Electrical & Switchgear Glossary
Clear, factual definitions of the low-voltage switchgear, protection and Multispan control terms used across our products and guides — for engineers, panel builders and buyers in the UAE.
Switchgear & panels
MDB (Main Distribution Board)
An MDB (Main Distribution Board) is the primary low-voltage panel that receives incoming power from the DEWA transformer or supply and distributes it to sub-boards and major loads. It houses the main incomer breaker, busbars, and outgoing feeders, forming the central hub of a building's LV electrical distribution.
SMDB (Sub-Main Distribution Board)
An SMDB (Sub-Main Distribution Board) is a secondary LV panel fed from the MDB that distributes power to a specific zone, floor, or group of final distribution boards. It reduces cable runs and localizes protection, sitting between the main board and end-load DBs in the distribution hierarchy.
FDB (Final Distribution Board)
An FDB (Final Distribution Board) is the last panel in the distribution chain, feeding individual circuits such as lighting, sockets, and small equipment. Typically fitted with MCBs or RCBOs, it is the point where power is divided into the final branch circuits serving end users directly.
MCC (Motor Control Centre)
An MCC (Motor Control Centre) is a switchgear assembly grouping multiple motor starters, contactors, overload relays, and protective devices in a single enclosure. It controls and protects electric motors for pumps, HVAC, and industrial drives, often with drawer or fixed modules for centralized motor management and monitoring.
ATS (Automatic Transfer Switch)
An ATS (Automatic Transfer Switch) automatically switches an electrical load between two power sources, typically the DEWA mains and a standby generator, on detecting supply failure. It ensures continuous power to critical loads, transferring within seconds and returning to mains once normal supply is restored.
Busbar
A busbar is a rigid metallic conductor, usually copper or aluminium, that carries and distributes high current within a switchboard. It connects incoming supply to multiple outgoing circuits, providing a low-impedance common connection point. Busbar ratings and short-circuit withstand are central to panel design under IEC 61439.
Single-Line Diagram (SLD)
A Single-Line Diagram (SLD) is a simplified schematic representing a power system using single lines and standard symbols for breakers, transformers, busbars, and feeders. It shows ratings, protection, and connectivity at a glance and is a mandatory document for DEWA approval and switchgear manufacturing.
Form of Separation
Form of Separation defines how a switchboard's internal compartments are segregated by barriers into Forms 1 to 4, isolating busbars, functional units, and terminals. Higher forms (e.g. Form 3b, Form 4b) improve operator safety and allow maintenance on one circuit while others remain live, per IEC 61439.
IP Rating (Ingress Protection)
An IP Rating (Ingress Protection), defined by IEC 60529, is a two-digit code stating an enclosure's protection against solids and liquids. The first digit covers dust and objects, the second water. For example, IP54 panels resist dust and splashing water, common for indoor UAE switchgear installations.
Enclosure
An enclosure is the metal or non-metallic housing that contains switchgear components, protecting them from dust, moisture, and contact while safeguarding personnel from live parts. Its IP rating, sheet-steel gauge, powder coating, and ventilation are selected to suit the installation environment, whether indoor, outdoor, or harsh UAE conditions.
Incomer
An incomer is the main incoming circuit breaker or switch through which supply enters a distribution board or switchgear panel. Usually an ACB or MCCB, it provides overall isolation, protection, and control for everything downstream, and is rated to match the transformer or upstream source capacity.
Distribution Board (DB)
A Distribution Board (DB) is an enclosure that divides an incoming electrical supply into multiple outgoing circuits, each protected by its own breaker or fuse. It provides isolation, protection, and control at a given point in the system and forms the building block of LV power distribution.
Panel Building
Panel building is the fabrication and assembly of electrical switchgear, involving enclosure manufacture, busbar systems, wiring, mounting of breakers and components, testing, and labelling to design and standards. Al Misbah Al Sehri manufactures LV panels in Dubai using genuine multi-brand components and compliance with IEC 61439.
Cable Gland
A cable gland is a mechanical fitting that secures a cable where it enters an enclosure or panel, providing strain relief, sealing against dust and moisture, and, for armoured cables, earth continuity. Rated by IP ingress protection and cable type, glands maintain enclosure integrity in UAE switchgear and industrial installations.
Protection, breakers & relays
Discrimination / Selectivity
Discrimination, or selectivity, is the coordination of protective devices so that only the breaker nearest a fault trips, leaving upstream devices closed. This isolates the faulty circuit while keeping the rest of the installation energized, minimizing downtime and improving reliability, a key requirement in critical LV distribution design.
Prospective Short-Circuit Current & Icw
Prospective short-circuit current is the maximum fault current a system can deliver at a point, determining device breaking capacity. Icw (rated short-time withstand current) is the RMS current a busbar or assembly can carry for a specified time (e.g. 1 second) without damage, verifying switchgear robustness under IEC 61439.
MCB (Miniature Circuit Breaker)
An MCB (Miniature Circuit Breaker) is an automatic electromechanical switch that protects low-voltage circuits from overload and short-circuit currents by tripping instantly. Rated typically up to 125A, it is resettable (unlike a fuse) and common in UAE final distribution boards under IEC 60898, with B, C, and D tripping curves.
MCCB (Moulded Case Circuit Breaker)
An MCCB (Moulded Case Circuit Breaker) is a protective device housed in an insulated moulded case, rated from roughly 16A up to 1600A, protecting circuits against overload and short circuit. It offers adjustable thermal-magnetic or electronic trip settings and higher breaking capacity than an MCB, governed by IEC 60947-2 in UAE switchgear panels.
ACB (Air Circuit Breaker)
An ACB (Air Circuit Breaker) is a low-voltage breaker using air at atmospheric pressure to extinguish the arc, rated from about 630A to 6300A. Used as main incomers in main distribution boards, it features electronic trip units, adjustable protection, and drawout construction, complying with IEC 60947-2 in UAE panels.
RCCB / ELCB (Residual Current / Earth Leakage Circuit Breaker)
An RCCB (Residual Current Circuit Breaker), historically called an ELCB (Earth Leakage Circuit Breaker), detects imbalance between line and neutral currents caused by earth leakage and disconnects to prevent electric shock. Common sensitivities are 30mA (personal protection) and 100/300mA (fire protection), per IEC 61008, standard in UAE and DEWA installations.
RCBO (Residual Current Breaker with Overcurrent protection)
An RCBO (Residual Current Breaker with Overcurrent protection) combines the functions of an RCCB and an MCB in one device, providing earth-leakage, overload, and short-circuit protection together. It protects a single circuit so a fault trips only that circuit, improving discrimination. Governed by IEC 61009 and widely used in UAE distribution boards.
Contactor
A contactor is an electrically controlled switch used to make and break power circuits under load, typically for motors, lighting, and heating. Energizing its coil closes the main contacts; de-energizing opens them. Rated by AC utilization category (AC-3 for motors) under IEC 60947-4-1, it is a core control component in UAE switchgear.
Overload Relay (Thermal Overload Relay)
An overload relay is a protective device that guards motors against sustained overcurrent (overload) by tripping when current exceeds a set threshold for a set time. Thermal types use bimetallic strips; electronic types sense current directly. Paired with a contactor to form a starter, it complies with IEC 60947-4-1 in UAE motor control.
Isolator (Disconnector)
An isolator, or disconnector, is a switch that provides a visible, guaranteed open break to isolate a circuit or equipment for safe maintenance. It is operated off-load (no current flowing) unless rated as a switch-disconnector. Under IEC 60947-3, it ensures electrical isolation and is mandatory for safe servicing in UAE installations.
Fuse
A fuse is a simple protective device containing a metal element that melts and breaks the circuit when current exceeds a safe value, guarding against overload and short circuit. Unlike breakers, it must be replaced after operating. Types include HRC (High Rupturing Capacity) fuses used in UAE distribution, rated per IEC 60269.
DOL Starter (Direct-On-Line Starter)
A DOL (Direct-On-Line) starter connects a motor directly to full supply voltage, using a contactor and overload relay to start and protect it. Simple and low-cost, it delivers high starting current (6–8 times rated) and torque, suited to small motors typically up to about 7.5kW in UAE industrial applications.
Star-Delta Starter
A star-delta starter reduces motor starting current by initially connecting windings in star configuration, then switching to delta for full running. This lowers inrush current to roughly one-third of DOL, easing supply stress on larger motors (typically above 7.5kW). It uses three contactors and a timer, common in UAE industrial motor control.
Protection Relay (VPR / SVR / SPP - Voltage/Phase Protection Relay)
A protection relay monitors electrical parameters and disconnects or signals a fault when limits are exceeded. VPR (voltage protection relay), SVR (single-phase voltage relay), and SPP (single-phasing preventer) guard motors and equipment against over/under-voltage, phase failure, and unbalance. Multispan protection relays, distributed by Al Misbah Al Sehri, safeguard pumps, compressors, and industrial machinery.
Single-Phasing Preventer (SPP)
A single-phasing preventer detects loss of one phase in a three-phase supply and trips the motor before damage occurs. Running a three-phase motor on two phases causes severe overheating and winding burnout. Multispan single-phasing preventers, supplied by Al Misbah Al Sehri in the UAE, protect motors, pumps, and compressors from costly phase-failure faults.
Control instruments
PID Control (Proportional-Integral-Derivative Control)
PID control is a feedback algorithm that continuously calculates error between a setpoint and measured value, then applies proportional, integral, and derivative corrections to drive output smoothly to target. Widely used in Multispan temperature and process controllers, it delivers precise, stable regulation with minimal overshoot for ovens, furnaces, and industrial heating.
On/Off Control (Two-Position Control)
On/off control is the simplest control mode, switching the output fully on or off when the measured value crosses the setpoint, usually with a hysteresis band to prevent rapid chattering. Common in Multispan thermostats and basic temperature controllers, it suits applications tolerating small cycling swings, such as refrigeration, water heaters, and simple ovens.
Thermocouple (Type J / Type K)
A thermocouple is a temperature sensor made of two dissimilar metal wires joined at a junction, producing a small voltage proportional to temperature. Type J (iron-constantan) suits up to about 750 degC; Type K (chromel-alumel) reaches roughly 1260 degC. Multispan controllers accept J and K inputs for furnaces, ovens, and industrial heating.
PT-100 RTD (Platinum Resistance Temperature Detector)
A PT-100 is an RTD temperature sensor whose platinum element measures 100 ohms at 0 degC, with resistance rising predictably as temperature increases. It offers high accuracy and stability over roughly -200 to +600 degC, making it ideal for precision process control. Multispan controllers accept PT-100 inputs for laboratory, food, and industrial applications.
SSR (Solid State Relay)
An SSR is an electronic switching device that turns loads on and off using semiconductors instead of mechanical contacts, giving silent, fast, arc-free operation and long life. Frequently paired with Multispan PID controllers for precise heater cycling, SSRs handle millions of switching operations, ideal for temperature control where relays would wear out quickly.
Temperature Controller
A temperature controller is an instrument that reads a sensor (thermocouple or RTD), compares the reading to a setpoint, and switches heating or cooling outputs to maintain target temperature. Multispan, distributed by Al Misbah Al Sehri as authorized UAE/GCC distributor, offers on/off and PID temperature controllers for ovens, furnaces, refrigeration, and process industries.
Humidity Controller (RH - Relative Humidity)
A humidity controller measures relative humidity (RH), the percentage of moisture in air versus saturation, and switches humidifiers, dehumidifiers, or ventilation to maintain a target level. Multispan humidity controllers, available from Al Misbah Al Sehri in the UAE, serve incubators, cold storage, greenhouses, textile, and pharmaceutical environments requiring stable moisture control.
SMPS (Switched-Mode Power Supply)
An SMPS is a power supply that converts AC or DC to regulated DC using high-frequency switching, offering compact size, high efficiency, and wide input range compared to linear supplies. Multispan SMPS units, distributed by Al Misbah Al Sehri in the UAE/GCC, power control panels, PLCs, sensors, and instrumentation at 12V, 24V, and other DC rails.
Modbus RS-485
Modbus RS-485 is an industrial serial communication protocol running over two-wire RS-485 physical layer, allowing multiple devices to share data on a single bus over long distances with noise immunity. Multispan meters, controllers, and data loggers use Modbus RS-485 for SCADA and energy-monitoring integration, enabling centralized reading and control across panels and plants.
Data Logger
A data logger is an instrument that records measured values such as temperature, humidity, or electrical parameters over time to internal memory or a communication link, enabling trend analysis and compliance records. Multispan data loggers, supplied by Al Misbah Al Sehri in the UAE, serve cold-chain monitoring, energy audits, and process validation in pharma and food industries.
Hysteresis (Deadband)
Hysteresis, or deadband, is the deliberate gap between the switch-on and switch-off points of a controller, preventing rapid on/off cycling when the measured value hovers near the setpoint. For example, a heater set to 50 degC with 2 degC hysteresis switches off at 51 degC and back on at 49 degC, protecting relays and loads.
Power quality
Surge Protection Device (SPD)
An SPD (Surge Protection Device) diverts transient overvoltages, from lightning or switching surges, safely to earth, protecting equipment and wiring from voltage spikes. Classified Type 1, 2, or 3 by location and energy handling under IEC 61643, SPDs are increasingly specified in UAE panels to protect sensitive electronics and DEWA-connected systems.
Power Factor (PF)
Power factor is the ratio of real power (kW) doing useful work to apparent power (kVA) drawn from the supply, expressed between 0 and 1. A low power factor means wasted capacity and higher DEWA demand charges. Correcting it with capacitor banks toward unity improves efficiency and avoids utility penalties in UAE industrial installations.
APFC / Capacitor Bank (Automatic Power Factor Correction)
An APFC panel with a capacitor bank automatically switches capacitors in and out to maintain optimal power factor as load varies, supplying reactive power locally. This reduces DEWA penalties, frees transformer capacity, and improves voltage. Al Misbah Al Sehri manufactures LV APFC panels and capacitor banks for UAE industrial and commercial facilities.
kVAR (Kilovolt-Ampere Reactive)
kVAR is the unit of reactive power, the non-working power that magnetizes motors and transformers but performs no useful output. Capacitor banks are rated in kVAR to offset the inductive reactive demand of a load, raising power factor. Correct kVAR sizing in APFC panels minimizes losses and utility charges in UAE installations.
Standards & compliance
DEWA Approval
DEWA Approval is the certification required from Dubai Electricity and Water Authority before LV switchgear and distribution boards are connected to the Dubai grid. It verifies that panel design, ratings, components, and single-line diagrams meet DEWA regulations, ensuring safety and compliance for electrical installations across the emirate.
IEC 61439
IEC 61439 is the international standard for low-voltage switchgear and controlgear assemblies, replacing IEC 60439. It defines design verification, testing, temperature rise, short-circuit withstand, and construction requirements. Compliance demonstrates that a panel is a verified assembly, and it is the benchmark for switchgear manufactured for UAE projects.
Breaking Capacity (Icu / Ics, kA)
Breaking capacity is the maximum fault current, in kiloamperes (kA), a circuit breaker can safely interrupt without damage. Icu is the ultimate rating (breaker may be unusable after); Ics is the service rating for repeated operation. Selected to exceed the prospective short-circuit current, per IEC 60947-2, critical for UAE panel safety.
Earthing (Grounding)
Earthing is the deliberate connection of electrical equipment and exposed metalwork to the earth, providing a low-resistance path for fault current and stabilizing voltage. It ensures protective devices trip on faults and prevents dangerous touch voltages. UAE and DEWA regulations mandate proper earthing systems (TN-S, TT) per IEC 60364 for installation safety.
CE Marking (Conformite Europeenne)
CE marking is a manufacturer's declaration that a product meets applicable European Union health, safety, and environmental directives, allowing sale within the European Economic Area. For electrical control instruments it signals compliance with Low Voltage and EMC directives. Al Misbah Al Sehri supplies CE-marked components and Multispan instruments meeting international quality and safety standards.
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