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Open demo See pricingThis reference lists 150 abbreviations used in design, installation and estimating, grouped by area. It is not a code: where a standard defines a term, the standard wins, and usage varies between countries and offices.
How to read this table
- The same letters can mean two things. CT is a current transformer, and cable tray in some offices. Context decides.
- Capitals matter. mA is a milliamp; MA is a mega-amp. m² is an area and M² is a typo.
- A legend beats a guess. Every issued drawing should carry one, even when the terms look obvious to you.
Power, energy and supply
| Abbr. | Meaning |
|---|---|
| AC | Alternating current |
| DC | Direct current |
| V | Volt |
| A | Ampere |
| W | Watt |
| VA | Volt-ampere, apparent power |
| kVA | Kilovolt-ampere |
| kW | Kilowatt |
| kWh | Kilowatt-hour, energy |
| kVAR | Kilovolt-ampere reactive |
| PF | Power factor |
| Hz | Hertz, frequency |
| RMS | Root mean square |
| THD | Total harmonic distortion |
| UPS | Uninterruptible power supply |
| PV | Photovoltaic |
| VFD | Variable frequency drive |
| VSD | Variable speed drive |
| ATS | Automatic transfer switch |
| G | Generator |
Protection and switchgear
| Abbr. | Meaning |
|---|---|
| MCB | Miniature circuit breaker |
| MCCB | Moulded case circuit breaker |
| ACB | Air circuit breaker |
| CB | Circuit breaker |
| RCD | Residual current device |
| RCCB | Residual current circuit breaker |
| RCBO | Residual current breaker with overcurrent protection |
| GFCI | Ground fault circuit interrupter |
| AFCI | Arc fault circuit interrupter |
| ELCB | Earth leakage circuit breaker |
| OCPD | Overcurrent protective device |
| SPD | Surge protective device |
| CT | Current transformer |
| PT | Potential transformer |
| SC | Short circuit |
| Isc | Short-circuit current |
| Icu | Rated breaking capacity |
| Ics | Service breaking capacity |
| In | Nominal current |
| Ir | Long-time setting current |
| Im | Instantaneous setting current |
| IΔn | Residual operating current |
| IP | Ingress protection rating |
| IK | Impact protection rating |
| O/L | Overload |
Cables, wiring and containment
| Abbr. | Meaning |
|---|---|
| XLPE | Cross-linked polyethylene |
| PVC | Polyvinyl chloride |
| LSZH | Low smoke zero halogen |
| SWA | Steel wire armour |
| MICC | Mineral insulated copper clad |
| NM-B | Non-metallic sheathed cable, US |
| AWG | American wire gauge |
| CSA | Cross-sectional area |
| CCC | Current-carrying capacity |
| CPC | Circuit protective conductor |
| N | Neutral |
| L | Line conductor |
| L1 | Phase 1 |
| L2 | Phase 2 |
| L3 | Phase 3 |
| T&E | Twin and earth |
| Uo | Phase-to-earth voltage |
| U | Phase-to-phase voltage |
| EMT | Electrical metallic tubing |
| IMC | Intermediate metal conduit |
| RMC | Rigid metal conduit |
| FMC | Flexible metal conduit |
| LFMC | Liquidtight flexible metal conduit |
| CPR | Construction Products Regulation class |
| NYY | PVC-insulated power cable |
| NYM | PVC-insulated installation cable |
Earthing and bonding
| Abbr. | Meaning |
|---|---|
| PE | Protective earth |
| PEN | Combined protective earth and neutral |
| EGC | Equipment grounding conductor |
| GEC | Grounding electrode conductor |
| MEB | Main equipotential bonding |
| TT | Earthing system, electrodes only |
| TN-S | Earth and neutral separate throughout |
| TN-C | Earth and neutral combined throughout |
| TN-C-S | Combined, then separate |
| IT | Isolated earth system |
| Zs | Earth fault loop impedance |
| Ze | External loop impedance |
Standards and regulation
| Abbr. | Meaning |
|---|---|
| NEC | National Electrical Code, US |
| NFPA | National Fire Protection Association |
| IEC | International Electrotechnical Commission |
| IEEE | Institute of Electrical and Electronics Engineers |
| ANSI | American National Standards Institute |
| UL | Underwriters Laboratories |
| NEMA | National Electrical Manufacturers Association |
| BS | British Standard |
| BS 7671 | UK wiring regulations |
| EN | European norm |
| CE | Conformité Européenne marking |
| UKCA | UK conformity marking |
| ATEX | EU explosive atmospheres directives |
| OSHA | Occupational Safety and Health Administration |
| AHJ | Authority having jurisdiction |
| AS/NZS 3000 | Australian and New Zealand wiring rules |
| IEC 60364 | Low-voltage electrical installations |
| IEC 61439 | Low-voltage switchgear assemblies |
| IEC 60529 | Degrees of protection, IP code |
| IEC 62305 | Lightning protection |
| IEC 60079 | Explosive atmospheres |
Drawings, systems and project terms
| Abbr. | Meaning |
|---|---|
| SLD | Single-line diagram |
| BOM | Bill of materials |
| BOQ | Bill of quantities |
| GA | General arrangement drawing |
| I/O | Input and output list |
| PLC | Programmable logic controller |
| HMI | Human-machine interface |
| SCADA | Supervisory control and data acquisition |
| LV | Low voltage |
| MV | Medium voltage |
| HV | High voltage |
| ELV | Extra-low voltage |
| MDB | Main distribution board |
| DB | Distribution board |
| MCC | Motor control centre |
| MSB | Main switchboard |
| TPN | Triple pole and neutral |
| SPN | Single pole and neutral |
| SP | Single pole |
| DP | Double pole |
| TP | Triple pole |
| 4P | Four pole |
| MEP | Mechanical, electrical and plumbing |
| EPC | Engineering, procurement, construction |
| RFI | Request for information |
| T&M | Time and materials |
| Rev | Revision |
| NTS | Not to scale |
| FFL | Finished floor level |
| QTY | Quantity |
Loads, motors and lighting
| Abbr. | Meaning |
|---|---|
| FLA | Full load amps |
| FLC | Full load current |
| LRA | Locked rotor amps |
| MCA | Minimum circuit ampacity |
| MOP | Maximum overcurrent protection |
| LED | Light-emitting diode |
| CCT | Correlated colour temperature |
| CRI | Colour rendering index |
| lm | Lumen |
| lx | Lux |
| cd | Candela |
| K | Kelvin, colour temperature |
| LPD | Lighting power density |
| DALI | Digital addressable lighting interface |
| PIR | Passive infrared sensor |
| EM | Emergency lighting circuit |
Ten pairs that get confused
| Pair | The difference that matters |
|---|---|
| MCB / MCCB | Miniature device for final circuits versus moulded-case breaker with adjustable settings |
| RCD / RCBO | Residual current only versus residual plus overcurrent in one device |
| Icu / Ics | Rated breaking capacity versus the service value it can interrupt repeatedly |
| In / Ir | Device rating versus the setting you actually apply |
| PE / PEN | Protective earth versus a conductor carrying both earth and neutral |
| TN-S / TN-C-S | Earthing separated at the origin versus separated partway along |
| Uo / U | Phase-to-earth versus phase-to-phase. Mixing them changes every calculation |
| kVA / kW | Apparent power versus real power; 100 kVA is not 100 kW |
| RCCB / ELCB | Current-operated versus the older term that also covered voltage-operated devices |
| NTS / scale bar | Not to scale, never measure versus calibrated scale, measure after checking |
Using abbreviations in schedules and drawings
- Expand on first use. Write “residual current breaker with overcurrent protection (RCBO)” once, then abbreviate.
- Keep one legend per project. Multiple legends drift, and a drifted legend is worse than none.
- Match schedule to plan. If the plan says S12, the schedule says S12.
GorkyCAD Pro generates circuit and panel schedules from the drawing model, so labels stay consistent and the legend is part of the export. It runs in a browser, with no offline mode, and its 41 automated checks are design aids, not certification. See the electrical drawing checklist and house wiring plan software.
Put the legend to work. Open the 41-rule check on a demo project: the legend drives the panel schedule, so labels cannot drift between drawing and export. The 41-rule design check explains each rule.
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Open demo See pricingFrequently asked questions
Why do the same abbreviations mean different things in different countries?
National codes evolved separately. GFCI and ELCB describe similar protective ideas from different traditions, and IEC uses Uo/U where NEC texts say line-to-neutral and line-to-line. Read the legend of the drawing in front of you.
Is MCCB the same as MCC?
No. MCCB is a moulded case circuit breaker; MCC is a motor control centre, an assembly rather than a device. This pair causes real procurement errors.
Should I write mm² or mm2?
mm² is correct and unambiguous. mm2 is common in plain-text systems that cannot render superscripts. Pick one and use it everywhere.
What does IP44 mean?
The first digit is solids, the second is water: IP44 means protected against objects over 1 mm and against splashing water. Exact definitions live in IEC 60529.
Do I need to define abbreviations the client already knows?
Yes. The installer, the inspector and the next engineer read the same file, often years later.
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Sources
- IEC Electropedia — electrotechnical vocabulary: https://www.electropedia.org/
- IEC 60617 — graphical symbols for diagrams: https://std.iec.ch/iec60617
- IEEE 315 — graphical symbols for electrical diagrams: https://standards.ieee.org/ieee/315/2352/
- NFPA 70, National Electrical Code: https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70