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Home / Technical Articles / Assemblies of switchgear and control panels

Where are these assemblies used?

Switchgear and control panels are found in power generating stations, transformer stations, distribution substations, commercial and institutional buildings, industrial plants and factories, refineries, paper mills, metal smelters and any other place where electric energy is utilized or electric power is distributed to any number of zones.c

Assemblies of switchgear and control panels
Assemblies of switchgear and control panels (on photo SKEMA LV Switchgears)

There are a few common types of assemblies that cover almost any application. A broad classification according to the location of the switchgear assemblies is whether the gear is installed indoor or outdoor.

A further classification for the indoor gear is standard ventilated indoor, indoor with drip hood, indoor for location in sprinklers area, indoor in hazardous location, arc­proof (type a, b or c) and indoor in corrosive environment. Outdoor switchgear can also be further classified as whether it has an isle or not (walk ­in vs. non­walk ­in types) with or without a working area.

Another method of classifying the switchgear is whether it is a bottom or top entry , the power and control cables are entering from the bottom or the top of the gear.

Devices in Switchgear

The switchgear can contain as switching/interrupting device(s): a circuit breaker (c.b.), a switch/fuse combination, a contactor/fuse combination (for motor switching), for low v oltage (l.v.) assemblies: a switch or breaker in series with a contactor (for motor switching).

Certain configurations come only as non­draw ­out construction, others as draw­out. If special requirements for the gear are needed, the special property can be used as a criteria for defining the gear , for example, if dust tight enclosure is required due to the presence of dust (fine or course) in the atmosphere this gear is designated as dust tight.

For switchgear assemblies, as heat is generated from the high current flowing, a dust tight enclosure is almost impossible thus a dust proof one is used, instead. The major standards that govern the design, manufacture and testing of these assemblies are: CSA, ANSI, IEC, EEMAC, NEMA.

[pullquote_left]Switchgear assemblies and motor control centers (starters) line­ups can be classified according to their voltage classes. [/pullquote_left]The l.v. equipment is rated in the range of 120/208V single or three phase to 750V AC. The medium voltage ones are 2400/4160V to 44KV . The enclosures for all low voltage construction are metal enclosed. Some constructions include partitions and barriers to give a safer operation over and above the standard construction.

For medium voltage switchgear both construction types, metal clad and metal enclosed, are common. In this section the major components of the switchgear assemblies, motor starters and associated ancillaries will be given.

Major components

Low voltage switchgear assemblies

The main components are:

  • Molded case (MCB) or power (air magnetic) circuit breakers (draw­out or fixed) complete with or without integral overcurrent protection device (thermal­ magnetic,
  • Solid state or microprocessor based) with or without zone interlocking provision
  • Cradle (for drawout versions only)
  • Fixed potential and control power transformers
  • Current transformers
  • Interframe and back barriers
  • Main bus bars, run backs, bus risers and cable lugs (compression or mechanical)
  • Protective fuses for breaker control circuits, instrument compartments
  • Circuit breaker accessories, breaker lifting devices (integral with gear)
  • Fused or unfused interrupter switches
  • Protective and monitoring auxiliary relays
  • Metering devices (ammeters, voltmeters, watthourmeters, wattmeters and digital metering packages ­D.M.P.)
  • Control switches and indicating lights
Low voltage components
Low voltage components

Medium Voltage switchgear

The main components are:

  • Draw­out circuit breakers (oil, air, SF6, vacuum)
  • Switching device (load break or disconnect) with or w/o fuses (power current limiting or power expulsion type) with or w/o blown fuse indicator/actuator
  • Instrument transformers
  • Capacitor tripping device
  • Relays
  • Meters & instruments
  • Main bus
  • Control & indicating devices, jumpers, cable lugs, cable supports and potheads
  • Barriers and shutters
  • Instrument compartments
  • Test switches and breaker accessories
Medium voltage switchgear components
Medium voltage switchgear components

Low voltage motor control centers

For LV motor control centers the components are:

  • Combination motor starters
  • Instrument transformers
  • Motor protection devices
  • Main bus, cable entry compartments, vertical bus, control cables
  • Push buttons, pilot lights
  • Breaker or switch handle
  • Mounting pans
  • Programmable logic controllers PLC (processor module, I/O, network interface and other associated modules)
Low voltage motor control center components
Low voltage motor control center components

Medium voltage starters

For MV starters the main components are:

  • Contactors (vacuum and air)
  • Fused control transformer
  • Overload  protection
  • Current transformers
  • Instrument compartments
  • Meters
  • Auxilliary relays
  • Timers
  • Control devices
  • Multifunction motor protection relays
  • Indicating lights
  • Power fuses
  • Surge arresters

Switchgear Cubicle Types

There are a few distinct types of switchgear cubicles and are listed hereafter:

  • Incoming (main) cubicles
  • Transformer feeders
  • Bus tie (sectionalization)
  • Generator exciter control
  • Generator neutral cubicles
  • Induction motor control cubicle
  • Synchronous motor switching board
  • Potential transformer cubicles (used in conjunction with isolated phase bus in generating stations).
Other components that could be seen attached or connected to switchgear line­ups either or not to form a unit substation are: power transformers, low voltage bus duct/medium voltage bus or cable duct runs.

If the transformers are close coupled and installed indoor , then dry type transformers are used. If they are located outdoor and connected to the switchgear by non­segregated bus duct or cable duct or by a throat (with o/d switchgear) than they are of the oil filled type.

Another type of transformers that can be found indoors is the cast resin coil type.

To be continued…

Resource: Unknown

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. retregrgrfgr
    Jul 17, 2018

    i need some of the data regard failure rates of circuit breakers and relays and fuses and all electrical power distribution components for calculating mtbf and reliability of components and total system… urgent and must and should reply sir….. either data available or not….

  2. Purus
    Oct 23, 2015

    Thanks for the article edward. I am just studying more about switchgears for a project and find this really helpful…!

  3. Kalyan Mannava
    Sep 15, 2015

    sir, I want to know what kind of software used to find out or analyze the thermal stresses / mechanical stresses and other effects when the current is flowing through Low / Medium / High Voltage Panels. I would like to know by using software while loads occurs due to current flowing into the Bus Bars and other items where is the possibility of heat producing etc.

  4. rajesh
    May 26, 2015

    i need some of the data regard failure rates of circuit breakers and relays and fuses and all electrical power distribution components for calculating mtbf and reliability of components and total system… urgent and must and should reply sir….. either data available or not….

  5. Danish
    Apr 16, 2014

    1) Whats the basic difference between switchgear and electric panel ?
    2) Whats the basic difference between switchgear and switchboard ?
    3) Whats the basic difference between switchboard and electric panel ?
    4) Whats the basic difference between metal clad switchgear and metal enclosed switchgear ?


  6. aseye
    Jul 08, 2013

    Thanks for this article. I have found it tremendously useful in understanding the various bus arrangements in our switch yards here.

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