Electrical Abbreviations & Glossary
Quick reference for UK electrical terminology, BS 7671 symbols, and trade abbreviations
12 Categories
Circuit Design — Current HierarchyTest & Measurement ParametersProtective DevicesCable Types & ConductorsEarthing SystemsSupply & Three-PhaseCertificates & Building RegsOrganisations & StandardsFire Alarm Categories (BS 5839-1)Emergency Lighting (BS 5266)Installation Reference MethodsHistorical Terminology Changes
Circuit Design — Current Hierarchy
| Abbreviation | Full Term | Note |
|---|---|---|
| Ib | Design Current | Current the circuit is intended to carry in normal service |
| In | Rated Current of Protective Device | Nominal rating — e.g. 32 A for a ring final |
| Iz | Current-Carrying Capacity | Max current the installed cable can safely carry (after correction factors) |
| It | Tabulated Current | Cable capacity from BS 7671 Appendix 4 tables (before corrections) |
| I2 | Operating Current | Current causing the protective device to trip in the required time |
| Ca | Ambient Temperature Factor | Correction for temperatures other than 30 °C |
| Cg | Grouping Factor | Correction when cables are bundled together |
| Ci | Thermal Insulation Factor | Correction for cable enclosed in thermal insulation |
Test & Measurement Parameters
| Abbreviation | Full Term | Note |
|---|---|---|
| Ze | External Earth Fault Loop Impedance | Measured at the origin — includes transformer and DNO cable |
| Zs | Total Earth Fault Loop Impedance | Ze + (R1 + R2) — compared against max Zs tables |
| Zdb | Distribution Board Impedance | Impedance at a sub-distribution board |
| R1 | Line Conductor Resistance | Phase conductor resistance of the circuit |
| R2 | CPC Resistance | Resistance of the Circuit Protective Conductor |
| Rn | Neutral Conductor Resistance | Vital for PSCC calculation |
| r1, rn, r2 | Ring Final Continuity | End-to-end resistances for ring circuit verification |
| IR | Insulation Resistance | Measured in MΩ at 500 V DC (usually) — min 1.0 MΩ |
| PSCC | Prospective Short Circuit Current | Max current between live conductors (L–N) |
| PEFC | Prospective Earth Fault Current | Max current between a live conductor and earth |
| PFC / Ipf | Prospective Fault Current | Highest of PSCC or PEFC — recorded on certificates |
| MFT | Multi-Function Tester | Primary instrument for the test sequence |
Protective Devices
| Abbreviation | Full Term | Note |
|---|---|---|
| MCB | Miniature Circuit Breaker | BS EN 60898 — Types B, C, D |
| MCCB | Moulded Case Circuit Breaker | Industrial, up to 2500 A, adjustable trip |
| RCD | Residual Current Device | Earth leakage / shock protection (30 mA typical) |
| RCCB | Residual Current Circuit Breaker | Leakage-only — must pair with an MCB |
| RCBO | Residual Current Breaker with Overload | MCB + RCD in one device |
| AFDD | Arc Fault Detection Device | 18th Edition — prevents fires from series/parallel arcs |
| SPD | Surge Protection Device | Limits transient overvoltages (lightning/switching) |
| ADS | Automatic Disconnection of Supply | Primary UK shock protection method (Reg 411) |
| HRC / HBC | High Rupturing / Breaking Capacity Fuse | BS 88 — very high fault current interruption |
| BS 1361 | Cartridge Fuse | Domestic supply heads, older consumer units |
| BS 3036 | Rewireable (Semi-enclosed) Fuse | Legacy — requires 0.725 derating (Ca × Cg × 0.725) |
Cable Types & Conductors
| Abbreviation | Full Term | Note |
|---|---|---|
| PVC | Polyvinyl Chloride | Standard thermoplastic — max 70 °C continuous |
| XLPE | Cross-Linked Polyethylene | Thermoset — max 90 °C, higher current for same CSA |
| LSF | Low Smoke and Fume | Reduced smoke vs standard PVC — public buildings |
| LSOH / LSZH | Low Smoke Zero Halogen | No corrosive acid gases when burning |
| SWA | Steel Wire Armoured | Mechanically protected, suitable for direct burial |
| MICC | Mineral Insulated Copper Clad | Inorganic — virtually indestructible by fire |
| FP200 | Fire Protected 200 | Silicone-insulated for life safety systems (fire alarms) |
| T&E | Twin and Earth (6242Y) | Standard domestic flat cable |
| CPC | Circuit Protective Conductor | The 'earth wire' within a circuit |
| CSA | Cross-Sectional Area | Conductor size in mm² |
Earthing Systems
| Abbreviation | Full Term | Note |
|---|---|---|
| TN-S | Terre-Neutral Separate | Separate earth via cable sheath — Ze ≈ 0.8 Ω |
| TN-C-S | Terre-Neutral Combined-Separate | PME supply — Ze ≈ 0.35 Ω |
| TT | Terre-Terre | Consumer's own earth electrode — requires RCD |
| IT | Isolated Terre | Specialist (medical IT systems) — source isolated from earth |
| PME | Protective Multiple Earthing | Most common TN-C-S in the UK |
| PEN | Protective Earth and Neutral | Single conductor carrying both functions (CNE) |
| CNE | Combined Neutral and Earth | Supply cable where N and E are one conductor |
Supply & Three-Phase
| Abbreviation | Full Term | Note |
|---|---|---|
| DNO | Distribution Network Operator | Manages local electricity grid (UKPN, WPD, etc.) |
| Cut-out | Service Head | Point of entry — contains DNO main fuse |
| Meter tails | Single-core cables | Connect cut-out → meter → consumer unit |
| L1, L2, L3 | Line Conductors (3-phase) | Brown, Black, Grey (harmonised colours) |
| N | Neutral | Blue conductor — return path to transformer |
| Vp | Phase Voltage | Line-to-Neutral — 230 V |
| VL | Line Voltage | Line-to-Line — 400 V |
Certificates & Building Regs
| Abbreviation | Full Term | Note |
|---|---|---|
| EIC | Electrical Installation Certificate | New installations, new circuits, CU changes |
| MEIWC | Minor Electrical Installation Works Certificate | Additions to existing circuits only |
| EICR | Electrical Installation Condition Report | Periodic inspection of existing systems |
| PIR | Periodic Inspection Report | Legacy term for EICR (pre-2011) |
| Part P | Building Regulations Part P | Electrical safety in dwellings — notifiable work |
| Part L | Building Regulations Part L | Conservation of fuel and power |
| C1 / C2 / C3 / FI | EICR Observation Codes | Danger / Pot. Dangerous / Improvement / Investigate |
Organisations & Standards
| Abbreviation | Full Term | Note |
|---|---|---|
| BS 7671 | Requirements for Electrical Installations | 18th Edition IET Wiring Regulations |
| IET | Institution of Engineering and Technology | Joint publishers of BS 7671 |
| BSI | British Standards Institution | National standards body |
| NICEIC | National Inspection Council for Electrical Installation Contracting | Competent person scheme |
| NAPIT | National Association of Professional Inspectors and Testers | Competent person scheme |
| ECA | Electrical Contractors' Association | Trade association |
| HSE | Health and Safety Executive | Enforces EAWR 1989 |
| EAWR | Electricity at Work Regulations 1989 | Statutory law — absolute duties on employers |
Fire Alarm Categories (BS 5839-1)
| Abbreviation | Full Term | Note |
|---|---|---|
| M | Manual System | MCPs only — no automatic detection |
| L1 | Maximum Life Protection | Detectors in all areas including voids |
| L2 | Life — Escape + High Risk | Escape routes plus kitchens, plant rooms |
| L3 | Life — Escape + Rooms Opening Onto | Escape routes and adjoining rooms |
| L4 | Life — Escape Routes Only | Corridors, stairways, lobbies |
| L5 | Life — Bespoke | Designed for a specific fire risk assessment |
| P1 | Property — Full Building | Detection throughout to minimise fire damage |
| P2 | Property — High Risk Areas | Detection in defined high-risk zones |
Emergency Lighting (BS 5266)
| Abbreviation | Full Term | Note |
|---|---|---|
| Maintained | Maintained Luminaire | Always on — theatres, cinemas |
| Non-maintained | Non-maintained Luminaire | On only when mains fails |
| Self-contained | Self-contained Unit | Each fitting has own internal battery |
| Central battery | Central Battery System | All fittings powered from one battery bank |
| BS 5266 | Emergency Lighting Standard | Covers design, installation, maintenance |
Installation Reference Methods
| Abbreviation | Full Term | Note |
|---|---|---|
| A | Enclosed in insulated wall | Worst case — conduit in thermally insulated wall |
| B | Enclosed in conduit/trunking on wall | Conduit or trunking surface-mounted |
| C | Clipped direct | Most common — cable clipped to wall/ceiling |
| D | Direct buried | In the ground or underground duct |
| E / F | Cable tray / ladder | Free air — best cooling |
| 100 / 101 | Flat T&E in insulated ceiling | 101 = >100 mm insulation contact |
| 102 / 103 | Cable in insulated stud wall | Common in timber-frame buildings |
Historical Terminology Changes
| Abbreviation | Full Term | Note |
|---|---|---|
| EEBADS → ADS | Automatic Disconnection of Supply | Simplified in 17th Edition |
| ELCB → RCD | Residual Current Device | Voltage-operated → current-operated |
| Phase → Line | Line conductor | 17th Edition — European harmonisation |
| PIR → EICR | Condition Report | 2011 — clarifies it is a report, not certificate |
| Red/Black → Brown/Blue | Harmonised colours | 2004/2006 transition |
Trade Slang vs Technical Terms
| Slang | Formal Term | Meaning |
|---|---|---|
| First fix | Roughing-in | Back boxes and cables before plastering |
| Second fix | Finishing | Sockets, switches, CU after plaster |
| Chasing | Raggles (Scotland) | Cutting wall slots for cables/conduit |
| Spur | Branch connection | Additional outlet from ring or radial |
| Capping | Protection strip | Metal/plastic over cables before plaster |
| Board / fusebox | Consumer unit | Main distribution panel in a dwelling |
Key Points
- - "Phase" was replaced by "Line" in the 17th Edition — both are still used on site
- - The fundamental inequality: Ib ≤ In ≤ Iz (design current ≤ device rating ≤ cable capacity)
- - ELCB (voltage-operated) is obsolete — always use RCD (current-operated)
- - FELV circuits are tested at 500 V DC (not 250 V) — they lack full separation from LV supply
- - BS 7671 is non-statutory but treated by HSE as the benchmark for compliance with EAWR 1989