Switchgear Specification: Ratings, Requirements & Selection Guide

A switchgear specification defines the electrical, mechanical, environmental, protection, control, and testing requirements that switchgear must meet for a particular power distribution application. A well-prepared specification helps engineers, contractors, utilities, and purchasers compare equipment consistently and ensures the selected switchgear is suitable for the system.

The specification may cover medium-voltage or low-voltage equipment, depending on the project. For MV applications, important parameters commonly include rated voltage, rated current, short-circuit withstand capability, circuit-breaker characteristics, insulation requirements, protection functions, enclosure design, installation conditions, and applicable standards.

This guide explains the major elements to consider when preparing or reviewing a switchgear specification.

What Is a Switchgear Specification?

A switchgear specification is a technical document that describes the required characteristics and performance of electrical switchgear.

It can be used as:

• A project design requirement
• A procurement document
• An equipment comparison checklist
• A basis for supplier quotations
• A reference for engineering approval
• A framework for inspection and testing

A specification should describe the actual requirements of the electrical system rather than simply naming a preferred product.

For example, specifying only “12 kV switchgear” is rarely sufficient. The complete requirement may also need to define current rating, fault level, insulation requirements, breaker type, protection scheme, enclosure, environmental conditions, cable arrangement, control voltage, communications, and testing.

For equipment options, see the switchgear products available for different applications.

Key Information in a Switchgear Specification

Although formats vary between projects, a comprehensive specification normally includes several groups of information.

The exact requirements should be established from the project electrical design and applicable standards.

Start With the Electrical System Requirements

The switchgear specification should begin with the electrical system rather than the equipment catalog.

Important information includes:

• Nominal system voltage
• Maximum operating voltage
• Frequency
• System fault level
• Maximum load current
• Transformer ratings
• Number of incoming and outgoing feeders
• Earthing arrangement
• Required protection philosophy
• Utility or grid connection requirements

These parameters establish the foundation for equipment selection.

For example, a switchgear lineup connected to a distribution transformer may have very different requirements from switchgear used at a renewable-energy collector substation or industrial motor-control application.

Voltage and Insulation Ratings

Voltage is one of the first parameters considered in a switchgear specification.

For medium-voltage systems, common equipment classes include 12 kV, 24 kV, and 36 kV, although the appropriate rating depends on the actual system voltage, applicable standards, and project requirements.

The specification may distinguish between:

• Nominal system voltage
• Rated voltage
• Maximum system voltage
• Power-frequency withstand voltage
• Lightning impulse withstand voltage

Insulation coordination is particularly important because switchgear must withstand normal operating conditions as well as expected transient overvoltages.

The equipment rating should therefore be selected according to the system and applicable technical requirements rather than simply matching the nominal voltage.

Current Ratings

The rated current represents the continuous current the equipment is designed to carry under specified conditions.

A switchgear specification may identify current ratings for:

• Main busbars
• Incoming feeders
• Outgoing feeders
• Circuit breakers
• Disconnectors
• Load switches

The required rating should account for the expected operating load and the system design.

Engineers may also need to consider future expansion, transformer capacity, parallel feeders, load growth, and installation conditions.

Selecting a current rating solely from today’s measured load can create unnecessary limitations later.

Short-Circuit and Withstand Ratings

Fault-current capability is one of the most important parts of a switchgear specification.

The equipment may need to demonstrate adequate capability for:

• Short-time withstand current
• Peak withstand current
• Short-circuit breaking current
• Making current
• Internal arc performance where specified

The required fault rating should be based on the calculated short-circuit level at the installation point.

For example, a switchgear panel installed near a large transformer may experience a substantially different prospective fault current from equipment installed farther down a distribution network.

The specification should therefore connect the equipment rating to the project’s short-circuit study.

Switchgear Type and Technology

A specification should clearly identify the required switchgear configuration and technology.

Potential options include:

Air-Insulated Switchgear

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

AIS can be appropriate where physical space, accessibility, configuration, and project requirements support this arrangement.

Gas-Insulated Switchgear

GIS uses an insulating gas within an enclosed system. The specification should identify the required insulating medium and any applicable environmental or regulatory requirements.

Where SF6 technology is considered, the project specification should account for the relevant requirements governing SF6 equipment and handling.

Solid-Insulated Switchgear

Solid-insulated designs use solid dielectric materials around selected electrical components.

When evaluating this technology, the specification should address insulation performance, construction, environmental conditions, maintainability, and applicable testing.

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

SF6-Free Switchgear

Projects seeking to reduce reliance on SF6 may specify alternative insulation technologies.

However, an SF6-free requirement should still be accompanied by the required electrical ratings, insulation performance, fault capability, environmental conditions, and applicable standards.

The phrase “SF6-free” alone is not a complete technical specification.

Circuit Breaker Specification

The circuit breaker is a central part of many switchgear assemblies.

For medium-voltage distribution systems, vacuum circuit breakers are widely used. A specification may need to define:

• Rated voltage
• Rated current
• Short-circuit breaking capacity
• Making capacity
• Operating sequence
• Mechanical endurance
• Electrical endurance
• Opening and closing times
• Control voltage
• Trip and close coil requirements
• Auxiliary contacts
• Motorized mechanism
• Undervoltage or other optional releases

For applications using vacuum circuit breakers, understanding model designations can help engineers interpret manufacturer documentation. See the VCB model letters guide.

The specification should also state whether the breaker is fixed-mounted or withdrawable and define the required mechanical and electrical interlocks.

Protection and Control Requirements

Modern switchgear is more than a collection of switching devices. Protection and control functions can significantly affect the overall specification.

Depending on the application, requirements may include:

• Overcurrent protection
• Earth-fault protection
• Undervoltage protection
• Overvoltage protection
• Directional protection
• Differential protection
• Motor protection
• Transformer protection
• Feeder protection
• Automatic transfer
• Reclosing functions
• Remote control
• Condition monitoring

The specification should identify required protection functions and their interfaces rather than simply stating “protection relay included.”

If the switchgear will form part of a digital substation or automated distribution system, communication and control requirements should also be defined.

Metering and Monitoring

A detailed switchgear specification may include requirements for electrical measurement and equipment monitoring.

Potential requirements include:

• Current transformers
• Voltage transformers
• Voltage sensors
• Energy meters
• Power-quality monitoring
• Temperature monitoring
• Partial-discharge monitoring
• Breaker condition monitoring
• Local indication
• Remote status indication

The required accuracy class and measurement performance should be specified according to the purpose of the measurement.

Protection CT requirements, for example, can differ significantly from metering CT requirements.

Enclosure and Environmental Requirements

The installation environment has a direct effect on the switchgear specification.

The document may need to identify:

• Indoor or outdoor installation
• Ambient temperature
• Relative humidity
• Altitude
• Pollution level
• Dust
• Moisture
• Corrosive atmosphere
• Solar exposure
• Seismic requirements
• Special environmental conditions

The enclosure and protection level should be selected for the actual installation environment.

There is no single IP rating that is universally correct for every switchgear installation. The appropriate enclosure requirements depend on whether the equipment is installed indoors, outdoors, in an industrial environment, or in another specialized location.

Layout, Cable Entry and Maintenance Access

Physical design is another important part of a complete switchgear specification.

The document should consider:

• Overall dimensions
• Panel arrangement
• Busbar configuration
• Cable compartment
• Cable entry direction
• Terminal arrangement
• Front or rear access
• Breaker extraction space
• Maintenance access
• Lifting provisions
• Installation clearances

For withdrawable switchgear, the movement and extraction path of the breaker should be considered during room planning.

A technically correct switchgear lineup can still create installation problems if the specification ignores access, cable bending space, or maintenance requirements.

Standards and Testing

The switchgear specification should identify the applicable standards and project requirements.

For medium-voltage switchgear, relevant parts of the IEC 62271 series may apply depending on the equipment type and application.

For low-voltage switchgear and assemblies, relevant parts of the IEC 61439 series may apply.

The specification should also identify required inspection and testing procedures.

These may include:

• Routine tests
• Type-test requirements
• Factory acceptance testing
• Mechanical operation tests
• Dielectric tests
• Wiring verification
• Protection relay testing
• Functional testing
• Visual and dimensional inspection

See the IEC official website for information about IEC standards and publications.

For vacuum circuit breakers, additional technical details can be reviewed in this guide to VCB letter designations.

Switchgear Specification for Renewable Energy and BESS

Renewable-energy projects can introduce additional requirements into a switchgear specification.

Solar Plants

Solar plants commonly require switchgear for collection, transformation, protection, and grid interconnection.

The specification may need to address:

• Transformer connections
• Medium-voltage collector feeders
• Grid interconnection
• Protection coordination
• Remote monitoring
• Outdoor environmental conditions

Wind Farms

Wind projects can require switchgear across turbine collection networks and substations.

Special attention may be needed for:

• Collector voltage
• Fault levels
• Cable systems
• Remote operation
• Environmental conditions
• Substation integration

Battery Energy Storage Systems

BESS projects can involve multiple electrical interfaces between batteries, power-conversion equipment, transformers, and the grid.

The switchgear specification may therefore need to coordinate with:

• Power conversion systems
• Step-up transformers
• Protection relays
• Energy-management systems
• Grid protection
• Emergency isolation requirements
• Remote monitoring and control

The specification should be developed around the complete electrical architecture rather than selecting the switchgear independently.

Common Switchgear Specification Mistakes

Several specification problems can lead to unsuitable equipment or unnecessary procurement complications.

1. Specifying only the voltage

“12 kV switchgear” does not define the complete equipment requirement.

2. Ignoring the fault level

The short-circuit requirement must be established from the electrical system study.

3. Forgetting the installation environment

Temperature, altitude, pollution, moisture, and enclosure requirements can affect equipment suitability.

4. Leaving protection requirements vague

Protection functions, CTs, VTs, relays, interlocks, and communication interfaces should be clearly defined.

5. Ignoring future expansion

Where appropriate, the specification should consider spare feeders, busbar capacity, physical space, and future load requirements.

6. Treating standards as an afterthought

Applicable standards should be established during specification development, not after equipment has already been selected.

7. Over-specifying without a technical reason

Excessive requirements can increase cost and reduce the available supplier base without improving the actual system.

Switchgear Specification Checklist

Before issuing a purchase specification, review the following checklist:

This checklist provides a practical starting point, but the final specification should reflect the project’s electrical calculations, drawings, applicable standards, and contractual requirements.

Frequently Asked Questions

What should a switchgear specification include?

A switchgear specification should normally include electrical ratings, fault-current requirements, insulation levels, switchgear technology, circuit-breaker requirements, protection and control, enclosure and environmental conditions, installation requirements, applicable standards, testing, and documentation.

What is the most important switchgear rating?

There is no single rating that is always the most important. Voltage, continuous current, short-circuit capability, insulation performance, and environmental suitability all need to match the application.

How do I specify 12 kV switchgear?

Start with the actual system voltage and then define rated voltage, continuous current, short-circuit rating, insulation levels, breaker type, protection, control, enclosure, cable arrangement, environmental conditions, standards, and testing requirements.

What standard applies to MV switchgear?

Relevant parts of the IEC 62271 series apply to many medium- and high-voltage switchgear and controlgear products. The exact applicable standard depends on the equipment and application.

Should switchgear be AIS or GIS?

The choice depends on space, environmental conditions, insulation technology, maintenance strategy, project requirements, and cost. AIS and GIS should be compared against the complete application rather than using a single technology as a universal answer.

What should be specified for a vacuum circuit breaker?

Typical requirements include rated voltage, rated current, short-circuit breaking capacity, making capacity, operating sequence, endurance, control voltage, auxiliary contacts, operating mechanism, and required protection and interlocking functions.

Does switchgear specification include protection relays?

It can and often should when the switchgear package includes an integrated protection and control system. The specification should clearly identify relay functions, interfaces, CT/VT requirements, communications, and testing responsibilities.

What environmental conditions should be included?

Consider ambient temperature, altitude, humidity, pollution, dust, moisture, corrosive conditions, outdoor exposure, seismic requirements, and other conditions relevant to the installation.

Should future expansion be included in the specification?

Where future expansion is expected, it can be useful to specify provisions such as spare feeder positions, capacity margins, extension arrangements, or physical space. The appropriate provision depends on the project plan.

What is the difference between a technical specification and a datasheet?

A datasheet generally summarizes equipment characteristics. A technical specification defines the complete project requirements, including performance, configuration, standards, testing, documentation, and other contractual requirements.

Can one switchgear specification be used for every project?

No. A standard specification template can provide a useful starting point, but project-specific electrical ratings, fault levels, protection requirements, environmental conditions, installation arrangements, and standards must be evaluated for each application.

How should switchgear suppliers be compared?

Compare suppliers against the same technical requirements. Review electrical ratings, compliance, test documentation, protection and control features, mechanical configuration, environmental suitability, manufacturing quality, documentation, delivery requirements, and lifecycle considerations.

Conclusion

A strong switchgear specification converts the needs of an electrical system into clear and verifiable equipment requirements.

The most important areas include:

• Voltage and insulation ratings
• Continuous current
• Short-circuit capability
• Switchgear technology
• Circuit-breaker performance
• Protection and control
• Metering and monitoring
• Environmental conditions
• Physical layout and maintenance access
• Applicable standards
• Testing and documentation

For modern applications such as renewable-energy plants, BESS installations, digital substations, and automated distribution networks, the specification may also need to address remote control, communications, condition monitoring, and integration with other electrical systems.

The goal is not to create the longest possible specification. It is to create a clear, technically justified, measurable specification that ensures the selected switchgear is suitable for its intended duty.