How to Identify Existing Switchgear: Nameplates, One-Lines, and Drawings

Identifying existing switchgear is usually more complicated than reading a single nameplate.

A switchgear assembly can contain multiple sections, breakers, switches, fuses, bus, controls, protection relays, instrument transformers, and other equipment. The assembly nameplate tells you important ratings, but it may not tell you everything needed to source a replacement lineup, expansion section, or compatible circuit breaker.

For sourcing, the best identification package usually combines:

1. The switchgear assembly nameplate
2. Breaker or switching-device nameplates
3. A one-line diagram
4. Shop or lineup drawings
5. Clear photos of the equipment
6. Manufacturer, model/family, and section information

If all you have is a photo and a nameplate, send those first. You do not need to reconstruct the entire system before starting.

Step 1: Identify the Equipment Family

Before reading individual ratings, determine what kind of equipment you are looking at.

Common GridGear sourcing families include:

• Medium-Voltage Metal-Clad Switchgear
• Medium-Voltage Metal-Enclosed Switchgear
• Pad-Mounted Switchgear
• Generator Paralleling Switchgear
• Automatic Transfer Switches
• Automatic Transfer Switchgear
• Low-Voltage Switchgear
• Switchboards
• Replacement Medium-Voltage Circuit Breakers

This matters because different equipment families use different device types and different sourcing information.

For example:

• Metal-clad switchgear commonly centers on drawout circuit breakers.
• Metal-enclosed switchgear may use fused load-interrupter switches, breakers, or other devices.
• Pad-mounted switchgear is often described by ways, interrupters, insulation medium, and radial/loop configuration.
• Replacement breaker sourcing can depend heavily on the exact cubicle and racking interface.

If the equipment family is unclear, photos of the full lineup are useful.

Step 2: Photograph the Assembly Nameplate

Look for a nameplate on the overall switchgear assembly or lineup.

The exact information varies by manufacturer and equipment type, but common assembly ratings can include:

• Manufacturer
• Model or equipment type
• Serial, project, or order number
• Rated voltage or voltage class
• Continuous-current or main-bus rating
• Short-circuit rating
• Frequency
• Number of phases/wires on some equipment
• Construction type
• Manufacturing year
• Standard or instruction-manual references

On medium-voltage equipment, additional insulation or withstand ratings may be shown or available in project documentation.

Take a clear photo of the entire plate rather than transcribing only one or two ratings.

Step 3: Separate Voltage Class From Actual System Voltage

One of the easiest mistakes in switchgear identification is to confuse the equipment voltage class or rated maximum voltage with the actual system operating voltage.

A lineup might belong to a 15 kV class while operating on a 12.47 kV, 13.2 kV, or 13.8 kV system.

The assembly nameplate may help identify the equipment rating. The one-line diagram or project drawings often make the actual system voltage clearer.

For sourcing, capture both if known.

Step 4: Find the Bus or Continuous-Current Rating

Switchgear is rated for a continuous current.

Depending on the equipment, this may be labeled as:

• Main bus rating
• Rated current
• Continuous current
• Ampere rating

Examples in medium-voltage systems can include 1200 A, 2000 A, 3000 A, or 4000 A, although available ratings depend on equipment family and design.

Do not assume the breaker current rating and the lineup bus rating are always the same.

Step 5: Find the Short-Circuit / Interrupting Information

Switchgear and circuit breakers have short-circuit-related ratings that determine what fault duty the equipment is designed to withstand or interrupt.

The terminology changes by equipment type.

You may see:

• Short-circuit current
• Short-time withstand current
• Interrupting current
• Fault-interrupting rating
• Withstand and closing rating on transfer equipment

For metal-clad switchgear, the breaker interrupting capability is particularly important.

For metal-enclosed or pad-mounted equipment, the applicable rating and device terminology may be different.

Do not combine different ratings into a single guessed "kA rating." Photograph the plate and device labels if the terminology is unclear.

Step 6: Capture BIL or Insulation Ratings When Available

Medium-voltage equipment may have a BIL or other dielectric/impulse withstand rating associated with its insulation system.

BIL is not the same thing as operating voltage.

IEEE medium-voltage switchgear standards include dielectric withstand and insulation requirements as part of the equipment rating structure.

If BIL or other insulation-withstand information is on the plate, drawings, or specification, include it in the sourcing package.

Step 7: Photograph the Breaker or Primary Switching Device

The lineup nameplate identifies the assembly. The breaker or switch nameplate identifies the device installed inside it.

For medium-voltage circuit breakers, useful information can include:

• Manufacturer
• Breaker type or model
• Rated maximum voltage
• Continuous-current rating
• Interrupting / short-circuit rating
• Insulation capability
• Control-power or coil voltage
• Mechanism or design family
• Serial number

IEEE C37.04 establishes the rating structure for AC high-voltage circuit breakers above 1000 V, including continuous current, insulation capability, and short-circuit current.

For replacement breaker sourcing, a clear breaker nameplate is often essential.

Step 8: Do Not Treat a Breaker Nameplate as Proof of Cubicle Compatibility

Two breakers can have similar electrical ratings and still not fit the same switchgear cubicle.

Replacement-breaker compatibility may depend on:

• Racking mechanism
• Truck or cradle
• Primary stab arrangement
• Secondary disconnect
• Pole spacing
• Interlocks
• Control voltage
• Cell dimensions
• Manufacturer-specific modifications
• Retrofit or retrofill design

That is why replacement medium-voltage breaker sourcing often requires both the breaker identification and the switchgear/cubicle information.

Electrical ratings are only part of the match.

Step 9: Use the One-Line Diagram to Understand the System

A one-line diagram is a simplified drawing showing how the major electrical equipment is connected.

For switchgear sourcing, a one-line can help answer questions the nameplate cannot, such as:

• What feeds the lineup?
• What is the actual system voltage?
• Is there one main or multiple mains?
• Is there a tie breaker?
• Is the arrangement Main-Tie-Main?
• How many feeders are involved?
• Is the switchgear connected to a transformer?
• Are generators or alternate sources involved?
• Is automatic transfer or paralleling part of the system?
• What devices or protective functions are shown?

A one-line is especially useful when the buyer says, "I need another section like this," but the exact system arrangement is unclear.

Step 10: Use Shop / Lineup Drawings for Physical Matching

Shop drawings or as-built drawings can provide physical and construction information that a nameplate does not.

Useful details may include:

• Overall lineup length
• Section widths and heights
• Section sequence
• Bus ratings
• Bus transitions
• Cable-entry direction
• Breaker cell arrangement
• Main / tie / feeder section positions
• Throat or transformer connections
• Shipping splits
• Control compartments
• Door and access arrangement
• Foundation details
• Manufacturer drawing numbers

For an expansion section, replacement cubicle, or equipment that must physically match an existing lineup, these drawings can become critical.

Step 11: Take Photos of the Full Lineup

Do not photograph only the nameplate.

Useful photos include:

• Full front of the lineup
• Full rear, if safely accessible
• Manufacturer labels
• Assembly nameplate
• Breaker or device nameplates
• Section labels
• Main, tie, and feeder designations
• Bus-transition or throat areas
• Cable-entry arrangement
• Exterior condition
• Any unusual modifications

Photos help establish context and can reveal whether the equipment identification has been interpreted correctly.

Safety note

Do not open energized compartments, defeat interlocks, remove protective barriers, or enter restricted electrical spaces just to obtain sourcing photos.

Use existing external labels and drawings where possible. Internal inspection or energized-equipment access should be performed only under the site's electrical-safety procedures by appropriately qualified personnel.

What Information Matters by Equipment Type?

Medium-Voltage Metal-Clad Switchgear

Prioritize:

• Manufacturer and lineup family
• Voltage class
• Actual system voltage
• Bus rating
• Breaker interrupting rating
• BIL
• Breaker type
• Lineup configuration
• Section count
• Indoor/outdoor construction
• One-line and lineup drawing

IEEE C37.20.2 covers metal-clad switchgear containing drawout electrically operated circuit breakers and defines requirements for ratings, construction, insulation, testing, and application.

Medium-Voltage Metal-Enclosed Switchgear

Prioritize:

• Manufacturer and family
• Voltage class / system voltage
• Continuous-current rating
• Short-circuit rating
• BIL
• Primary device type
• Fuse information if applicable
• Lineup configuration
• Enclosure
• One-line and drawings

IEEE C37.20.3 covers metal-enclosed interrupter switchgear containing devices that can include interrupter switches, selector switches, power fuses, circuit breakers, metering, and protective equipment.

Pad-Mounted Switchgear

Prioritize:

• Manufacturer and model
• Voltage
• Continuous current
• Fault-interrupting rating
• BIL if applicable
• Number of ways
• Switch / interrupter type
• Insulation medium
• Radial / loop / sectionalizing configuration
• Front or operating configuration
• Photos and diagram

Generator Paralleling Switchgear

Prioritize:

• System voltage
• Bus rating
• Short-circuit rating
• Generator count
• Generator capacity
• Utility source count
• Main/tie/generator arrangement
• One-line
• Synchronizing / control architecture
• Manufacturer drawings

ATS / Automatic Transfer Switchgear

Prioritize:

• Ampere or bus rating
• System voltage
• Number and type of sources
• Transition type
• Poles for ATS equipment
• Withstand/closing or short-circuit rating
• Bypass-isolation if applicable
• Transfer scheme
• One-line and control drawings

Replacement Medium-Voltage Circuit Breaker

Prioritize:

• Switchgear manufacturer
• Switchgear family/model
• Breaker manufacturer/model
• Breaker nameplate
• Voltage and current ratings
• Interrupting rating
• Cubicle/cell identification
• Racking mechanism
• Control voltage
• Photos of the breaker and cell
• Existing switchgear drawings

For a replacement breaker, what the breaker must fit can be as important as the breaker ratings themselves.

Different Sourcing Jobs Need Different Identification Packages

Replacing an entire lineup

Start with:

• Assembly nameplate
• One-line
• Lineup drawings
• Electrical ratings
• Section configuration
• Physical dimensions
• Project timing and location

Adding or replacing a section

Start with:

• Existing manufacturer and lineup family
• Adjacent-section drawings
• Bus rating and geometry
• Section dimensions
• Transition details
• One-line
• Photos

Replacing a circuit breaker

Start with:

• Breaker nameplate
• Existing switchgear manufacturer/family
• Cubicle identification
• Racking/cell information
• Electrical ratings
• Control voltage
• Photos and drawings

Identifying unknown equipment

Start with:

• Full equipment photos
• Every visible manufacturer/nameplate label
• One-line
• Old quote or specification
• Drawings
• Breaker/device labels

GridGear can begin with partial information and narrow the requirement from there.

What If the Drawings Are Missing?

Do not assume the project is blocked.

Send what you have:

• Assembly nameplate
• Breaker nameplate
• Photos
• Manufacturer
• Model/family
• Section labels
• Old maintenance records
• Old quote
• Partial one-line
• Existing equipment schedule

The first goal is to establish the equipment family and electrical identity. Additional compatibility diligence can follow if a promising sourcing option is found.

Need Help Identifying Existing Switchgear?

Send GridGear the nameplates, one-line, lineup drawings, breaker information, or photos you have.

We can use that information to help identify the equipment and narrow the sourcing requirement before you spend time reconstructing every technical field.

Request a Switchgear Quote

Technical References

This resource is GridGear-authored educational content informed by industry standards and technical references.

Relevant standards include:

• IEEE C37.20.2 — Metal-Clad Switchgear
• IEEE C37.20.3 — Metal-Enclosed Interrupter Switchgear
• IEEE C37.04 — Ratings and Requirements for AC High-Voltage Circuit Breakers Above 1000 V

Different switchgear families may fall under additional IEEE, ANSI, NEMA, or UL requirements. Project drawings and manufacturer documentation remain important because standards define equipment classes and ratings but do not establish whether a particular used or replacement component will physically fit an existing installation.

This guide is intended to help identify sourcing information. Formal engineering, protection, installation, and equipment-compatibility decisions should use the applicable project specifications, drawings, standards, manufacturer data, and qualified technical review.