MEP Abbreviations & Acronyms Reference
Commonly used, electrically biased MEP abbreviations and acronyms.
| ID | Description |
|---|---|
| 0-10V | 0 to 10 Volt Signal |
| 1G | One Gang (outlet/switch plate) |
| 2G | Two Gang (outlet/switch plate) |
| 2W | Two Way (switch wiring) |
| 4P+E | Four Poles and Earth (connector) |
| A | Ampere, the unit of electrical current. |
| A/C | Air Conditioning |
| AAV | Air Admittance Valve |
| AC | Alternating Current, a type of electrical current that periodically reverses direction. |
| ACB | Air Circuit Breaker |
| ACDC | Access Control Door Controller |
| ACH | Air Changes per Hour |
| ACM | Asbestos Containing Material |
| ACO | Annual Cost of Ownership |
| ACoP | Approved Code of Practice (UK HSE guidance) |
| ACP | Access Control panel |
| ACR | Attenuation to Crosstalk Ratio |
| ACS | Access Control System server |
| ADC | Analog to Digital Converter |
| ADPI | Air Diffusion Performance Index |
| AEVA | Automated and Electric Vehicles Act 2018 |
| AFAS | Automatic Fire Alarm System |
| AFCB | Arc Fault Circuit Breaker |
| AFCI | Arc Fault Circuit Interrupter |
| AFDD | Arc-fault-detection device |
| AFE | Analogue Front End |
| AFFF | Aqueous Film-Forming Foam |
| AFFL | Above Finished Floor Level |
| AFP | Active Fire Protection |
| AFSS | Automatic Fire Suppression System |
| AGS | Anaesthetic Gas Scavenging system |
| Ah | Ampere-hour |
| AHC | Active Harmonic Conditioner |
| AHF | Active Harmonic Filter |
| AHJ | Authority Having Jurisdiction |
| AHU | Air Handling Unit. Central ventilation plant that conditions and distributes air (typically supply/extract), usually including fans, filters, heating/cooling coils, dampers and controls. |
| AIC | Ampere Interrupting Capacity |
| AICP | Asset Information Collection Plan |
| AIDA | Air Infiltration Development Algorithm |
| AIM | Asset Information Model |
| AIR | Asset Information Requirements |
| AIS | Air Insulated Switchgear |
| AJT | Average Journey Time (lift) |
| AL | Aluminum |
| AM | Applications Manual (CIBSE publication) |
| AMR | Automatic Meter Reading |
| Amtech | Electrical power distribution calculation software |
| AN-PD1 | Nurse Call Programmable Display |
| ANPR | Automatic Number Plate Recognition |
| ANSI | American National Standards Institute |
| AOV | Automatic Opening Vent (smoke control ventilation) |
| APFC | Automatic Power Factor Correction |
| APHC | Association of Plumbing and Heating Contractors |
| AQOLS | Air Quality Objective Levels |
| AR | Alcohol-Resistant foam |
| ARV | Automatic Air Release Valve |
| ASCS | Automatic Source-Changeover Systems |
| ASD | Aspirating Smoke Detector |
| ASDU | Aspirating Smoke Detector Unit |
| ASE | Annual Sunlight Exposure (daylight metric) |
| ASET | Available Safe Egress Time |
| ASHP | Air Source Heat Pump |
| ASP | Anti-Siphon vent Pipe |
| ATAP | Accessible Toilet Alarm Control Panel |
| ATC | Automatic Temperature Control |
| ATEX | Equipment/systems for use in potentially Explosive atmospheres |
| ATM | Asynchronous Transfer Mode |
| ATS | Automatic Transfer Switch |
| ATT | Average Transit Time (lift) |
| ATTD | Average Travel Time to Destination (lift) |
| AUTO | Automatic |
| AV | Audio Visual cabling and containment |
| AVAC | Audio Visual Access Control |
| AVE | Average (illuminance) |
| AVR | Automatic Voltage Regulator |
| AVSU | Area Valve Service Unit |
| AW | Above Work top (mounting level) |
| AWG | American Wire Gauge |
| AWT | Average Waiting Time (lift) |
| BA | Double Check Valve Assembly – backflow prevention type BA |
| BACnet | Building Automation and Control Network protocol |
| BAS | Building Automation System |
| BB | Broadband Socket Outlet + Connection |
| BC | bayonet cap |
| BCO | British Council for Offices |
| BCW | Boosted Cold Water pipework (artificially pressurised) |
| BEMS | Building Energy Management System |
| BEng | Bachelor of Engineering |
| BEP | BIM Execution Plan |
| BER | Building Emission Rate (Building Regulations Part L) |
| BESA | Building Engineering Services Association |
| BESS | Battery energy storage system |
| BG | Break Glass (security) |
| BHU | Bed Head Unit |
| BIG | Back Inlet Gully |
| BIM | Building Information Modelling |
| BIPV | Building Integrated Photovoltaic |
| BIS | Building Intercom System recorder |
| BIV | Butterfly Isolation Valve |
| BMR | Basal Metabolic Rate |
| BMS | Building Management System |
| BMU | Building Maintenance Unit |
| BN | Bonding network |
| BNO | Building Network Operator |
| BOC | Bottom of Containment |
| BOD | Biochemical Oxygen Demand |
| BOH | Back of House |
| BOT | Bottom (position reference, e.g. bottom of containment) |
| BPEC | Building and Plumbing Engineering Competencies |
| BRC | Bonding ring conductor |
| BRE | Building Research Establishment |
| BREEAM | Building Research Establishment Environmental Assessment Methodology |
| BRTD | Battery-less Ride-Through Device |
| BRUKL | Building Regulations UK Limit (Part L compliance software) |
| BS | British Standard |
| BSI | British Standards Institution |
| BSRIA | Building Services Research and Information Association |
| BST | British Summer Time |
| BT | Direct Incoming British Telecom Analogue Telephone Line |
| BTU | British Thermal Units |
| BU | Bench Unit mounted |
| BW | Below Work top (mounting level) |
| C | rating factor – general |
| 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 |
| CAD | Computer Aided Design |
| CAES | Compressed Air Energy Storage |
| CAFM | Computer Aided Facility Management |
| CAFS | Compressed Air Foam Systems |
| CAN | Controller Area Network |
| CAPEX | Capital Expenditure |
| CAT5 | Category 5 data cable |
| CAT5 (Pump) | Category 5 water pump |
| CAT5e | Category 5e data cable (enhanced) |
| CAT6 | Category 6 data cable |
| CAT6a | Category 6a data cable (augmented) |
| CAT7 | Category 7 data cable |
| CAT8 | Category 8 data cable |
| CATV | Cable Television or Community Antennae Television |
| CAV | Constant Air Volume ductwork terminal unit |
| CB | Critical Branch |
| CBEMA | Computer and Business Equipment Manufacturers Association |
| CBM | Condition Based Maintenance |
| CBN | Common bonding network |
| CBR | Circuit-breaker incorporating residual-current protection |
| CBS | Central Battery System |
| Cc | rating factor for circuits buried in the ground |
| CCHP | Combined Cooling, Heating and Power |
| CCS | Combined Charging Standard |
| CCT | Circuit (also: CIR, CKT) |
| CCTV | Closed Circuit Television |
| CCU | Cooker Control Unit |
| Cd | rating factor for depth of burial |
| CDC | Controlled Drugs Cupboard interface |
| CDE | Common Data Environment (BIM) |
| CDI | Corridor Display Unit Interface |
| CDM | Construction Design and Management Regulations |
| CdW | Condenser Water system (heat rejection) |
| CdW_F | Condenser Water Flow pipework |
| CdW_R | Condenser Water Return pipework |
| CE | Cleaning Eye (drainage access fitting) |
| CEN | European Committee for Standardization |
| CENELEC | European Committee for Electrotechnical Standardisation |
| CFCs | Chlorofluorocarbons (refrigerants) |
| CFD | Computational Fluid Dynamics (simulation) |
| CFL | Compact Fluorescent Lamp |
| CFM | Cubic Feet per Minute (ventilation flow rate) |
| CFSD | Combined Fire & Smoke Damper |
| CFSH | Code for Sustainable Homes |
| Cg | cable grouping correction factor |
| CHAdeMO | DC fast charging standard (Charge de Move) |
| CHP | Combined Heat and Power (cogeneration) |
| CHS | Circular Hollow Section (structural steel) |
| CHW | Chilled Water. Cooling water circuit serving AHU and FCU cooling coils or other cooling loads |
| ChW_F | Chilled Water Flow pipework |
| ChW_R | Chilled Water Return pipework |
| CHWP | Chilled Water Pump |
| Ci | rating factor for thermal insulation around cable |
| CIBSE | Chartered Institution of Building Services Engineers |
| CIE | International Commission on Illumination |
| CIE(M) | Fire Detection & Alarm Control & Indicating Equipment Main Panel |
| CIE(R) | Fire Detection & Alarm Control & Indicating Equipment Repeater Panel |
| CIR | Circuit (also: CCT, CKT) |
| CIRED | International Conference on Electricity Distribution |
| CISPR | International Special Committee on Radio Interference |
| CKT | Circuit (also: CCT, CIR) |
| CL | Cupboard Lighting |
| CLF | Current Limiting Fuse |
| CLG | Ceiling Level |
| CLO | Constant Light Output (lighting control) |
| CLTD | Cooling Load Temperature Difference |
| CM | Ceiling Mounted |
| CML | Current Mean Life (asset lifecycle) |
| CMMS | Computerised Maintenance Management System |
| CMRR | Common Mode Rejection Ratio |
| CNE | combined neutral and earth |
| CO | Carbon Monoxide |
| CO2 | Carbon Dioxide (greenhouse gas / fire suppression) |
| CO2e | Carbon Dioxide Equivalent |
| COBie | Construction Operations Building Information Exchange |
| COD | Chemical Oxygen Demand |
| CoL | City of London |
| COM | Common |
| Comms | Communications cabling for telecommunications |
| Cond | Condensate pipework (water liberated from air) |
| COP | Coefficient of Performance (heat pump efficiency ratio) |
| COS | Cosine |
| cos 0 | power factor (sinusoidal systems) |
| cos ϕ | power factor, i.e. kW input / kVA input |
| COSHH | Control of Substances Hazardous to Health |
| CP | Call Point (fire alarm) |
| CPAP | Continuous Positive Airway Pressure |
| CPC | circuit protective conductor |
| CPMS | Chargepoint Management System |
| CPO | Chargepoint operator |
| CPR | Construction Products Regulation |
| CPS | Control & protective switching device |
| CPT | Control Power Transformer |
| CPU | Central Processing Unit |
| CPVC | Chlorinated Polyvinyl Chloride pipe |
| CR | Crash Call (nurse call system) |
| CR-C | Card Reader Type C - Commercial Access |
| CR-M | Card Reader Type M - Maintenance Access |
| CR-R | Card Reader Type R - Residential Lift/Stair Core Access |
| CR-RC | Card Reader Type RC - Refuse Commercial Access |
| CR-RR | Card Reader Type RR - Residential Refuse Access |
| CRI | Colour Rendering Index |
| Cs | rating factor for soil thermal resistivity |
| CSA | Cross-Sectional Area |
| CSD | Call System Display unit |
| CSI | Call System Interface |
| CSR | Call System Relay unit |
| Ct | correction factor for the conductor operating temperature |
| CU | Consumer Unit, also known as a fuse box or distribution board. |
| CUSUM | Cumulative Sum (energy management technique) |
| CV | Mounted in Ceiling Void |
| CVT | Constant Voltage Transformer |
| CWBS | Cold Water Booster Set. Packaged pump set (typically duty/standby with controls and vessels) used to boost and maintain domestic cold water pressure to outlets across the building |
| CWDS | Cold Water Distribution Service |
| CWF | Condenser Water Flow pipework |
| CWR | Condenser Water Return pipework |
| CWS | Cold Water Storage cistern or system |
| CWST | Cold Water Storage Tank |
| CY | Screened Flexible Cable (copper braid) |
| DA | Discharge Air ductwork (equipment to atmosphere) |
| DAC | Digital to Analog Converter |
| DADO | 2-Compartment White PVC DADO Trunking |
| DAI | Accessible Toilet Alarm Interface Unit (loop powered) |
| DALI | Digital Addressable Lighting Interface protocol |
| DALI-2 | Digital Addressable Lighting Interface version 2 |
| DAS | Distributed Antenna System. In-building wireless system that distributes mobile radio signal coverage through a network of antennas, cabling and head-end equipment. |
| DB | Distribution Board, a component of an electrical system that distributes electricity to various circuits. |
| DBL | Double (faceplate/backbox size) |
| DBT | Dry Bulb Temperature |
| 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 |
| DCLG | Dept. for Communities and Local Government |
| DCWS | Domestic Cold Water Services. Potable cold water distribution system within the building, including storage tanks, booster sets, and pipework to outlets. |
| DDA | Disability Discrimination Act |
| DDC | Direct Digital Control |
| DEA | Domestic Energy Assessor |
| DEC | Display Energy Certificate |
| DECC | Department of Energy and Climate Change (defunct) |
| DECT | Digital European Cordless Telecommunications |
| DER | Distributed Energy Resources |
| DF | Daylight Factor |
| DG | Diesel Generator |
| DGNB | Deutsche Gesellschaft für Nachhaltiges Bauen (German sustainability standard) |
| DH | Door Hold Open Device |
| DHO | Door Hold Open |
| DHW | Domestic Hot Water. Heated potable water for domestic use. |
| DHW_F | Domestic Hot Water Flow pipework |
| DHW_R | Domestic Hot Water Return pipework |
| DHWS | Domestic Hot Water System |
| DiaLux | Lighting simulation software (DIALux) |
| DICL | Ductile Iron, Cement Lined (pipe) |
| DM | Duty Manager |
| DMX | Digital Multiplex lighting control protocol |
| DN | Nominal Diameter (pipe sizing designation) |
| DNO | Distribution Network Operator |
| DOAS | Dedicated Outdoor Air System |
| DoH | Department of Health |
| DOL | Direct On Line |
| DP | Double Pole |
| DPC | Damp Proof Course |
| DPM | Damp Proof Membrane |
| DPQ | Distribution Power Quality |
| DPS | Dynamic Purchasing System |
| DR | Door Release |
| DRA | Disabled Refuge Alarms |
| DRM | Demand Response Mode |
| DRP | Disabled Refuge Point (also commonly referred to as Refuge Point/Refuge Communication Point). A designated place of relative safety for someone who may not be able to use stairs immediately during an evacuation, typically provided with two-way emergency communication back to the control point (often via an EVC Type B outstation). |
| DS-C | Intercom Door Station - Commercial Access |
| DS-RMP | Intercom Door Station - Residential Maintenance Postal Access |
| DS-RP | Intercom Door Station - Residential Postal Access |
| DSM | Dynamic Simulation Modelling |
| DSO | Distribution System Operator |
| DST | Deep Seal Trap |
| DSY | Design Summer Year (weather data) |
| DTA | Disabled Toilet Alarm |
| DTD | Design Temperature Difference |
| DU | Discharge Unit |
| DVR | Dynamic Voltage Restorer |
| DW | Dish Washer (electrical supply) |
| DWF | Dry Weather Flow |
| DXCU | DX Cooling Unit |
| DZR | Dezincification-Resistant (brass fitting) |
| e.m.f. | electro-motive force |
| EA | Extract Air ductwork (from space to AHU). Synonym: Return Air |
| EAF | Exhaust Air Fan |
| EAP | Evacuation Alert Panel |
| EB | Equipment Branch |
| EBB | Equipotential Earth Bonding Bar |
| EC | Electrical Code or Electrical Contractor |
| ECA | Electrical Contractors Association |
| ECI | European Copper Institute |
| ECP | Emergency Lighting Control Panel |
| ECV | Emergency Voice Communication |
| EDB | Emergency Distribution Board |
| EDM | Energy Data Management |
| 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. |
| EE | Electrical Engineering |
| EEBAD | earthed equipotential bonding & automatic disconnection |
| EEMS | Electrical-Energy Management System |
| EEPROM | Electrically Erasable Programmable Read Only Memory |
| EER | Energy Efficiency Ratio |
| EF | Extract Fan or Exhaust Fan |
| EFD | External Fixed Dome CCTV Camera |
| EFFD | External Fully Functional Dome CCTV Camera |
| EH | Extract Hood (electrical supply) |
| EH40 | HSE Occupational Exposure Limits document (EH40) |
| EHSRs | Essential Health and Safety Requirements (lifts directive) |
| EIA | Environmental Impact Assessment |
| EIA/TIA | Electronic Industries Alliance / Telecommunications Industry Association |
| EIC | Electrical Installation Certificate, a document confirming the safe installation of electrical work. |
| EICR | Electrical Installation Condition Report |
| EIR | Employer's Information Requirements (BIM) |
| ELCB | Earth Leakage Circuit Breaker |
| ELF | Extremely Low Frequency (electromagnetic) |
| ELV | Extra Low Voltage, typically voltages below 50V AC or 120V DC. |
| EM | Emergency |
| Emax | Maximum illuminance |
| EMC | Electromagnetic compatibility |
| EMF | Electromotive Force |
| EMG LTG | Emergency Lighting |
| EMI | Electromagnetic interference |
| Emin | Minimum illuminance |
| EMS | Energy Management System |
| eMSP | e-Mobility Service Provider |
| EMT | Electrical Metallic Tubing |
| EN | European Standard (Euronorm) |
| ENA | Energy Networks Association (UK) |
| EOL | End Of Line unit |
| EP | Emergency Power |
| EP-CCO-CPB | Emergency Pull, Reset, Call Code Orange, Call Pendant Blue |
| EP-CCO-CPB-LTG | Emergency Pull, Reset, Call Code Orange, Call Pendant Blue and Lighting Control |
| EPBD | Energy Performance of Buildings Directive |
| EPC | Energy Performance Certificate |
| EPNC | Twin Plate Emergency Pull and Nurse Call |
| EPO | Emergency Power Off (Button or Switch) |
| EPR | Single Emergency Pull and Reset or Earth Potential Rise |
| EPRI | Electric Power Research Institute |
| ERV | Energy Recovery Ventilator |
| ES | edison screw |
| ESCO | Energy Service Company |
| ESE | Early Streamer Emission |
| ESFR | Early Suppression Fast Response (sprinkler) |
| ESG | Environmental, Social and Governance |
| ESP | Emergency Standby Power Identification Panel |
| ESSS | Electrical source for safety services |
| ETA | Event Tree Analysis (fire/risk assessment) |
| ETD | Estimated Time to Destination (lift) |
| EUFH | Electric Under Floor Heating |
| EUI | Energy Use Intensity |
| EV | Electric vehicle |
| EVC | Emergency Voice Communication system |
| EVCA | Emergency Voice Communication Outstation (Type A). A telephone-style emergency communication point (fire telephone) connected to the EVCS, typically for fire service / trained staff use. |
| EVCB | Emergency Voice Communication Outstation (Type B). A hands-free emergency communication point (typically a refuge intercom) with a call button plus microphone/loudspeaker, connected to the EVCS (Emergency Voice Communication System). Commonly installed at refuge points, lobbies, stairs, etc. |
| EVCL | Emergency Voice Communication Loud speaker |
| EVCP | Emergency Voice Communication Panel |
| EVCRP | Emergency Voice Communication Repeater Panel |
| EVCS | Emergency Voice Communication System |
| EVI | Electric vehicle infrastructure |
| EVO | Efficiency Evaluation Organization |
| EVSE | Electric vehicle supply equipment |
| EWC | Electric Water Cooler |
| EWEA | European Wind Energy Association |
| EWM | Escalator and Moving Walks |
| EX | Existing Fire Alarm Device |
| EXT | External |
| F | Farads |
| F-gG | Fuse type gG |
| F-gM | Fuse type gM |
| FA | Fire Alarm |
| FAA | Fire Alarm Annunciator |
| FAC | Free Available Chlorine |
| FACTS | Flexible AC Transmission Systems |
| FADP | Fire Alarm Display Panel (loop powered) |
| FAI | Fire Alarm Interface |
| FAP | Fire Alarm Panel |
| FARP | Fire Alarm Repeater Panel |
| FAS | Fire Alarm System |
| FAT | Factory Acceptance Testing |
| FB | Floor Box |
| FC | Fire Curtain |
| FCU | Fused Connection Unit, a type of electrical fitting containing a fuse for circuit protection. |
| FDAS | Fire Detection and Alarm System |
| FDB | Fuse Distribution Board |
| FDS | Fire Detection System |
| FED | Fractional Effective Dose (toxicity in fire) |
| FELV | Functional extra-low voltage |
| FF&E | Furniture, Fixtures and Equipment |
| FFFP | Film-Forming Fluoroprotein Foam |
| FFL | Finished Floor Level |
| FFT | smoothing, classification, statistics |
| FG | Floor Gully |
| FGL | Finished Ground Level |
| FHA | Fire Hazard Analysis |
| FHR | Fire Hose Reel |
| FIA | Fire Industry Association |
| FiDR | Fire Fighting Dry Riser (normally without water) |
| FIELDBUS | Field Bus |
| FiF | Fire Fighting Foam system |
| FiGS | Fire Gaseous Suppression system |
| FIP | Fire Indicator Panel |
| FiSp_DP | Fire Sprinkler Dry Pipe system |
| FiSp_M | Fire Sprinkler Main pipework |
| FiSp_PA | Fire Sprinkler Pre-Action system |
| FiSp_WM | Fire Sprinkler Water Mist system |
| FiSp_WP | Fire Sprinkler Wet Pipe system |
| FIT | Feed-in Tariff (renewable energy payment) |
| FiWR | Fire Fighting Wet Riser (normally with water) |
| FLA | Full Load Amps & FLC= Full Load Current - They basically mean the same thing. |
| FLC | full load current |
| FLED | Fuel Load Energy Density |
| FM | Facilities Manager |
| FMC | Flexible Metal Conduit |
| FMEA | Failure Mode and Effects Analysis |
| FO | Fuel Oil pipework |
| FO_D | Fuel Oil Diesel pipework |
| FOGs | Fats, Oils and Grease (drainage) |
| FOH | Front of House |
| FP | Fluoroprotein foam |
| FR | Fridge (electrical supply) |
| FRA | Fire Risk Assessment |
| FRNC | Flame Retardant Non-Corrosive |
| FS | Flow Switch |
| FSE | Fire Safety Engineering |
| FTA | Fault Tree Analysis |
| FTP | Fire Test Performance |
| FW | Foul Water |
| FWD | Food Waste Disposer |
| FWS | Foul Water System |
| FZ | Freezer (electrical supply) |
| G | Ground |
| G98 | Engineering Recommendation G98 (micro-generation grid connection) |
| G99 | Engineering Recommendation G99 (generation grid connection) |
| GAP | Gas Alarm Panel |
| GCV | Gross Calorific Value |
| GdWS | Ground Water Source pipework system |
| GEA | Gross External Area |
| GFP | Residual Sensing ground fault protection[1] (Sensitivity 20% -100% circuit breaker rating) |
| GHG | Greenhouse Gas |
| GHGI | Greenhouse Gas Intensity |
| GHP | Gas Heat Pump |
| GHz | gigahertz (1 GHz = 1,000,000,000 Hz) |
| GI | Galvanised Iron |
| GIA | Gross Internal Area |
| GIS | Gas Insulated Switchgear |
| GMT | Greenwich Mean Time |
| GN | guidance note |
| GND | Ground |
| GNYE | Green-and-yellow (conductor colour) |
| GPI | General Purpose Interface |
| GPR | Ground Potential Rise |
| GRESB | Global Real Estate Sustainability Benchmark |
| GRMC | Galvanized Rigid Metal Conduit |
| GRP | Glass Reinforced Plastic |
| Gs | Generator Set |
| GSHP | Ground Source Heat Pump |
| GW | Grey Water (water reused in secondary function) |
| GWh | Gigawatt Hour |
| GWP | Grey Water Pipe (to treatment or storage) |
| H | Digital Addressable Heat Sensor (fire detector) |
| h | Net Head, also related to hydro power generation. |
| H2S | Hydrogen Sulphide |
| HAZOPS | Hazard and Operability Study |
| HB | Hob (electrical supply) |
| HBC | high breaking capacity (fuse) |
| HC | Hose union backflow preventer type HC |
| HCA | Hall Call Allocation (lift) |
| HCFCs | Hydrochlorofluorocarbons (refrigerants) |
| HCN | Hydrogen Cyanide |
| HD | Harmonization Document (CENELEC) |
| HD | Hand Dryer |
| HDC | High Density Copper |
| HDMI | High-Definition Multimedia Interface socket |
| HDU | High-Dependency Unit |
| HDV | Header vent pipe (plumbing drawing symbol) |
| HEPA | High-Efficiency Particulate Air filter |
| HF | High frequency |
| HGV | Heavy goods vehicle |
| HHD | Half-Hourly Data (energy metering) |
| HIU | Heat Interface Unit. Packaged unit that transfers heat from a communal/district heating network into an individual dwelling’s heating and DHW circuits, typically via plate heat exchangers and control valves. |
| HIVE | Hive smart thermostat (UK). Branded smart heating control system (thermostat, receiver and hub) that allows app‑based scheduling and remote control of a boiler or heat pump, often integrated with wider smart‑home platforms. |
| HL | High Level |
| HMI | Human Machine Interface |
| HOA | Hand-Off-Automatic Switch |
| HPPE | High Performance Polyethylene pipe |
| HQE | Haute Qualité Environnementale |
| HRC | high rupturing capacity (fuse) |
| HRR | Heat Release Rate (fire engineering) |
| HRV | Heat Recovery Ventilator |
| HSE | Health and Safety Executive |
| HSWA | Health and Safety at Work Act |
| HTHW | High Temperature Hot Water (above 120°C) |
| HTHWS | High Temperature Hot Water System |
| HTM | Health Technical Memorandum (NHS technical guidance) |
| HTML | HyperText Markup Language |
| HTR | Heater |
| HTW | Heat Transfer Water pipework |
| HV | High Voltage power cables (exceeding LV) |
| HVAC | Heating, Ventilation, Air Conditioning |
| HWF | Hot Water Flow pipe |
| HWR | Hot Water Return pipe |
| HWS | Hot Water Services (synonym for DHW) |
| HWST | Hot Water Storage Tank |
| Hz | Hertz, the unit of frequency, representing cycles per second. |
| HZD | Hazard |
| 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 |
| IAP | Intruder Alarm Panel |
| IAQ | Indoor Air Quality |
| 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. |
| ICP | Independent Connection Provider |
| 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. |
| ICT | Information and Communications Technology |
| 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 |
| IDA | Indoor Air (CIBSE/EN 13779 air quality classification) |
| IDC | Insulation Displacement Contact |
| 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 |
| IDNO | Independent Distribution Network Operator |
| IE5 | Motor efficiency class IE5 |
| IEE | Institution of Electrical Engineers |
| IEQ | Indoor Environmental Quality |
| IET | Institution of Engineering and Technology |
| IFAWT | Interfloor Average Waiting Time (lift) |
| IFC | Industry Foundation Classes (open BIM file format) |
| IFD | Internal Fixed Dome CCTV Camera |
| IFFD | Internal Fully Functional Dome CCTV Camera |
| Ifi | follow-on current interrupt rating of SPD |
| IFW | Informative Fire Warning |
| IG | Isolated Ground |
| IGBT | Insulated Gate Bipolar Transistor |
| IGEM | Institution of Gas Engineers and Managers |
| IH | Interharmonic |
| Ik | rated short-time withstand current (r.m.s.) of equipment |
| IL | Invert Level |
| 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 |
| Imp | Maximum Power Current (PV) |
| IMPR | electronic device |
| IMS | Information Management System |
| In | rated current or current-setting of protective device |
| INAWT | Interfloor Average Passenger Waiting Time (lift) |
| INT | Interlock |
| INU | Insulation neutral unit |
| IoT | Internet of Things |
| Ip | rated peak withstand current of equipment |
| IP (code) | Ingress-Protection code to BS EN 60529 |
| IP-APP1 | Nurse Call Application Station |
| IP-TSNS | Touch Screen Nurse Station (Nurse Call) |
| Ipf | prospective fault current at a point in the installation |
| IPPC | Integrated Pollution Prevention and Control |
| IPS | Intelligent Power System |
| Ir | Overload current setting (long-time trip threshold) |
| Irm | motor overload setting |
| IRS | Integrated Reception System |
| Is | Isolator base (fire detector) |
| Isc (STC) | short-circuit current of a PV module/string/array under standard test conditions |
| Isccr | short-circuit current rating of SPD + OCPD combination |
| ISDN | Integrated Services Digital Network |
| ISO | International Organisation for Standardisation |
| IST | Integrated System Test |
| It | current-carrying capacity under installation conditions |
| IT system | Unearthed LV supply system |
| ITIC | Information Technology Industry Council |
| ITT | Invitation to Tender |
| ITU | International Telecommunication Union |
| IVC | In-Vessel Composting |
| Iz | current-carrying capacity of a cable for continuous service |
| IΔn | rated residual operating current of an RCD |
| JB | Junction Box |
| JCT | Joint Contracts Tribunal (UK construction contract) |
| JIT | Just in Time |
| k | kilo - one thousand times |
| K-U | Key Lock Access - IDNO/DNO only |
| 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) |
| KEF | Kitchen Extract Fan |
| kHz | kilohertz (1 kHz = 1000 Hz) |
| KL | Kitchen Cabinet Lighting |
| kPa | Kilopascal (1000 Pascals) |
| KPI | Key Performance Indicator |
| KS | Knowledge Series (CIBSE publication) |
| kV | kilovolts (1 kV = 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. |
| KVAR | Kilovolt-Amperes Reactive |
| kW | Kilowatt, a unit of power equal to 1000 watts. |
| kWh | Kilowatt-hour (unit of energy) |
| kWp | Kilowatt peak (PV system capacity) |
| kΩ | Kilo-ohm (1 kΩ = 1000 Ω) |
| LABC | Local Authority Building Control |
| LAN | Local Area Network |
| LAT | Local Apparent Time (solar) |
| LC | Local Control |
| LCA | Life Cycle Assessment |
| LCC | Life Cycle Cost |
| LCM | Lighting Control Module |
| LCP | Lighting Control Panel |
| LDB | Lighting Distribution Board |
| LDR | Light Dependent Resistor |
| LED | Light-emitting diode |
| LEED | Leadership in Energy and Environmental Design |
| LENI | Lighting Energy Numeric Indicator |
| LEV | Local Exhaust Ventilation |
| LEVI | Local Electric Vehicle Infrastructure Fund |
| LFMC | Liquid Tight Flexible Metal Conduit |
| LFSM-O | Limited Frequency Sensitive Mode - Overfrequency |
| LIMS | Lighting Management System |
| LL | Low Level |
| lm | Lumen (unit of luminous flux) |
| LMTD | Logarithmic Mean Temperature Difference |
| LNG | Liquefied Natural Gas |
| LOD | Level of Development (BIM maturity) |
| LOI | Level of Information (BIM) |
| LOLER | Lifting Operations and Lifting Equipment Regulations |
| LOM | Loss of Mains detection |
| LOR | Light Output Ratio |
| LPCB | Loss Prevention Certification Board |
| LPG | Liquefied Petroleum Gas |
| LPHW | Low Pressure Hot Water (synonym for LTHW) |
| LPL | Lightning Protection Level |
| LPQI | Leonardo Power Quality Initiative |
| LPS | Loss Prevention Standard |
| LRA | Locked Rotor Amp |
| LSC | Luminaire supporting coupler |
| LSF | Low Smoke and Fume cable sheathing |
| LSFNH | Low Smoke Free of Halogen (LSFNH cable designation) |
| LSFW | Low Speed Flywheel |
| LSHF | Low Smoke Halogen Free |
| LSNG | Low Smoke Non-Gelatinised (LSNG cable designation) |
| LSNH | Low Smoke Zero Halogen (LSNH cable designation) |
| LSOH | Low Smoke Zero Halogen |
| LSZH | Low Smoke Zero Halogen cable sheathing |
| 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 |
| LTHW | Low Temperature Hot Water. Heating water circuit, typically serving radiators, underfloor heating, or AHU heating coils. |
| LTHW_F | Low Temperature Hot Water Flow pipework |
| LTHW_R | Low Temperature Hot Water Return pipework |
| LTHWP | Low Temperature Hot Water Pump. |
| LTHWS | Low Temperature Hot Water System |
| LUL | London Underground Limited |
| lux | Unit of illuminance (lumens per square metre) |
| LV | Low voltage (50 V – 1 000 V ac) |
| LW | Sound power level |
| lx | Lux (unit of illuminance) |
| LZC | Low or Zero Carbon energy source |
| M | Multifunction Detector or Motor (context dependent) |
| m | metre |
| M&E | Mechanical and Electrical engineering |
| m.i. | mineral-insulated |
| mA | Milliampere, one-thousandth of an ampere. |
| MaaS | Mobility as a Service |
| MAN | Manual |
| MAWP | Maximum Allowable Working Pressure |
| MAX | UOC = Open Circuit Voltage |
| MBR | Membrane Bioreactor |
| MBus | Meter-Bus (energy metering communication protocol) |
| MC | Metal Clad Cable |
| MCA | Min. Circuit Amps (Amp) |
| MCB | Miniature Circuit Breaker |
| MCC | Motor Control Center |
| MCCB | Moulded Case Circuit Breaker |
| MCCP | Motor Control Centre Panel |
| MCH | Mechanical (pump system reference) |
| MCL | Metalclad |
| MCP | Motor Circuit Protection |
| MCS | Microgeneration Certification Scheme |
| MCW | Mains Cold Water pipework (direct from water main) |
| MCWS | Main Cold Water Service |
| MD | maximum demand |
| MDB | Main Distribution Board |
| MDPE | Medium Density Polyethylene pipe |
| MEES | Minimum Energy Efficiency Standard |
| MEN | Multiple Earthed Neutral |
| MEng | Master of Engineering |
| MEP | Mechanical, Electrical and Plumbing engineering |
| MEPH | Mechanical, Electrical and Public Health (Services) |
| MEPS | Minimum Energy Performance Standards |
| MER | Main Equipment Room (IT). Primary IT/telecoms equipment room (main comms hub) housing core network equipment (racks, switches/routers, patch panels, main terminations, etc.), often with associated UPS/cooling provisions as applicable. |
| MESH-BN | Meshed bonding network |
| MET | Main Earthing Terminal |
| Mf | Multifunction (fire detector) |
| MFH | Maximum Fire Heat Release Rate |
| MG | Medical Gas Services pipework |
| MG_AGS | Medical Gas Anaesthetic Gas Scavenging pipework |
| MG_CO2 | Medical Gas carbon dioxide supply pipework |
| MG_MA | Medical Air supply pipework |
| MG_MV | Medical Vacuum pipework |
| MG_N2 | Medical Nitrogen supply pipework |
| MG_N2O | Medical Nitrous Oxide supply pipework |
| MG_O2 | Medical Oxygen supply pipework |
| MGP | Medical Gas Alarm Panel |
| MGPS | Medical Gas Pipeline System |
| mH | millihenry (1000 mH = 1 H) |
| MHz | megahertz (1 MHz = 1,000,000 Hz) |
| MI | Mineral Insulated |
| MIC | Microbially Influenced Corrosion |
| MICC | Mineral Insulated Copper Clad cable |
| MICS | Mineral Insulated Cables |
| MIDAWT | Mid-Day Average Waiting Time (lift) |
| MIDP | Master Information Delivery Plan |
| ML | Mid Level (mounting position) |
| MLO | Main Lugs Only |
| MLVS | Prisma P |
| MODBUS | Serial Communication Protocol |
| MOP | Max Overcurrent Protection (Amp) |
| MPAN | Meter Point Administration Number |
| MPHW | Medium Pressure Hot Water |
| MPP | Maximum Power Point |
| MRCD | Modular residual-current device |
| MRL | Machine Room-Less (lift type) |
| MRSA | Methicillin-Resistant Staphylococcus Aureus |
| MRT | Mean Radiant Temperature |
| mS | Millisiemen (1000 mS = 1 S) |
| MSB | Main Switchboard |
| MSC | Max Starting Current (Amp) |
| MSFD | Motorised Fire Smoke Damper |
| MSW | Municipal Solid Waste |
| MTBF | Mean Time Between Failure |
| MTHW | Medium Temperature Hot Water (90–120°C) |
| MTHWS | Medium Temperature Hot Water System |
| MTS | Manual Transfer Switch |
| MTTR | Mean Time To Repair |
| mV | millivolts (1000 mV = 1 V) |
| MVA | Megavolt-Ampere |
| MVHR | Mechanical Ventilation with Heat Recovery. Centralised fan and ductwork system that continuously supplies filtered fresh air and extracts stale air, using a heat exchanger to recover heat from exhaust air to pre‑warm the incoming air. |
| mW | milliwatt (1000 mW = 1 W) |
| MWh | Megawatt-hour (1000 kWh) |
| MΩ | Megaohm, one million ohms. |
| N/C | Normally Closed |
| N/O | Normally Open |
| N2O | Nitrous Oxide |
| NABERS | National Australian Built Environment Rating System |
| NAPIT | National Association of Professional Inspectors and Testers |
| NBS | National Building Specification |
| NC | Normally Closed |
| NCE | Nurse Call Emergency Indicator Panel |
| NCM | National Calculation Methodology (UK energy) |
| NCP | Nurse Call Central Panel |
| NCRP | Nurse Call Repeater Panel |
| NCV | Net Calorific Value |
| NDEAP | Non-Domestic Energy Assessor Qualification |
| NEC | National Electrical Code |
| NEC4 | New Engineering Contract 4th Edition |
| NEVIS | National EV Insight & Support |
| nF | nanofarads (1,000,000,000 nF = 1 F) |
| NFPA | National Fire Protection Association |
| NG | Natural Gas pipework (for combustion) |
| NI | Nurse Intercom |
| NIA | Net Internal Area |
| NiCad | Nickel-Cadmium (battery) |
| NICEIC | National Inspection Council for Electrical Installation Contracting |
| NJUG | National Joint Utilities Group |
| NL | Night Light |
| NLA | Net Lettable Area |
| NMOT | Nominal Module Operating Temperature |
| NO | Normally Open or Number |
| NPSH | Net Positive Suction Head |
| NPSHR | Net Positive Suction Head Required |
| NPV | Net Present Value |
| NR | Noise Rating curve (room acoustics) |
| NRSWA | New Roads and Street Works Act 1991 |
| NRV | Non-Return Valve |
| NTP | Normal Temperature and Pressure |
| NTS | Not To Scale |
| NTU | Nephelometric Turbidity Unit |
| nU | Rack unit (19-inch equipment rack height unit) |
| NWF | Navisworks File |
| O | Optical (fire detector type) |
| O&M | Operation and Maintenance documentation |
| OC Device | Over-current device |
| OCPD | Over-current protective device |
| OCPI | Open Charge Point Interface |
| OCPP | Open Charge Point Protocol |
| ODA | Outdoor Design Air (CIBSE outdoor air quality class) |
| ODL | Overdoor Lamp |
| ODLT | Overdoor Lamp with Tone Sounder |
| ODP | Ozone Depletion Potential |
| OEM | Original Equipment Manufacturer |
| OFGEM | Office of Gas and Electricity Markets |
| OFTEC | Oil Firing Technical Association |
| OIR | Organization Information Requirements |
| OPC | OLE for Process Control |
| OPEX | Operational Expenditure |
| ORC | Organic Rankine Cycle |
| OSG | On Site Guide (IET) |
| OT | Operative Temperature |
| OTA | Over-The-Air (firmware update) |
| OTTV | Overall Thermal Transfer Value |
| OV | Oven (electrical supply) |
| OZEV | Office for Zero Emission Vehicles |
| P | Pole |
| P&ID | Piping and Instrumentation Diagram |
| P+E | Poles and Earth (connector) |
| p.d. | potential difference |
| p.v.c. | poly-vinyl chloride |
| Pa | Pascal (unit of pressure) |
| PAC | Public Address Control |
| PAHs | Polycyclic Aromatic Hydrocarbons |
| PAS | Publicly Available Specification (BSI) |
| PAS 1899 | Publicly Available Specification for EV accessible charging |
| PAU | Primary Air Unit |
| PAVA | Public Address / Voice Alarm Panel |
| PB | Push Button or Panic Button or Pull Box |
| PC | Personal Computer |
| PCB | PolyChlorinated Biphenyl |
| PCC | Point of Common Coupling |
| PCG | Project Control Group |
| PCR | Access Control Proximity Card Reader / Swipe Card |
| PD | Mini DALI Multi-function Presence/Absence Detector |
| PDB | Power Distribution Board |
| Portable Document Format | |
| PDM | Predictive/Condition-based Maintenance |
| PDT | Power Demand Tariff |
| PDU | Power Distribution Unit (data centre) |
| PE | Protective conductor |
| PEC | Z sup |
| PEEPs | Personal Emergency Evacuation Plans |
| 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 |
| PEP | Project Execution Plan |
| PES | Primary Electrical Supply |
| PESSRAL | Programmable Electronic Systems in Safety Related Applications for Lifts |
| PEX | Cross-linked Polyethylene pipe |
| pF | picofarads (1,000,000,000,000 pF = 1 F) |
| PFC | Power Factor Correction |
| PFP | Passive Fire Protection |
| PG | Plantroom Gully |
| PH | Panel Heater |
| PH120 | Fire Performance 120 minutes (cable rating) |
| PH60 | Fire Performance 60 minutes (cable rating) |
| PHE | Plate Heat Exchanger |
| PHEV | Plug-in hybrid electric vehicle |
| PHPP | Passive House Planning Package (energy design tool) |
| PI | Proportional plus Integral (control) |
| PICV | Pressure Independent Control Valve |
| PID | Proportional Integral Derivative |
| PILC | Paper Insulated Lead Covered (cable) |
| PIM | Project Information Model |
| PIR | passive infra-red detector |
| PiV | Plug-in vehicle |
| PLC | Programmable Logic Controller |
| PLT | Long Term Flicker Severity |
| PM | Project Manager |
| PM10 | Particulate matter ≤10 µm diameter |
| Pmax | Maximum Power (PV module) |
| PMD | Power Meters |
| PME | Protective multiple earthing (UK TN-C-S supply) |
| PMS | Power Monitoring System |
| PMSM | Permanent Magnet Synchronous Motor (lift) |
| PMV | Predicted Mean Vote (thermal comfort index) |
| Pn | nominal power (in kW) |
| PNL | Panel |
| PoE | Power over Ethernet |
| PPD | Predicted Percentage Dissatisfied (thermal comfort) |
| PPE | Personal protective equipment |
| ppm | Parts per million (concentration unit) |
| PQ | Power Quality |
| PQI | Power Quality Instruments |
| PQM | Power Quality Management |
| PQQ | Pre-Qualification Questionnaire |
| PROFIBUS | Process Field Bus |
| PRV | Pressure Reducing Valve |
| PS | Push Switch |
| PS-ACR | Power Sum ACR |
| PS-NEXT | Power Sum NEXT (near-end crosstalk measurement) |
| PSC | prospective short-circuit current |
| PSCC | Prospective Short-Circuit Current |
| PSOP | Pool Safety Operating Procedure |
| PST | Short Term Flicker Severity |
| PSU | Power Supply Unit |
| PSV | Pressure Safety Valve (pressure relief) |
| PT | Potential Transformer |
| PTE | Push To Exit |
| PTZ | Pan Tilt Zoom (camera) |
| PUE | Power Usage Effectiveness (data centres) |
| PUWER | Provision and Use of Work Equipment Regulations |
| PV | Photovoltaic (solar) |
| PVC | Polyvinyl Chloride |
| PWD | Person with Disability |
| PWDHD | Partial Weighted Harmonic Distortion |
| PWLB | Public Works Loan Board |
| PWM | Pulse Width Modulation |
| PWR | Power |
| Q (SPD) | total charge (coulombs) associated with SPD impulse test |
| QA | Quality Assurance |
| QDP | Quadruple (faceplate/backbox size) |
| QDR | Qualitative Design Review (fire) |
| QRA | Quantified Risk Assessment |
| QS | Quantity Surveyor |
| 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 |
| RAD | Radiator |
| RAF | Return Air Fan |
| RAID | Redundant Array of Independent Disks |
| RAM | Random Access Memory |
| RC | Room Criterion (noise) |
| RCBO | RCD with integral over-current protection |
| RCCB | Residual Current Circuit Breaker |
| RCD | Residual-current device (RCCB or RCBO) |
| RCM | Reliability Centred Maintenance |
| RCW | Recycled Cold Water pipework |
| RE | Resident Engineer |
| REC | Recommendation (IET) |
| REF | Restricted Earth-Fault detection |
| REQ | Required |
| RES | Renewable Energy Source |
| Rf | Refrigerant pipework system |
| Rf_G | Refrigerant Gas pipework |
| Rf_L | Refrigerant Liquid pipework |
| Rf_VF | Variable Refrigerant Flow System pipework |
| RFI | Request for Information |
| RH | Relative Humidity |
| RHI | Renewable Heat Incentive |
| RHS | Rectangular Hollow Section (structural steel) |
| RI | Remote Indicator |
| RIBA | Royal Institute of British Architects |
| RICS | Royal Institution of Chartered Surveyors |
| RJ45 | Registered Jack 45 (8-pin modular connector) |
| RLA | Rated Load Amps (Amp) |
| RMC | Rigid Metal Conduit |
| RMS | Root Mean Squared |
| RMU | Ring Main Unit |
| RNC | Rigid Non-Metallic Conduit |
| RO | Reverse Osmosis |
| RoCoF | Rate of Change of Frequency |
| RoHS | Restriction of Hazardous Substances |
| ROM | Read Only Memory |
| Rp | prospective rise of earth potential (EPR) |
| rpm | Revolutions per minute |
| RPZ | Reduced Pressure Zone (backflow prevention device) |
| RSET | Required Safe Egress Time |
| RTE | Request To Exit (push button) |
| RTI | Response Time Index (sprinkler) |
| RTT | Round Trip Time (lift performance) |
| RTU | Remote Terminal Unit |
| RVC | Roof Ventilation Control |
| RWOF | Rainwater Overflow |
| RWP | Rain Water Pipe (above ground surface water removal) |
| RWWP | Rainwater Warning Pipe |
| S | Substation or Smoke Detector (context dependent) |
| s | cross-sectional area of a conductor (mm²) |
| SA | Staff Assist (nurse call) or Supply Air ductwork |
| SAF | Supply Air Fan |
| SAP | Standard Assessment Procedure (dwelling energy rating) |
| SAT | Site Acceptance Testing |
| SB | Slab Box |
| SBEM | Simplified Building Energy Model (non-domestic) |
| SBR | Sequencing Batch Reactor (wastewater) |
| SCADA | Supervisory control and data acquisition |
| SCBU | Special Care Baby Unit |
| SCL | Solar Cooling Load factor |
| SCOP | Seasonal Coefficient of Performance |
| SCP | Surgeon's Control Panel |
| SCPD | ShortCircuit Protective Device |
| SCR | Selective Catalytic Reduction |
| SD | Smoke Damper or Star Delta (motor starter) |
| SDA | Spatial Daylight Autonomy (daylight metric) |
| SDB | Submain Distribution Board |
| SDBA | Standard-Duration Breathing Apparatus |
| SDCP | Smoke Damper Control Panel |
| SDS | Safety Data Sheet |
| SE | Service Entrance |
| SEB | Service End Line Box or Service Electrical Box |
| Sec | Security system cabling and containment |
| SEC(M) | Security Alarm (Intruder Alarm Panel) Main Panel |
| SEC(R) | Security Alarm (Intruder Alarm Panel) Sub Panel |
| SEER | Seasonal Energy Efficiency Ratio |
| SELECT | Scottish Electrical Contractors Association |
| SELV | seperated extra-low voltage |
| SEN | Separate earth and neutral (TN-S) |
| SER | Satellite Equipment Room (IT). Secondary/local IT equipment room supporting a floor/zone, typically providing local network distribution (racks, switches, patch panels) and up-linking back to the MER. |
| SES | Scottish Engineering Services |
| SET | Standard Effective Temperature |
| SF6 | Sulphur Hexafluoride (switchgear insulating gas) |
| SFG20 | Standard Maintenance Specification for Building Services (BESA) |
| SFL | Structural Floor Level |
| SFP | Specific Fan Power (W per l/s) |
| SFPE | Society of Fire Protection Engineers |
| SFS | Soft-starter |
| SGL | Single (faceplate/backbox size) |
| SHEVS | Smoke and Heat Exhaust Ventilation System |
| SHGC | Solar Heat Gain Coefficient |
| SHR | Specular Reflection Factor |
| SHS | Square Hollow Section (structural steel) |
| SHTM | Scottish Health Technical Memorandum |
| SHW | Solar Hot Water primary pipework system |
| SHW_F | Solar Hot Water Flow pipework |
| SHW_R | Solar Hot Water Return pipework |
| SIL | Safety Integrity Level |
| SIS | Solid Insulated Switchgear |
| sk | cross-sectional area of conductor k (parallel runs) |
| SLA | Service Level Agreement |
| SLD | Single Line Diagram |
| SLL | Society of Light and Lighting |
| SLVE | CCTV Slave 15-inch LCD Monitor |
| SMD | Soil Moisture Deficit |
| SMDB | Sub-Main Distribution Board |
| SMES | Superconducting Magnetic Energy Storage |
| SMP | Standard Method and Procedure |
| SMPS | Switched Mode Power Supply |
| So | Sounder base (fire detector) |
| SO2 | Sulphur Dioxide |
| SOC | State of charge |
| SOFC | Solid Oxide Fuel Cell |
| SOG | Soffit of Grid |
| SP | Spare |
| SP&N | Single Pole and Neutral (distribution board type) |
| SPD | Surge protective device |
| SPDT | Single Pole Double Throw |
| SPE | or PEN |
| SPL | Sound Pressure Level |
| SPST | Single Pole Single Throw |
| SRB | Sulphate Reducing Bacteria |
| SRC | System Remote Control |
| SRL | Self Righting Luminaire |
| SROH | Specification for Reinstatement of Openings in Highways |
| SS | Stainless Steel |
| SSAIB | Security Systems and Alarms Inspection Board |
| SSB | Secondary Switchboard |
| SSEN | Scottish and Southern Electricity Networks |
| SSL | Structural Slab Level |
| SSO | Single Switched Socket Outlet |
| SSR | Solid State Relay |
| ST | Shunt Trip |
| STATCOM | Static Synchronous Compensator |
| STC | Standard Test Conditions |
| STLG | Structural Level |
| STP | Standard Temperature and Pressure |
| STS | Static transfer switch |
| SUDS | Sustainable Urban Drainage Systems |
| SV | Safety Valve |
| SVC | Static Var Compensator |
| SVCP | Smoke Vent Control Panel |
| SVHC | Substances of Very High Concern |
| SVP | Soil Vent Pipe (above ground foul water and ventilation) |
| SW | Switch |
| SWA | Steel Wire Armoured cable |
| SWG | Storm Water Gully |
| SWL | Sound Power Level |
| SWMP | Site Waste Management Plan |
| SWP | Soil Waste Pipe |
| SWS | Surface Water Source pipework (thermal energy) |
| SXT | Sextuple (faceplate/backbox size) |
| SY | Screened Flexible Cable (braided) |
| SYM | Symmetrical |
| t | time |
| TAC | Total Available Chlorine |
| TAR | Transmission, Absorption and Reflection (glazing) |
| TBM | Thermal Bridging Multiplier |
| TBS | Temporary Builders Supply |
| TCO | Total cost of ownership |
| TCR | Thyristor Controlled Reactor |
| TCWS | Boosted Cold Water Services |
| TD | To Drain (drainage drawing notation) |
| TDP | Thermal Decomposition Products (fire) |
| TDR | Temperature Difference Ratio |
| TDS | Total Dissolved Solids |
| TEDI | Thermal Energy Demand Intensity |
| TEL | Telecommunications, Telephone |
| TER | Target Emission Rate (Building Regulations Part L) |
| TfGM | Transport for Greater Manchester |
| TfL | Transport for London |
| TFM | Total Facilities Management |
| TH | Trace Heating |
| THD | Total Harmonic Distortion |
| THD(V) | Total Harmonic Distortion (voltage) |
| THDI | Total Harmonic Distortion of Current |
| THDU | Total Harmonic Distortion of Voltage |
| THMs | Trihalomethanes (water treatment byproduct) |
| TIDP | Task Information Delivery Plan |
| TM | Technical Memorandum (CIBSE publication series) |
| TMCB | Thermal Magnetic Circuit Breaker |
| TMO | Traffic Management Order |
| TMV | Thermostatic Mixing Valve |
| 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 |
| TOC | Top of Concrete |
| TOD | Top of Duct |
| TOS | Top of Steel |
| TOV | Temporary over-voltage |
| tp | maximum permitted normal operating conductor temp. (°C) |
| TP&N | Three Pole and Neutral (distribution board type) |
| TPDDI | Twisted Pair Distributed Data Interface |
| TPN | Three Phase and Neutral |
| TR | Towel Rail (electrical supply) |
| tr | Long-time delay setting (overload trip response speed) |
| TrH | Trace Heating |
| TRO | Traffic Regulation Order |
| TRV | Thermostatic Radiator Valve |
| TS | Tap Sensor |
| TSC | Thyristor Switched Capacitor |
| TSO | Transmission System Operator |
| TSRGD | Traffic Signs Regulations and General Directions 2016 |
| TSSO | Twin Switched Socket Outlet |
| TT | LV system with consumer earth electrode, supply earth separate, Terre Terre (Earthed) |
| TTA | Type Tested Assembly |
| TTS | Transmitter Test Station (nurse call system) |
| TUV | Technischer Ueberwachungsverein (German technical inspection association) |
| TVOC | Total Volatile Organic Compounds |
| TX | Transformer |
| U | symbol for voltage (alternative for V) |
| U0 | Voltage to earth of LV system |
| Uac | alternating voltage |
| UB | Universal Beam (structural steel) |
| Uc | continuous operating voltage of SPD mode of protection |
| Udc | direct voltage |
| UDI | Useful Daylight Illuminance |
| Ue | Rated Operational voltage |
| UF | Urea Formaldehyde |
| UFH | Under Floor Heating (electrical) |
| UFHM | Underfloor Heating Manifold (pump supply) |
| UG | Under Ground |
| UGR | Unified Glare Rating (lighting) |
| Ui | Rated Insulation voltage |
| UIE | International Union for Electrotechnology |
| Uimp | Rated impulse withstand voltage |
| UKCA | UK Conformity Assessed |
| UKPN | UK Power Networks |
| UL | Underwriters Laboratory |
| Uo | phase voltage |
| Uo-c | open-circuit voltage of PV string/array |
| Up | SPD rated limiting (protection) voltage |
| UPPHC | Up-Peak Handling Capacity (lift) |
| UPPINT | Up-Peak Interval (lift) |
| UPS | Uninterruptible power supply |
| UPVC | Unplasticized Polyvinyl Chloride |
| US | Underside (drawing notation) |
| USB | Universal Serial Bus power outlet |
| Utν | temporary over-voltage (power-frequency, kV) |
| UV | Ultraviolet (treatment/disinfection) |
| Uw | rated impulse-withstand voltage of equipment insulation |
| V | Volt, the unit of electrical potential or voltage. |
| V2B | Vehicle-to-building |
| V2G | Vehicle-to-grid |
| V2H | Vehicle-to-home |
| V2X | Vehicle-to-everything (bidirectional charging) |
| VA | Volt-Ampere, a unit of apparent power. |
| VAC | Alternating Current Voltage |
| VAD | Visual Alarm Device. A visual warning unit (e.g., strobe) used to provide a fire alarm warning for occupants who may not hear audible alarms. Often used in circulation spaces, and accessible areas depending on the fire strategy and standards. |
| VAV | Variable Air Volume ductwork terminal unit |
| VCB | Vacuum Circuit Breaker |
| VD | Void Detection |
| VDC | Volts, direct current. |
| VDE | Verband Deutscher Elektrotechniker |
| VDU | Visual Display Unit |
| VESDA | Very Early Smoke Detection Apparatus |
| VFD | Variable Frequency Drive |
| VFI | Voltage and Frequency Independent |
| VID | Visual Indicator Device |
| VIE | Vacuum Insulated Evaporator (medical oxygen) |
| VIS | Visual Indicator and Sounder base |
| VLAN | Virtual Local Area Network |
| Vmp | Maximum Power Voltage (PV) |
| VOC | Volatile Organic Compound (indoor air pollutant) |
| VOCs | Volatile Organic Compounds |
| VP | Vent Pipe (ventilation for waste or soil drainage stacks) |
| VPN | Virtual Private Network |
| VRF | Variable Refrigerant Flow multi-split system |
| VRV | Variable Refrigerant Volume |
| VSC | Voltage Source Converter |
| VSD | Variable Speed Drive |
| VSF | Variable Speed Fan |
| VSS | Video Surveillance System recorder |
| VT | Voltage Transformer |
| VVVF | Variable Voltage Variable Frequency (lift drive) |
| W | watt - unit of power |
| WAN | Wide Area Network |
| WAP | Wireless Access Point |
| WB | Wet Bulb (temperature) |
| WBGT | Wet Bulb Globe Temperature (heat stress index) |
| WBT | Wet Bulb Temperature |
| WC | Water Closet (toilet) |
| WD | Waste Disposal (electrical supply) |
| WEEE | Waste Electrical and Electronic Equipment |
| WELL | WELL Building Standard (health and wellness certification) |
| WG | Water Gauge (pressure unit) |
| WH | Water Heater |
| WHA | Water Hammer Arrestor |
| WHB | Wash Hand Basin |
| WHO | World Health Organisation |
| WIP | Work In Progress |
| WL | Wardrobe Integrated Lighting within Joinery |
| WLAN | Wireless Local Area Network |
| WLD | Water Leak Detection System |
| WM | Washing Machine or Water Meter |
| WP | Weatherproof or Waterproof |
| WRAS | Water Regulations Advisory Scheme |
| WS | Water Softener (electrical supply) |
| WSHP | Water Source Heat Pump. Heat pump that exchanges heat with a water loop (rather than outdoor air), providing local heating/cooling depending on system configuration. |
| WUE | Water Usage Effectiveness |
| WVP | Waste Vent Pipe |
| X | reactance |
| XLPE | Cross-Linked Polyethylene |
| XLPE/SWA/LSF | Cross Linked Polyethylene / Steel Wire Armour / Low Smoke Fume |
| Z | Impedance (measured in Ω) |
| Zdb | earth-fault loop impedance at a distribution board |
| Ze | external earth-fault loop impedance (supply) |
| ZEV | Zero emission vehicle |
| ZI | Zone Isolator |
| Zip | Zip Tap |
| Zs | earth-fault loop impedance of a circuit |
| ZT | Zip Tap (boiling water tap supply) |
| 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. |
| ΩT | earthing-system resistance target value |
