Metal-Clad vs Metal-Enclosed Switchgear

“Metal-enclosed” describes a broad family of switchgear assemblies housed in metal. “Metal-clad” names a more specific form of metal-enclosed switchgear with drawout breakers and grounded barriers separating major components. In medium-voltage North American specifications, IEEE C37.20.2-2025 is the metal-clad standard and IEEE C37.20.3-2023 is the metal-enclosed interrupter-switchgear standard. A request that uses the two words interchangeably can produce equipment with different operating and maintenance arrangements.

Think of a 13.8 kV transformer feeder. One design might use a fixed load-interrupter switch and fuses in a metal-enclosed assembly. Another might use a drawout vacuum breaker, relays, and separate grounded compartments in metal-clad gear. Both can connect the transformer to the distribution system, but the owner’s protection study and maintenance sequence determine which arrangement is suitable. Eaton’s comparison of two product families makes the device and construction differences concrete.

Avoid turning either standard into a quality slogan. IEEE C37.20.3 now explicitly includes assemblies that may contain interrupter switches, selector switches, power fuses, circuit breakers, controls, metering, and protection. Its scope is broader than “a fused switch in a box.” Conversely, a metal-clad designation does not establish an internal-arc rating or a particular relay scheme. Read the offered assembly data and test designation.

The low-voltage phrase “metal-enclosed power circuit-breaker switchgear” is another source of confusion. It refers to low-voltage equipment under C37.20.1, a separate standard from either MV category. If the one-line is 480 V, do not assume a C37.20.2 or C37.20.3 reference is the right one merely because the words sound familiar.

The current IEEE C37.20.2 abstract identifies drawout electrically operated circuit breakers and compartments that isolate instrumentation, main bus, and incoming and outgoing connections with grounded metal barriers. That is the key physical difference a reader should picture. The breaker is a removable device in a cell; the bus and cables are in other compartments. The assembly also contains control, metering, and protective devices as required by its application.

Schneider Electric’s metal-clad equipment guide describes the familiar detailed arrangement: drawout primary devices, separate grounded metal compartments, insulated bus, shutters, and interlocks. These features need to be examined in the actual product manual and standard edition. For example, a breaker in its disconnected position may be electrically separated from the primary stabs, but an adjacent bus compartment can remain energized. A shutter is one barrier in an operating procedure, not proof that all conductors in the cubicle are dead.

Drawout construction changes how maintenance can be planned. A breaker can be removed from its cell for inspection or replacement under the specified procedure, while other circuits may remain in service. That does not mean a worker may reach into the cell without isolating, testing, and following the facility’s safety program. OSHA’s arc-flash guide connects equipment condition and protective-device operation to the real hazard assessment. Maintenance access must be designed and managed separately from equipment classification.

A useful submittal comparison asks for the breaker positions, racking mechanism, mechanical and electrical interlocks, shutter arrangement, bus insulation, and compartment access. A photograph of a wheeled breaker cannot prove the complete assembly is built to C37.20.2. Ask for the manufacturer’s standard declaration and lineup drawings.

IEEE C37.20.3-2023 covers metal-enclosed interrupter assemblies above 1 kV through 48.3 kV. Its description includes interrupter switches, selector switches, power fuses, circuit breakers, instrumentation, metering, and protective equipment. Therefore a blanket sentence that “C37.20.3 only permits fused switches” is wrong. The standard names a category; the actual switching device comes from the product and project specification.

A common implementation is a load-interrupter switch with fuses for a transformer primary. Schneider Electric’s HVL/cc manual describes its metal-enclosed product under C37.20.3 and related standards, with interlocks for fuse and cable access. That is a specific product example, not a universal construction rule. The switch’s load-break capability, fuse fault-interruption duty, and any grounding-switch features need their own ratings.

Metal-enclosed equipment may also be arranged with fixed-mounted breakers. In that case, ask how the breaker is isolated and accessed, what must be de-energized for service, and which barriers separate adjacent energized parts. Do not infer “fixed” from C37.20.3 alone or “no interlocks” from the category. The OEM manual governs the actual sequence.

Eaton’s metal-enclosed application guide shows bus and switch ratings separately and describes options such as motor operators, blown-fuse indication, and relaying that need careful application. This is why the phrase “metal-enclosed, 15 kV” is still incomplete. It does not tell a reviewer whether the offered device interrupts load current, short-circuit current, or both, nor whether the required control and protection functions exist.

Compare the tested assembly and the offered device, not marketing headings. The table below is a decision checklist. It avoids claiming that every metal-enclosed product omits a particular feature; some OEMs add features beyond a standard’s minimum. For a 13.8 kV source feeding a transformer, a fused metal-enclosed switch may satisfy the chosen protection study. For a campus bus with multiple breakers, selective relays, and frequent feeder changes, a metal-clad assembly may better match the operating plan.

Use the standard edition on the submittal. IEEE C37.20.2’s 2025 abstract now covers metal-clad rated maximum voltages from 4.76 to 48.3 kV, while IEEE C37.20.3’s 2023 abstract includes devices beyond interrupter switches. IEEE’s metal-clad page and metal-enclosed interrupter page are more reliable for current scope than a decades-old catalog definition. The offered product may still have narrower ratings than the standard allows.

A mismatch can hide in a spreadsheet column. If the schedule says “breaker, drawout” but the general specification says “metal-enclosed,” bidders may interpret the latter as permission to offer a different construction. If the schedule says “fused load switch” but the prose demands “metal-clad,” the documents conflict the other way. Resolve the intended device and standard on the one-line before asking for substitutions.

A fused switch and a relay-operated breaker protect differently. A fuse has a manufacturer time-current characteristic and must be replaced after operating. A breaker is tripped by its protective relay and can normally be reset after the fault is investigated and corrected. Neither statement says which is safer for a particular feeder. A transformer with high inrush and a downstream low-voltage main needs a coordination study whichever primary device is chosen. Schneider Electric’s transformer-protection discussion gives a product-specific example of why fuse and relay application matters.

Maintenance can favor a drawout arrangement when the owner must remove a breaker without taking an entire lineup out of service. Yet that capability depends on the particular bus arrangement and safe work procedure. The feeder cable side may remain energized from another source, such as a generator or backfeed. The project should identify every source and the points used to isolate and test the circuit. OSHA’s guidance on verifying de-energization illustrates why an apparently open or disconnected device does not replace a task-specific hazard assessment.

Control and metering also differ by order. Ask whether the design requires remote trip and close, a specific relay, CT and VT ratios, event recording, status contacts, or SCADA communications. A product capable of housing a breaker does not necessarily include the controls you expected. The submittal must show the wiring and protective functions, not just the cubicle outline.

If a replacement lineup is being evaluated, map each existing feeder’s protection and operation into the candidate arrangement. A switchgear family with a matching voltage and BIL may have an incompatible cable approach, compartment access, control voltage, or bus layout. A construction label is useful only when paired with the actual one-line and room plan.

No. Metal-clad and metal-enclosed name assembly construction families. Arc-resistant performance is established through a separate internal-arcing-fault test designation under IEEE C37.20.7. IEEE’s C37.20.7-2024 correction sheet identifies the current recommended practice for switchgear up to 52 kV; Eaton’s arc-resistant guide lists tested accessibility types for one product. A buyer should request the actual tested designation, fault current, duration, and installation conditions.

A metal-clad lineup can be conventional rather than arc-resistant. A metal-enclosed load-switch lineup can be offered with arc-resistant construction. The enclosure category therefore cannot answer the question “where may an operator stand during an internal arc?” The arc-resistant switchgear guide explains Type 1, Type 2, B, C, and D and the exhaust path.

Likewise, an arc-resistant label does not make exposed energized work routine. OSHA’s arc-flash publication explains that incident energy, work task, equipment condition, and protective-device clearing time affect hazard assessment. The gear’s tested containment is one engineering control, applied only within its stated configuration. It does not replace isolation, maintenance, or PPE decisions for a task.

State the nominal system voltage, maximum equipment class and BIL, construction standard and edition, bus and device continuous current, calculated fault duty, one-line topology, and protection schedule. Then describe why the construction was chosen. “Metal-clad per IEEE C37.20.2, drawout breaker feeders” communicates a different design than “metal-enclosed interrupter switchgear per IEEE C37.20.3, fused transformer primary.” Both requests still need a device schedule and fault-study basis.

Add the practical constraints: indoor or outdoor location, cable entry and termination, front and rear access, shipping split, bus transition, control power, and documentation. For existing gear, ask for assembly and device nameplates, drawings, tested ratings, maintenance records, and any OEM-approved modifications. A substitute that meets the voltage class but changes the maintenance sequence should be reviewed as a design change.

Pantheon’s electrical catalog can be used to start a quote request. Send the one-line, duty, and required construction standard so we can check whether the network can source a matching assembly. The project engineer should review any proposed configuration against the required protection and maintenance behavior.

Describing C37.20.3 as only a fused switch. The current IEEE scope includes circuit breakers and other equipment. Identify the actual device in the offered assembly.

Assuming metal-clad means arc-resistant. The internal-arc test and installation conditions need a separate designation. A metal-clad label alone does not answer the arc question.

Assuming a drawout breaker makes every compartment safe to access. Other bus or cable compartments can remain energized. The operating instructions and isolation procedure govern work on the equipment.

Comparing only the two kV labels. A valid replacement must also meet BIL, current, short-circuit, protection, cable, control, and room constraints. The voltage-class guide explains that rating layer.