4.16 kV, 13.8 kV, and 34.5 kV Switchgear: Which Voltage Class You Need

The voltage written beside a bus on a one-line is normally its nominal system voltage. A switchgear nameplate gives a rated maximum voltage, meaning a class of equipment designed and tested for a stated upper operating voltage. A request for “13.8 kV switchgear” describes the system, but the equipment offered is commonly identified as 15 kV class. Schneider Electric’s system-voltage table lists 13,800 V as a nominal system voltage; IEEE C37.20.2-2025 describes the rated maximum voltage levels covered by the metal-clad standard.

Do not assume the equipment-class number is the voltage that will always appear on the bus. A 15 kV class lineup can serve a 13.8 kV nominal system when all other ratings fit. The reverse reasoning fails: a 13.8 kV bus does not make a 15 kV class breaker suitable if its interrupting rating, insulation level, or current rating is inadequate. The class is one entry in the technical check, not the conclusion.

Basic impulse insulation level, or BIL, is the specified impulse-withstand capability associated with the insulation design. It is expressed in kV peak and is different from the steady AC voltage. Eaton’s metal-enclosed guide pairs rated maximum voltage with impulse withstand values in product tables. A class label alone may omit an important distinction: manufacturer examples show different BIL choices at the same rated maximum class. Ask for the actual assembly and breaker nameplates.

The nominal system itself may have allowable operating variation. Schneider Electric points readers to the serving utility when service voltage conditions are uncertain. Its voltage guide is a reminder to check the utility’s actual supply and the project’s equipment-insulation basis before treating a nominal drawing number as the worst operating case.

4.16 kV can be served by 4.76 kV class gear when that product’s ratings and project requirements fit. A project may instead standardize on a higher 15 kV class family, but 15 kV is not the minimum class the nominal voltage demands. Eaton’s switchgear rating table shows a 4.76 kV, 60 kV BIL product; Schneider Electric’s product table also lists 4.76 kV class equipment. A site with both 4.16 and 13.8 kV buses might choose a common product family for spares, but the decision is specific to its design.

13.8 kV fits under the 15 kV rated maximum class commonly used in North American MV switchgear. The typical BIL shown in the cited Eaton product tables is 95 kV. That does not specify the main bus amperes or the breaker fault duty. For a 13.8 kV feeder, ask for the 15 kV class assembly rating plus those independent ratings. A 15 kV class label cannot resolve whether a given feeder breaker will clear the site’s calculated fault.

34.5 kV is a nominal system voltage that calls for equipment rated above it; 38 kV class appears in the North American product tables. Eaton’s metal-enclosed guide shows 38 kV with 150 kV impulse withstand for one family, while its comparison guide shows that another metal-clad configuration may have a different BIL. Eaton’s product comparison illustrates why a single “38 kV equals 150 kV BIL” rule should not replace a submittal check. The class gets you to the right candidate family; the exact insulation duty is verified on the offered gear.

A 24.94 kV nominal system is another useful example. It sits below a 27 kV rated maximum class in the OEM tables. If a gas-insulated product is rated only 24 kV, the fact that it is described as “medium voltage” does not make it suitable for 24.94 kV service. Compare the actual maximum equipment voltage with the utility’s operating range before comparing footprints or insulation media.

A 4.16 kV bus is below both 4.76 kV and 15 kV rated maximum equipment voltages, but choosing a class involves more than comparing two numbers. A dedicated 4.76 kV lineup can be a sensible fit for a system that will remain 4.16 kV. A higher-class lineup may be chosen when an owner wants a common equipment family across multiple buses. Neither preference can be inferred from a search query alone.

Compare the complete lineup and breaker combination. Does the 4.76 kV family have the required bus amperes, interrupting rating, arc classification, and control options? Does the 15 kV family fit the room and cable arrangement? IEEE C37.20.2 lists the broad voltage and bus range of the metal-clad standard, but those standard ranges do not prove a specific manufacturer’s offering. Ask for a product drawing and tested ratings at the requested class.

The higher-class choice also has no automatic “future proof” guarantee. A later conversion from 4.16 to 13.8 kV would affect transformer ratios, cables, motors, instrument transformers, surge arresters, relay settings, and clearances throughout the system. Merely installing 15 kV class switchgear at the beginning does not authorize energizing the whole network at 13.8 kV later. The decision must follow an engineered conversion plan.

Keep the two voltages on every schedule: “4.16 kV nominal system; offered 4.76 kV class gear” or “4.16 kV nominal system; offered 15 kV class gear.” That simple wording prevents a reviewer from reading the nameplate class as a different utility service voltage.

BIL deals with a short-duration impulse, not the continuous bus current and not the circuit-breaker fault current. A 15 kV class, 95 kV BIL lineup still needs a separate ampere rating and separate interrupting and withstand ratings. That distinction is visible in Eaton’s switch and bus tables, which put voltage, impulse withstand, load current, and fault-duty columns side by side. Copying one column into another is a specification error.

Product literature is not perfectly uniform at the intermediate class. A Schneider Electric metering drawing lists 8.25 kV with 75 kV BIL, while a Schneider Electric primary-distribution product table and Eaton’s metal-clad comparison show 8.25 kV product examples with 95 kV BIL. The safe request is therefore “state the required BIL and provide the offered tested value,” especially for replacement equipment that must match an existing station’s insulation coordination. The table above records both examples rather than pretending one is universal.

At 38 kV, a similar caution applies. A cited Eaton switch family uses 150 kV; its comparison of a metal-clad family lists a different 38 kV BIL. The assembly, connected transformer, cable terminations, and surge-arrester choice need to be reviewed as a system. Do not infer that the highest BIL number on one brochure automatically makes the whole installation suitable.

When equipment is used or surplus, look for the actual BIL marking and the complete test or manufacturer data. An unlabeled cubicle that visually resembles a 15 kV section cannot be accepted as 15 kV, 95 kV BIL equipment without evidence. The answer affects both safety and compatibility with upstream equipment.

After voltage and insulation, compare the current path. The main bus must carry the load in both normal and planned transfer states. Each feeder breaker or switch needs its own continuous rating. IEEE’s metal-clad standard abstract lists several main-bus ratings, but it does not imply every rating is available for a chosen voltage, enclosure, or arc design. A 38 kV class lineup and a 15 kV class lineup with the same bus current may have very different physical arrangements.

Short-circuit duty is local to each equipment position. A strong utility source can produce a high fault current even when the connected load is small. IEEE C37.04 treats continuous current, insulation, and short-circuit current as separate breaker ratings. An RFQ with only “15 kV class, 2000 A” leaves out the breaker interrupting duty and the assembly short-time withstand. Attach the fault-study result and state the X/R or asymmetry basis used for making-duty checks.

Close-and-latch numbers need their unit basis. ABB’s breaker application guide gives approximately 1.55 times rated short-circuit current in rms asymmetrical terms and 2.6 times in peak terms for the cited K = 1.0 case. If a spreadsheet has a “close and latch” cell with no peak or rms label, a factor can be silently misapplied. For the selected product, use its own rating data and the applicable standard edition.

The rating check must also include the assembled lineup. A breaker may have a fault rating that exceeds the bus or switchgear assembly’s short-time rating. Conversely, a high-rated bus does not upgrade a lower-rated feeder breaker. Record both assembly and device nameplates before concluding that an existing lineup meets the study.

Write the system voltage served first, then the offered or required equipment class. A useful opening is: “13.8 kV nominal system; 15 kV rated maximum metal-clad switchgear; 95 kV BIL; main bus, feeders, and short-circuit duty per attached one-line and study.” This phrasing shows what the site operates and what the equipment must withstand. It also makes a misquoted 24 kV product on a 24.94 kV system easier to catch.

Include the construction standard. IEEE C37.20.2 is the metal-clad assembly standard; IEEE C37.20.3 is the metal-enclosed interrupter standard. The metal-clad versus metal-enclosed guide covers the construction choice. A class and BIL row cannot tell the supplier whether the owner expects drawout breakers or fused switches.

Add the operating details that affect a real offer: source grounding, frequency, indoor or outdoor location, cable entry, main-tie-main or radial topology, control power, relay and metering schedule, and any internal-arc requirement. If the equipment is intended to be close-coupled to a transformer, attach the unit-substation interface drawing and transformer data. A voltage-class decision is necessary, but it is only one layer of the package.

Pantheon’s electrical catalog can start a quote request. State the nominal system voltage, equipment class, and BIL with the one-line and fault study so we can check sourceable configurations. Ask the project engineer to review any offered substitution against the full duty, including current and interrupting ratings.

Calling 4.16 kV a mandatory 15 kV-class application. The nominal system fits 4.76 kV class equipment in cited OEM tables. A higher class may be a project choice, but it should be stated as such.

Assuming one BIL per class without reading the product data. The cited 8.25 kV examples include both 75 and 95 kV BIL; Eaton’s comparison also shows a higher 38 kV metal-clad example than its interrupter-switch example. Confirm the offered assembly’s tested value.

Treating “35 kV” as an equipment nameplate. It is often shorthand for a 34.5 kV nominal system. State 34.5 kV system voltage and the 38 kV equipment class separately.

Using rated maximum voltage as a proxy for fault duty. Voltage, continuous current, BIL, interrupting current, and short-time withstand answer different questions. Put each on its own line in the comparison sheet.