Glossary — GorkyCAD Pro

A

Arc Suppression Coil (Petersen Coil): A reactor connected between transformer neutral and ground to compensate capacitive earth-fault current. Used in 6-35 kV MV networks to reduce fault current and enable arc self-extinguishing.
Auto-Recloser (Recloser): A relay protection function that automatically re-energizes an MV line after tripping. Most overhead line faults are self-clearing (up to 80%). Auto-reclose restores supply in 0.5-2 seconds. Single-shot, two-shot, or accelerated.
ATS (Automatic Transfer Switch): A device that automatically switches power to a backup source (generator, second feeder) when the main source fails. Ensures supply continuity for critical loads.

B

Busbar: A conductor for distributing electricity inside a panel. Made of copper or aluminum. A comb busbar is a type of busbar for connecting MCBs of the same phase.
Busbar (in MV Switchgear): MV busbars in switchgear (6-35 kV) to which panels are connected. Single, double, or sectionalized. Sectionalizing improves reliability — during a fault, only one section is disconnected.
BIM (Building Information Modeling): Building Information Modeling technology. Electrical is part of the BIM model along with architecture and structures. Exchange via the IFC format. Mandatory for government orders in Russia since 2022.
Battery: A rechargeable chemical current source. In building electrical — part of UPS and backup power systems. Lead-acid (AGM, GEL) and lithium-ion (LiFePO4). Capacity measured in Ah.

C

Circuit Breaker (MCB): An electrical device that automatically opens a circuit during overload or short circuit. The primary protective element of an electrical network.
Cable: One or more insulated conductors in a common sheath. For building wiring, cables like VVG, NYM, PVC are used. Selection depends on load and installation conditions.
Conductor: A material (usually copper or aluminum) that conducts electric current well. Copper conductors are used in building wiring — they are more reliable than aluminum.
Cross-Section (Conductor): Conductor cross-sectional area in mm². Determines the allowable current. Standard range (Cu): 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50 mm². Outlets — 2.5 mm², lighting — 1.5 mm².
Cable Route: An assembly of cable, joint and termination kits, and support structures. In a project, designated by type, cross-section, length and installation method.
Cable Thermal Withstand: The cable's ability to withstand heating by S/C current during the protection tripping time. Verified: S ≥ Isc × √t / k, where k is the insulation material coefficient (115 for Cu/PVC).
Contactor: An electromagnetic device for frequent switching of power circuits. Unlike an MCB, does not protect against overloads. Used in control circuits for lighting, motors, heaters.
Current Transformer (CT): A transformer converting a large primary current (hundreds-thousands of A) into a small secondary current (1A or 5A) for measuring instruments and relay protection. Ratio: 100/5, 600/5, etc.
Cable Tray: A metal structure for exposed cable routing. Used in industrial and commercial buildings. Convenient for maintenance and adding new cables.
Cable Gland: A device for sealed cable entry into a panel or equipment enclosure. Ensures IP protection and mechanical cable fixation. Required to maintain the panel's protection rating.
Cable Joint / Cable Termination: A device for joining (joint) or terminating a cable. Ensures electrical insulation and mechanical sealing. Heat-shrink, cold-shrink, epoxy types.
Corrugated Conduit: Flexible plastic (PVC) or metal tube for cable routing. Protects from mechanical damage. PVC conduit — for concealed wiring, metal conduit — for exposed and hazardous areas.
Cable Clamp / P-Clip: A fixing product for securing a cable or corrugated conduit to a wall/ceiling. Consists of a dowel (plastic, inserted into a hole) and a clamp loop around the cable.
Cable Trunking / Raceway: A plastic or metal rectangular enclosure for exposed cable routing. Consists of a base and removable cover. Convenient for offices — allows adding cables without chasing walls.
Climate Rating (UHL, T, U): Placement category and climate rating per GOST 15150. U — moderate climate, UHL — moderate-cold, T — tropical. Affects equipment selection for boiler rooms, outdoor, basements.

D

Demand Factor (Kd): Ratio of design load to installed capacity. Accounts for the fact that not all loads run simultaneously. Kd = 0.3-0.8 for residential buildings (the more apartments, the lower the Kd).
Design Current (Icalc): Current calculated for selecting cable cross-section and MCB rating. Icalc = Pcalc / (√3 × U × cos φ) for three-phase or Icalc = Pcalc / (U × cos φ) for single-phase.
Distribution Board (DB): A metal or plastic enclosure with DIN rails housing MCBs, RCDs and other devices. Distributes electricity across consumer groups.
Distribution Network: Part of the electrical network from the main panel to end consumers. Includes cable lines, distribution boards, group circuits. Can be radial, trunk, or mixed topology.
Differential Protection: Protection comparing currents at the input and output of a protected element (transformer, line, busbar). When a current difference (leakage) occurs — instantaneous trip. The basis of relay protection.
Disconnector / Isolator: A medium-voltage device for creating a visible circuit break (off-load disconnection). Has no arc-quenching chambers. Used for safe maintenance and repair of equipment.
DIN Rail: Standard mounting rail 35 mm wide for installing modular equipment in panels (MCBs, RCDs, relays). International standard IEC 60715. Material: galvanised steel.
Derating Factor: A coefficient reducing cable ampacity depending on: number of cables in a bundle, ambient temperature, installation method. Per IEC 60364 / IS 732 derating tables.

E

Electrical Wiring: The totality of wires and cables with fixings and protective structures. Can be concealed (chased in plaster) or exposed (in trunking, on trays).
Earthing / Grounding: Intentional electrical connection to earth to protect people from electric shock. Can be functional (TN-S, TN-C-S) and protective (PE conductor).
Earthing Switch: A disconnector that connects a de-energized circuit section to ground for safe working. First the main disconnector is opened, then the earthing switch is closed. Has mechanical interlocking.
Earth Fault (in MV): Insulation failure between a phase and ground. In 6-35 kV networks — the most common fault type (70-90%). Current depends on neutral earthing: isolated — small, compensated — residual, resistive — active.
Energy Meter / Electricity Meter: A device for measuring consumed electricity (kWh). Direct connection — up to 100 A. With current transformers — for larger currents. Modern meters have digital interfaces and remote reading.
ELCB (Earth Leakage Circuit Breaker): An earth leakage protection device. In modern installations, replaced by RCDs. Distinguish between voltage-operated ELCB (obsolete) and current-operated (RCD/RCCB).
Electrical Schematic / Circuit Diagram: A graphical representation of electrical connections between components. Schematic (shows all elements and connections), single-line (simplified), wiring (shows actual layout).
Enclosure Protection Degree: Classification by IP Code (IEC 60529). Applied to panels, outlets, lights. Determines suitability for installation in dry/damp/dusty rooms and outdoors.

F

Final Circuit / Group Circuit: The line from the panel to end consumers (outlets, lights). Each group circuit is protected by a separate MCB. No more than 20 points per outlet group is recommended.
Fuse: A protective device that opens a circuit at a current above the rated value by melting a calibrated element. Unlike MCBs — single-use. Used in power circuits (NH, blade fuses) and electronics.

G

Grounding Electrode / Earth Loop: A system of metal electrodes buried in the ground to create reliable earthing. Loop resistance — no more than 4 Ohm for 380/220 V per PUE/IEC.
Grounding Electrode: A metal rod, angle, strip or pipe buried in the ground to create electrical contact with the soil. Vertical (rods 2-3 m) and horizontal (strips). Material: galvanised steel, copper.
Gas-Insulated Switchgear (GIS): Compact MV switchgear with SF₆ insulation. 5-10 times smaller than air-insulated switchgear. Used in confined spaces (urban substations, underground, offshore platforms).

H

Harmonic Distortion (THD): Distortion of the sinusoidal voltage/current waveform due to non-linear loads (LEDs, VFDs, computers). Measured in % THD. Per IEEE 519 — typically max 5-8% for low voltage.
Harmonic Filter: A device for suppressing harmonic distortion in the electrical network. Passive (LC filters) and active (APF — Active Power Filter). Used in networks with many non-linear loads.

I

Installed Capacity (Pinst): The sum of rated powers of all electrical loads at a facility. Differs from design load by the demand factor (Kd < 1), as all equipment rarely runs simultaneously.
Inrush Current: A brief (fraction of a second) current spike when starting an electric motor, transformer, or large lighting load. Can exceed rated current by 5-10 times. Considered when selecting MCBs and cable size.
IEC (International Electrotechnical Commission): International Electrotechnical Commission. Develops standards (IEC 60364 — low-voltage installations, IEC 60909 — short-circuit currents). National codes like PUE are based on them.
IP Rating (Ingress Protection): International classification of enclosure protection against dust and moisture per IEC 60529. First digit (0-6) — dust protection, second (0-9) — water. IP44 — splash protection, IP65 — full dust and water protection.
Inverter: A device that converts DC to AC. Used in solar power plants, UPS, VFDs. Parameters: power (kVA/kW), output waveform (pure/modified sine wave).

J

Junction Box: A box for joining, branching and splicing cables. Provides access to connections for maintenance. IP rating selected per location (IP20 — dry, IP44 — damp, IP65 — outdoor).

L

LED Lighting: Lighting based on light-emitting diodes. Consumes 5-10 times less electricity than incandescent lamps. Service life — 30,000-50,000 hours. Standard for modern projects.
Lightning Rod / Air Terminal: The upper part of lightning protection that intercepts a direct lightning strike. Rod, catenary wire, and mesh types. Protection zone calculated per IEC 62305 / IS 2309.
Lightning Protection System (LPS): A set of devices to protect a building from direct lightning strikes: air terminal, down conductors, earthing system. Four protection levels (I-IV) per IEC 62305.

M

Main Switchboard (MSB): The panel at the building power supply entry point. Receives electricity from the external grid and distributes it to consumers. Contains main breaker, metering devices, RCDs.
MDB (Main Distribution Board): The central panel of a building, receiving power from the transformer substation. Distributes electricity to floor and sectional panels. The highest-power panel in the hierarchy.
Motor Starter / Magnetic Starter: A contactor with thermal overload relay for motor control and protection. Protects against overload (thermal relay) and phase loss. Used in pumps, fans, compressors.
Medium Voltage (MV): Voltage class from 1 kV to 35 kV (per IEC 60038). Used for power distribution from substations to transformer points. Main levels: 3.3 kV, 6.6 kV, 11 kV, 22 kV, 33 kV.
MV Switchgear (Switchgear Panel): A medium-voltage cabinet (6-35 kV) containing a circuit breaker, disconnector, CT/VT. Used at substations and distribution points for power reception and distribution.
MV Cable: A power cable for 6-35 kV. Has reinforced insulation (XLPE/cross-linked polyethylene, paper-oil). Laid from MV switchgear to substations or between substations.
MV Cable Joint / MV Termination: A joint or termination for 6-35 kV cable. Heat-shrink or cold-shrink types. Requires highly qualified installers — mistakes lead to insulation breakdown.
MV Fuse: A fuse for protecting transformers and substations from S/C currents. Types: quartz-filled, transformer-rated. Breaking capacity — up to 40 kA. Installed in MV switchgear.
MCB (Miniature Circuit Breaker): Miniature circuit breaker. Standard protection for group circuits in panels. Characteristics: B (household), C (commercial/industrial), D (motors with high inrush current).
MCCB (Molded Case Circuit Breaker): Molded case circuit breaker. Used on main incomers and for high-power consumers (currents from 100 to 2500 A). Has adjustable trip settings.

N

Neutral Earthing Mode: The method of earthing the transformer neutral: solidly earthed (TN), isolated (IT), through impedance. For residential buildings — solidly earthed neutral (TN-C-S).

O

Overhead Line (OHL): An outdoor power transmission line with conductors supported on poles via insulators. 6-35 kV OHL — distribution lines. Above 35 kV — transmission lines. Subject to ice, wind, lightning.

P

Power Factor (cos φ): Ratio of active power to apparent power. Shows how efficiently electricity is used. For household loads cos φ ≈ 0.9-1.0, for motors — 0.7-0.85.
Power Calculation / Load Calculation: Determination of design load (Pcalc) for selecting cable cross-section and transformer. Considers installed capacity and demand/simultaneity factors per SP 256 / IEC.
Protective Earth Conductor (PE): A conductor connecting equipment enclosures to earth. Ensures safety: during insulation failure, current goes to earth rather than through a person. Yellow-green insulation.
PEN Conductor: Combined protective earth and neutral conductor in the TN-C-S system from substation to main switchboard. Separated into PE and N at the entry. Minimum cross-section — 10 mm² (Cu) or 16 mm² (Al).
Potential Equalisation / Bonding: Electrical connection of all exposed conductive parts (pipes, enclosures, baths) with the earthing system to eliminate potential differences. Main (MEB) and supplementary (SEB) bonding.
Power Transformer: A high-power transformer (from 25 kVA to hundreds of MVA) for power transmission and distribution. Oil-immersed (with tank) and dry-type (cast resin).
Package Substation / KTP: A factory-built transformer substation. Receives 6-35 kV, steps down to 0.4 kV. Consists of MV section, transformer, and LV panel. Capacity: 25-2500 kVA.
Protection Relay / P&A (Protection & Automation): A set of devices for protecting MV lines, transformers, and busbars from S/C and abnormal modes. Functions: overcurrent (OC), short-circuit (SC), differential busbar protection, auto-reclose.
PLC (Programmable Logic Controller): An industrial computer for process automation. Receives sensor signals, processes per program, controls actuators. In electrical — lighting, ventilation, panel control.
PUE (Electrical Installation Code): The main regulatory document of Russia for design and installation of electrical installations up to 500 kV. Contains requirements for wiring, earthing, protection, lighting. 7th edition is current.
Phase (L1/L2/L3): A conductor with voltage relative to earth and neutral. In a three-phase network — three phases (L1, L2, L3) shifted 120°. Household outlets — 220 V (phase-neutral), industrial — 380 V (phase-phase).

R

Rated Current (In): The current at which electrical equipment can operate indefinitely without overheating. For MCBs, standard ratings: 6, 10, 16, 20, 25, 32, 40, 50, 63 A.
RCBO (Residual Current Circuit Breaker with Overcurrent): A device combining MCB (overload and short-circuit protection) and RCD (leakage current protection) functions. Saves space in the panel.
RCD (Residual Current Device): A protective device that disconnects the circuit when current leaks to earth (e.g., through a person). Does not protect against overload or S/C — an MCB is needed for that.
RCD / GFCI (Ground Fault Circuit Interrupter): Residual current protective device. In US terminology — GFCI. Disconnects when differential current (leakage) exceeds the setting: 10 mA (wet rooms), 30 mA (household), 100-300 mA (fire protection).
Reactive Power Compensation: Installation of capacitor banks to improve cos φ. Reduces line losses and transformer load. Relevant for workshops with motors — raises cos φ from 0.7 to 0.95.
Renewable Energy (RES): Energy from renewable sources: sun, wind, water, biomass. In building electrical — rooftop solar panels with inverter. Requires grid operator approval (interconnection agreement).

S

Single-Line Diagram (SLD): A simplified power supply diagram where all phases are shown as one line. Contains load data, breakers, cables, S/C currents. The main project document.
Short Circuit (S/C): An unintended connection between phase and neutral/earth conductors with very low resistance. Causes a sharp current spike, heating and fire risk. Protection — circuit breakers and fuses.
Short-Circuit Current (Isc): Current flowing during a short circuit. Can reach tens of kA. Determines required MCB breaking capacity (6 kA, 10 kA, 15 kA) and equipment thermal withstand.
Selectivity / Discrimination: A protection property where only the breaker closest to the fault trips during a short circuit, while the rest remain on. Ensures continuity for other consumers.
SPD (Surge Protective Device): Surge protective device. Protects equipment from lightning strikes and switching surges. Classes: Type I (lightning), Type II (switching), Type III (fine protection).
SF₆ Circuit Breaker: A medium/high-voltage circuit breaker using SF₆ gas as the arc-quenching medium. Excellent arc-extinguishing capability. Used at 35 kV and above.
Surge Arrester (MOA): A device protecting MV equipment from lightning and switching overvoltages. Based on metal-oxide varistors (ZnO). Unlike spark-gap arresters — no gap, more reliable.
Solar Panel (PV Module): A device for converting solar energy into DC electricity. Consists of photovoltaic cells (usually silicon). Residential panel power — 300-600 W. Requires an inverter for grid connection (220/380 V).
Short-Circuit Calculation: Determination of short-circuit current to verify MCB breaking capacity and cable thermal withstand. Per GOST 28249 (Russia) or IEC 60909 (international).
Single-Phase Network: A power supply system with one phase (220/230 V). Standard for apartments and small houses. Maximum allocated power — typically up to 15 kW.

T

TN-C-S System: An earthing system where neutral (N) and protective earth (PE) conductors are combined at the entry (PEN) and separated in the main switchboard. The most common system in Russia.
Two-Way Switch / Intermediate Switch: A switch that allows controlling lighting from two (two-way) or three+ (intermediate) locations. Used in corridors, staircases, bedrooms.
Transformer: A device for converting AC voltage. Steps down high voltage (6-10 kV) to household level (220/380 V). The basis of substations.
Three-Phase Network: A power supply system with three phases (380/400 V line, 220/230 V phase). Provides higher power than single-phase. Standard for apartment buildings and industry.

U

UPS (Uninterruptible Power Supply): A battery-backed device that maintains power to the load during a mains outage. Offline (standby) — cheap but with delay. Online (double conversion) — instant, for servers and medical equipment.

V

Voltage Relay / Undervoltage-Overvoltage Relay: A device that disconnects power when voltage goes beyond acceptable limits (e.g., <170 V or >270 V). Protects home appliances from voltage surges and neutral failure.
VFD (Variable Frequency Drive): A device for smooth speed control of an induction motor by varying the supply voltage frequency. Saves 30-50% energy in pumps and fans.
Vacuum Circuit Breaker (VCB): A medium-voltage circuit breaker where arc extinction occurs in a vacuum chamber. Advantages: high reliability, minimal maintenance, no oil. Standard for MV switchgear 6-35 kV.
Voltage Transformer (VT / PT): A transformer converting high voltage (6-35 kV) to low voltage (100 V) for measuring instruments and relay protection. Accuracy class: 0.2, 0.5, 1.0, 3.0.
Voltage Drop: Voltage difference between the beginning and end of a line due to conductor resistance. Per PUE/IEC — max 5% from main panel to end consumer. The main criterion for cable cross-section selection.
VDE (Association for Electrical, Electronic & Information Technologies): German association for electrical engineering. VDE standards are among the strictest in the world. Cables with VDE marking guarantee top insulation quality.

Z

Zero-Sequence CT / CBCT: A current transformer for earth-fault detection in MV networks. Surrounds all three phases simultaneously. Upon earth leakage — sends a signal to relay protection.

Glossary of Electrical Terms

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