Switchgear selection is a critical part of electrical system design because the switchgear must safely switch, protect, isolate, and distribute electrical power under both normal and abnormal operating conditions.

Choosing switchgear based only on system voltage or rated current is not sufficient. Engineers and procurement teams also need to evaluate short-circuit levels, insulation requirements, switching technology, protection, environmental conditions, installation configuration, maintenance access, applicable standards, and future expansion.

This switchgear selection guide explains the key technical factors to evaluate when specifying LV or MV switchgear for industrial facilities, commercial buildings, substations, utility networks, renewable energy projects, and infrastructure.

What Is Switchgear Selection?

Switchgear selection is the process of determining the appropriate electrical equipment configuration based on the requirements of a power distribution system.

Depending on the application, switchgear may incorporate:

• Circuit breakers
• Load switches
• Disconnectors
• Earthing switches
• Busbars
• Protection relays
• Current transformers
• Voltage transformers or sensors
• Metering equipment
• Control systems
• Interlocking mechanisms
• Cable compartments
• Communication equipment

The selection process should begin with the characteristics of the electrical network and then translate those requirements into equipment ratings and configurations.

A useful simplified sequence is:

System requirements → electrical calculations → equipment ratings → switchgear technology → protection and control → environmental requirements → standards → final specification

Why Correct Switchgear Selection Matters

Switchgear is a major interface between the power source and downstream electrical equipment.

Incorrect selection can result in problems such as:

• Insufficient short-circuit withstand capability
• Inadequate current capacity
• Incorrect insulation level
• Poor protection coordination
• Difficult maintenance
• Cable termination problems
• Excessive installation space
• Incompatible control systems
• Environmental degradation
• Difficult future expansion

Conversely, properly specified equipment can align the electrical installation with its intended operating conditions and maintenance strategy.

The objective is not simply to select the largest or most sophisticated switchgear. The objective is to select equipment whose ratings and functions match the actual system requirements.

1. Determine the System Voltage

The first major consideration in switchgear selection is the system voltage.

For LV systems, the equipment must be suitable for the applicable low-voltage network.

For MV systems, common distribution examples can include:

• 6.6 kV
• 10 kV
• 11 kV
• 12 kV
• 20 kV
• 22 kV
• 24 kV
• 33 kV

These are examples rather than universal voltage requirements.

The selected switchgear should have a rated voltage appropriate for the system and the applicable standard.

For MV equipment, engineers should also consider the relevant insulation characteristics, including power-frequency withstand and lightning impulse withstand where applicable.

Voltage selection should be based on the actual network rather than simply choosing the closest nominal equipment rating.

2. Determine the Continuous Current Rating

The switchgear must be capable of carrying the expected continuous current without exceeding its specified thermal limits.

Current calculations should consider:

• Normal operating load
• Maximum expected demand
• Transformer capacity
• Motor loads
• Load diversity
• Ambient conditions
• Future load growth
• Busbar configuration
• Feeder requirements

For example, an incoming switchgear section supplying several transformers may need a significantly higher continuous current rating than an individual outgoing feeder.

The current rating should also be evaluated against the complete installation rather than the circuit breaker alone.

Busbars, cable connections, terminals, disconnectors, and other current-carrying components must be appropriately rated.

3. Evaluate the Short-Circuit Level

Short-circuit capability is one of the most important parts of switchgear selection.

A switchgear assembly may experience substantial fault current during a short circuit. The equipment therefore needs appropriate capabilities for:

• Short-circuit breaking
• Short-time withstand
• Peak withstand
• Short-circuit making
• Internal fault conditions where applicable

The required value should be established from a system short-circuit study.

For example, the prospective fault current at an MV switchboard depends on factors such as:

• Utility source strength
• Transformer impedance
• Generator contribution
• Motor contribution
• Cable impedance
• Network topology

Simply selecting switchgear based on normal load current can result in an unsuitable specification.

4. Select the Appropriate Switchgear Type

Switchgear selection also requires choosing an appropriate physical and electrical technology.

Common categories include:

Air-Insulated Switchgear

Air-insulated switchgear, or AIS, uses air as the principal insulation medium around relevant components.

AIS can be used across many LV and MV applications, depending on the equipment design.

It can be suitable where installation space and environmental conditions allow the required arrangement.

Gas-Insulated Switchgear

Gas-insulated switchgear, or GIS, uses an insulating gas or gas mixture within relevant compartments.

One reason GIS may be considered is its ability to achieve compact arrangements.

However, the total installation footprint still includes cable interfaces, operating access, control equipment, and maintenance requirements.

Solid-Insulated Switchgear

Solid-insulated switchgear uses solid dielectric materials around selected primary components.

It may be considered for projects where the insulation architecture, environmental conditions, footprint, or other design requirements make this technology appropriate.

See this guide to solid insulation type switchgear for additional technical context.

RMU-Based Distribution Equipment

Ring main units can provide a compact arrangement for certain MV distribution applications.

An RMU may incorporate load switches, circuit breakers, fuses, disconnectors, earthing switches, and protection equipment depending on its configuration.

RMUs are particularly relevant to distribution substations and ring network arrangements.

5. Choose the Appropriate Circuit Breaker Technology

Circuit breaker selection is closely related to switchgear selection.

For many MV applications, vacuum circuit breakers are used because they provide switching and fault interruption within their specified ratings.

Important circuit breaker parameters include:

• Rated voltage
• Rated current
• Breaking capacity
• Making capacity
• Short-time withstand current
• Operating sequence
• Mechanical endurance
• Electrical endurance
• Control voltage
• Protection and trip requirements

For applications using VCBs, see the guide to vacuum circuit breaker letter designations.

For withdrawable MV switchgear, the chassis and withdrawal mechanism also become important. The physical arrangement must allow safe movement between service, test, and disconnected positions where such positions are provided.

6. Consider Protection Requirements

Switchgear should be selected together with the protection philosophy.

Protection may include functions such as:

• Overcurrent protection
• Earth-fault protection
• Undervoltage protection
• Overvoltage protection
• Directional protection
• Transformer protection
• Feeder protection
• Motor protection
• Differential protection where required

The actual protection functions depend on the electrical system.

Protection settings should be coordinated with upstream and downstream protective devices.

For a complex industrial or utility system, a protection coordination study can help establish appropriate settings and equipment requirements.

7. Evaluate Busbar Configuration

Busbar configuration affects system reliability, maintenance, switching flexibility, and future expansion.

Possible arrangements include:

• Single busbar
• Sectionalized single busbar
• Double busbar
• Transfer bus arrangements
• Other project-specific configurations

The correct arrangement depends on the required operating philosophy.

For example, a simple radial installation may not require the same busbar complexity as a large industrial facility or utility substation.

When specifying busbars, consider:

• Continuous current
• Short-circuit withstand
• Temperature rise
• Insulation
• Physical arrangement
• Connections
• Expansion requirements

8. Decide Between Fixed and Withdrawable Switchgear

Fixed and withdrawable designs offer different operational characteristics.

Fixed Switchgear

In fixed equipment, the main switching device remains installed in its operating position.

Potential benefits include a relatively straightforward mechanical arrangement.

However, maintenance and isolation procedures must be considered carefully.

Withdrawable Switchgear

Withdrawable equipment allows the circuit breaker or associated apparatus to move between defined positions where the design provides this functionality.

Potential benefits can include:

• Easier isolation
• Maintenance flexibility
• Reduced need to disconnect certain primary connections
• Defined service/test/disconnected positions

However, withdrawal space and mechanical interfaces must be included in the room layout.

See the guide to withdrawable chassis for vacuum circuit breakers for more information.

9. Indoor vs Outdoor Switchgear Selection

The installation environment directly affects equipment selection.

Indoor Switchgear

Indoor equipment is installed within a building or electrical room.

Selection should consider:

• Room temperature
• Humidity
• Condensation
• Ventilation
• Dust
• Cable entry
• Access
• Maintenance space
• Equipment heat dissipation

Indoor installation does not mean environmental conditions can be ignored.

Outdoor Switchgear

Outdoor equipment must be suitable for the actual environmental conditions.

Important factors can include:

• Rain
• Humidity
• Solar radiation
• Temperature extremes
• Dust
• Pollution
• Altitude
• Corrosion
• Salt exposure
• Wind and weather conditions

The equipment’s specified environmental rating should be checked against the project conditions.

10. Check Insulation Requirements

Insulation is particularly important in MV and HV switchgear.

Selection may need to consider:

• Rated insulation level
• Power-frequency withstand
• Lightning impulse withstand
• Clearance
• Creepage distance
• Pollution conditions
• Altitude
• Insulation technology

Altitude can affect insulation performance and cooling characteristics, so projects at elevated locations may require specific evaluation or derating according to the applicable requirements.

For outdoor equipment, pollution and contamination can also influence insulation performance.

11. Evaluate Cable and Termination Requirements

Cable interfaces are sometimes overlooked during switchgear procurement.

Before selecting equipment, confirm:

• Cable type
• Conductor size
• Number of cables per phase
• Cable entry direction
• Termination type
• Cable bending radius
• Screen or shield connections
• Earthing arrangement
• Available cable compartment dimensions

A switchgear lineup can meet its electrical ratings while still being difficult to install if insufficient cable space is available.

For MV systems, cable termination requirements should be established early in the project.

12. Consider Metering and Measurement

Measurement equipment can provide the information required for protection, energy management, monitoring, and control.

Depending on the application, switchgear may incorporate:

• Current transformers
• Voltage transformers
• Current sensors
• Voltage sensors
• Energy meters
• Power-quality measurement

The accuracy class and measurement characteristics should be selected according to the intended function.

Protection measurement and revenue metering, for example, can have different requirements.

13. Evaluate Automation and Communication

Modern switchgear can incorporate digital protection and communication capabilities.

Possible functions include:

• Remote switching
• Remote status monitoring
• Event recording
• Fault indication
• Energy measurement
• Protection relay communication
• SCADA integration
• Condition monitoring

When connected to a wider control network, cybersecurity and access-control requirements should also be considered.

Digital functionality should be selected according to actual operational requirements rather than simply because a product is marketed as “smart” or “digital.”

14. Check Applicable Standards

Standards are an essential part of switchgear selection.

For many MV and HV switchgear applications, the IEC 62271 series provides relevant requirements.

For LV assemblies, IEC 61439 is important for many low-voltage switchgear and controlgear assembly applications.

Other standards may apply to:

• Circuit breakers
• Transformers
• Cables
• Protection systems
• Instrument transformers
• Electrical installations
• Arc-fault performance
• Communication systems

The exact standard list should be established from the project’s jurisdiction, utility requirements, equipment type, and contract specifications.

See the International Electrotechnical Commission for the relevant standards framework.

15. Consider Environmental and Site Conditions

Electrical ratings alone do not define suitable switchgear.

Site conditions may include:

• Ambient temperature
• Altitude
• Humidity
• Dust
• Pollution
• Corrosive atmosphere
• Salt spray
• Seismic conditions
• Solar radiation
• Indoor/outdoor location

For industrial projects, chemicals, dust, moisture, or process-related contaminants may require additional attention.

The equipment specification should reflect actual site conditions rather than generic assumptions.

16. Evaluate Installation Space

The physical dimensions of the switchgear are important, but the overall installation footprint matters more than enclosure dimensions alone.

Consider:

• Front access
• Rear access where required
• Side clearances
• Cable compartments
• Breaker withdrawal space
• Maintenance access
• Door opening
• Lifting requirements
• Transport route
• Ventilation
• Future extension

Compact switchgear can reduce equipment footprint, but compactness should not be evaluated without considering operation and maintenance access.

17. Consider Maintenance Requirements

Maintenance strategy should be considered before final equipment selection.

Questions include:

• Which components require periodic inspection?
• Can circuit breakers be isolated safely?
• Is withdrawal required?
• Can cables be tested without unnecessary system interruption?
• Is spare-part availability important?
• What specialist tools are required?
• What access is needed around the equipment?
• Are condition-monitoring functions useful?

The lowest initial equipment footprint is not necessarily the same as the easiest installation to maintain.

18. Plan for Future Expansion

Electrical loads often change during the life of a facility.

Where expansion is expected, consider:

• Spare feeder cubicles
• Spare breaker positions
• Busbar capacity
• Transformer capacity
• Additional cable routes
• Room space
• Protection relay capacity
• Communication infrastructure

Designing future expansion into the initial architecture can reduce later modifications.

Switchgear Selection for Different Applications

The selection priorities can vary significantly by application.

Common Switchgear Selection Mistakes

Mistake 1: Selecting Only by Voltage

A switchgear specification cannot be completed from nominal voltage alone.

Current, fault level, insulation, protection, environment, and installation configuration also matter.

Mistake 2: Ignoring the Short-Circuit Study

Normal operating current does not tell you how equipment will perform during a fault.

The prospective short-circuit current must be evaluated before finalizing the equipment rating.

Mistake 3: Ignoring Cable Termination Space

Cable compartments can become a major installation constraint.

Always confirm the cable manufacturer’s requirements together with the switchgear interface.

Mistake 4: Choosing the Smallest Equipment

A smaller enclosure is not automatically a better selection.

The design must still provide sufficient space for operation, ventilation, cable installation, inspection, and maintenance.

Mistake 5: Ignoring Environmental Conditions

Equipment suitable for a clean indoor electrical room may not be appropriate for a humid, dusty, corrosive, or outdoor environment.

Mistake 6: Treating All Switchgear Technologies as Interchangeable

AIS, GIS, solid-insulated equipment, RMUs, fixed switchgear, and withdrawable switchgear have different characteristics.

Selection should be based on the project requirements.

Mistake 7: Forgetting Future Expansion

A switchboard with no practical expansion path may become a limitation as loads increase.

Switchgear Selection Checklist

Before finalizing a switchgear specification, confirm:

• System voltage

• Rated voltage

• Continuous current

• Short-circuit breaking capacity

• Short-time withstand current

• Peak withstand capability

• Insulation level

• Network topology

• Circuit breaker technology

• Fixed or withdrawable configuration

• Busbar arrangement

• Protection functions

• Metering requirements

• CT/VT or sensor requirements

• Cable type and termination

• Indoor or outdoor installation

• Ambient temperature

• Altitude

• Pollution level

• Corrosion exposure

• Access and maintenance requirements

• Automation and communication

• Cybersecurity requirements where applicable

• Applicable standards

• Utility requirements

• Future expansion

• Spare parts and maintenance strategy

Frequently Asked Questions About Switchgear Selection

1. What is the most important factor in switchgear selection?

There is no single factor that determines every application. System voltage, continuous current, short-circuit level, insulation, protection, environment, installation configuration, and applicable standards all need to be evaluated together.

2. How do I select MV switchgear?

Start with the system voltage, load current, short-circuit level, network topology, insulation requirements, protection philosophy, environmental conditions, cable configuration, and installation requirements. Then select the appropriate switchgear technology and configuration.

3. How do I calculate the required switchgear current rating?

The required current rating should be based on the expected continuous load and applicable design conditions, with consideration for transformer capacity, load diversity, ambient conditions, and future requirements.

4. What is short-circuit rating in switchgear?

Short-circuit ratings describe the equipment’s ability to withstand and, where applicable, interrupt fault currents under specified conditions. The relevant parameters can include breaking capacity, short-time withstand current, and peak withstand current.

5. Should I choose AIS or GIS?

The choice depends on project requirements such as available space, environmental conditions, insulation technology, maintenance strategy, cable interfaces, cost, and applicable specifications. Neither technology is universally appropriate for every project.

6. What is the difference between fixed and withdrawable switchgear?

Fixed equipment keeps the switching device in its installed position, while withdrawable designs allow the relevant apparatus to move between defined operating positions where the design provides this function. The choice affects maintenance, isolation, room layout, and mechanical complexity.

7. How does altitude affect switchgear selection?

Higher altitude can affect insulation performance and heat dissipation. The applicable equipment ratings and manufacturer requirements should therefore be checked for the actual installation altitude.

8. What protection functions should MV switchgear have?

Possible functions include overcurrent, earth fault, directional protection, voltage protection, transformer protection, motor protection, and other project-specific functions. The required functions should come from the protection study and system architecture.

9. Is outdoor switchgear different from indoor switchgear?

Yes. Outdoor equipment must be designed and rated for relevant environmental exposure such as rain, humidity, solar radiation, temperature, pollution, and corrosion. Indoor equipment operates in a more controlled environment but still requires appropriate environmental evaluation.

10. What standards should be checked during switchgear selection?

The applicable standards depend on the equipment and application. IEC 62271 is relevant to many MV/HV switchgear applications, while IEC 61439 applies to many LV switchgear and controlgear assemblies. Additional standards can apply to specific components and installations.

11. Why is protection coordination important when selecting switchgear?

Protection coordination affects breaker ratings, relay functions, current-transformer requirements, operating sequences, and system selectivity. It should therefore be considered during equipment specification rather than after procurement.

12. Should future expansion be considered?

Yes, where future load growth or additional feeders are reasonably expected. Spare cubicles, busbar capacity, cable routes, room space, and control-system capacity can all influence the initial design.

13. What information should be included in a switchgear RFQ?

A technical RFQ should typically identify the system voltage, current requirements, short-circuit level, installation environment, number and type of feeders, protection requirements, cable interfaces, control voltage, communication requirements, applicable standards, and project-specific specifications.

Final Switchgear Selection Strategy

A reliable switchgear selection process connects the electrical system study with the equipment specification.

Start with the network:

Voltage → load current → short-circuit level → topology → protection

Then evaluate the equipment:

Switchgear technology → breaker/switching technology → insulation → busbars → cable interfaces → control and monitoring

Finally, evaluate the installation:

Environment → space → maintenance → safety → standards → future expansion

This approach helps engineers and procurement teams avoid selecting equipment based on a single parameter.

The appropriate switchgear is the equipment whose electrical ratings, construction, protection, environmental capability, interfaces, and operating features align with the complete project requirement.