |
| m.i. | mineral-insulated |
| mA | Milliampere, one-thousandth of an ampere. |
| mA | Milliampere = (1000 mA = 1 A) |
| mA | milliampere |
| MAN | Manual |
| MAX | UOC = Open Circuit Voltage |
| MC | Metal Clad Cable |
| MCA | Min. Circuit Amps (Amp) |
| MCB | Miniature Circuit Breaker |
| MCC | Motor Control Center |
| MCCB | Moulded Case Circuit Breaker |
| MCP | Motor Circuit Protection |
| MD | maximum demand |
| MEN | Multiple Earthed Neutral |
| MESH-BN | Meshed bonding network |
| mH | millihenry (1000 mH = 1 H) |
| MHz | megahertz (1 MHz = 1,000,000 Hz) |
| MI | Mineral Insulated |
| MLO | Main Lugs Only |
| MLVS | Prisma P |
| MODBUS | Serial Communication Protocol |
| MOP | Max Overcurrent Protection (Amp) |
| MPP | Maximum Power Point |
| MRCD | Modular residual-current device |
| mS | Millisiemen (1000 mS = 1 S) |
| MSC | Max Starting Current (Amp) |
| MTBF | Mean Time Between Failure |
| MTS | Manual Transfer Switch |
| MTTR | Mean Time To Repair |
| mV | millivolts (1000 mV = 1 V) |
| mW | milliwatt (1000 mW = 1 W) |
| MW | megawatt (1 MW = 1,000,000 W) |
| MW | Megawatt |
| MΩ | Megaohm, one million ohms. |
| MΩ | Megaohm (1 MΩ = 1,000,000 Ω) |
| N/C | Normally Closed |
| N/O | Normally Open |
| NC | Normally Closed |
| NC | Normally Closed |
| NEC | National Electrical Code |
| nF | nanofarads (1,000,000,000 nF = 1 F) |
| NL | Night Light |
| NO | Normally Open or Number |
| NO | Normally Open |
| OC Device | Over-current device |
| OCPD | Over-current protective device |
| OPC | OLE for Process Control |
| P | Pole |
| P&ID | Piping and Instrumentation Diagram |
| p.d. | potential difference |
| p.v.c. | poly-vinyl chloride |
| PB | Push Button or Panic Button or Pull Box |
| PCB | PolyChlorinated Biphenyl |
| PE | Protective conductor |
| PEC | Z sup |
| PEI | Prosumer’s LV electrical installation |
| PEL | Function-combined protective and live conductor (dc) |
| PELV | Protective extra-low voltage |
| PEN | Combined protective-earth and neutral conductor |
| pF | picofarads (1,000,000,000,000 pF = 1 F) |
| PF | Power Factor |
| PID | Proportional Integral Derivative |
| PIR | passive infra-red detector |
| PLC | Programmable Logic Controller |
| PMD | Power Meters |
| PME | Protective multiple earthing (UK TN-C-S supply) |
| Pn | nominal power (in kW) |
| PNL | Panel |
| PPE | Personal protective equipment |
| PQI | Power Quality Instruments |
| PROFIBUS | Process Field Bus |
| PSC | prospective short-circuit current |
| PT | Potential Transformer |
| PV | Photovoltaic (solar) |
| PWM | Pulse Width Modulation |
| PWR | Power |
| Q (SPD) | total charge (coulombs) associated with SPD impulse test |
| R | resistance (electrical) |
| r.m.s. | root-mean-square (effective value) |
| R1 | resistance of line conductor (origin to load point) |
| R1+R2 | sum of line and CPC resistances (continuity test value) |
| R2 | resistance of circuit protective conductor (origin to load point) |
| r20 | resistivity of conductor at 20 °C |
| Ra | the total resistance of the earth electrode and the protective conductor onnecting it to exposed conductive parts |
| RAF | Return Air Fan |
| RAM | Random Access Memory |
| RCBO | RCD with integral over-current protection |
| RCD | Residual-current device (RCCB or RCBO) |
| REQ | Required |
| RLA | Rated Load Amps (Amp) |
| RMC | Rigid Metal Conduit |
| RMS | Root Mean Squared |
| RNC | Rigid Non-Metallic Conduit |
| ROM | Read Only Memory |
| Rp | prospective rise of earth potential (EPR) |
| Rp | resistance of the human body |
| RTU | Remote Terminal Unit |
| s | cross-sectional area of a conductor (mm²) |
| SAF | Supply Air Fan |
| SCADA | Supervisory control and data acquisition |
| SCPD | ShortCircuit Protective Device |
| SD | Star Delta |
| SE | Service Entrance |
| SEB | Service End Line Box or Service Electrical Box |
| SELV | seperated extra-low voltage |
| SEN | Separate earth and neutral (TN-S) |
| SIS | Solid Insulated Switchgear |
| sk | cross-sectional area of conductor k (parallel runs) |
| SLD | Single Line Diagram |
| SP | Spare |
| SPD | Surge protective device |
| SPDT | Single Pole Double Throw |
| SPE | or PEN |
| SPST | Single Pole Single Throw |
| ST | Shunt Trip |
| STS | Static transfer switch |
| SVHC | Substances of Very High Concern |
| SW | Switch |
| SYM | Symmetrical |
| t | time |
| TEL | Telecommunications, Telephone |
| THD | Total Harmonic Distortion |
| TMCB | Thermal Magnetic Circuit Breaker |
| TN | Terre Neutre (Earthed Neutral) |
| TN-C | LV system with combined neutral & PE throughout |
| TN-C-S | earthing system (see 5.2.4) |
| TN-S | LV system with separate neutral & PE throughout |
| TOV | Temporary over-voltage |
| tp | maximum permitted normal operating conductor temp. (°C) |
| tr | The long-time delay setting (tr), which allows the speed of response of the overload portion of the time / current characteristic to be adjusted. This is the delay in seconds before the MCCB will be tripped when a steady current equal to a certain multiple of the long-time current setting ( ) is flowing. |
| TSO | Transmission System Operator |
| TT | LV system with consumer earth electrode, supply earth separate, Terre Terre (Earthed) |
| U | symbol for voltage (alternative for V) |
| U0 | Voltage to earth of LV system |
| Uac | alternating voltage |
| Uc | continuous operating voltage of SPD mode of protection |
| Udc | direct voltage |
| Ue | Rated Operational voltage |
| UG | Under Ground |
| Ui | Rated Insulation voltage |
| Uimp | Rated impulse withstand voltage |
| UL | Underwriters Laboratory |
| Uo | phase voltage |
| Uo-c | open-circuit voltage of PV string/array |
| Up | SPD rated limiting (protection) voltage |
| UPS | Uninterruptible power supply |
| Utν | temporary over-voltage (power-frequency, kV) |
| Uw | rated impulse-withstand voltage of equipment insulation |
| V | Volt, the unit of electrical potential or voltage. |
| VA | Volt-Ampere, a unit of apparent power. |
| VAC | Alternating Current Voltage |
| VDC | Volts, direct current. |
| VFD | Variable Frequency Drive |
| VPN | Virtual Private Network |
| VT | Voltage Transformer |
| W | watt - unit of power |
| WH | Water Heater |
| WHO | World Health Organisation |
| WP | Weatherproof or Waterproof |
| X | reactance |
| Z | Impedance (measured in Ω) |
| Zdb | earth-fault loop impedance at a distribution board |
| Zdb | earth-fault loop impedance at distribution board |
| Ze | external earth-fault loop impedance (supply) |
| Zs | earth-fault loop impedance of a circuit |
| α | temperature coefficient of resistance of copper |
| η | per-unit efficiency, i.e. output kW / input kW |
| λ | thermal resistivity of soil (K·m/W) |
| λW | specific energy (J/Ω) in SPD impulse definition |
| μA | microampere (1,000,000 μA = 1 A) |
| μF | microfarads (1,000,000 μF = 1 F) |
| μH | microhenry (1,000,000 μH = 1 H) |
| Φ | Phase |
| Ω | Ohm, the unit of electrical resistance. |
| Ω | Ohm |
| Ω | Ohm |
| ΩT | earthing-system resistance target value |
