Metal-Clad vs Metal-Enclosed Switchgear

"Metal-clad" and "metal-enclosed" get used as if they were the same panel, and that is exactly where a switchgear purchase goes wrong. They are not the same construction, and the difference is not cosmetic - it changes how a panel behaves during maintenance, during a fault, and across a decades-long service life. XIAOPAI - Wenzhou Xiaopai Electric Power Technology Co., Ltd. - manufactures both 12-40.5 kV metal-clad and metal-enclosed switchgear in Wenzhou, Zhejiang, so the distinction is a daily engineering decision on our production floor. This guide sets the two constructions side by side, pins down the rating and the breaker that sit behind each one, and shows what actually decides the choice.

1. WHAT THE TWO TERMS MEAN

Under IEC 62271-200, the dividing line between the two labels is the partition. A metal-clad panel has separate earthed metal compartments for the busbar, the switching device, the cable connection and the low-voltage equipment, each sealed off from the next by a metal shutter. A metal-enclosed panel is a single metal enclosure that holds the same equipment with far fewer internal partitions. Both are "metal-enclosed" in the everyday sense; metal-clad is simply the stricter, more compartmented end of that family. Getting the label right matters because it drives the safety, the footprint and the level of maintenance isolation downstream, and it is the first thing an engineer should ask a supplier to clarify before any rating is discussed. The three-decade argument over which construction to pick is still the clearest short read on the split, set out at metal-clad or metal-enclosed MV switchgear.

2. THE PARTITION IS THE POINT

What you buy with metal-clad construction is isolation. Because the breaker sits in its own earthed compartment behind a shutter, a rack-out for inspection does not expose the live busbar, and a fault in one compartment does not travel freely into the next. The partitions and shutters are earthed metal, so a phase-to-phase or phase-to-earth fault is contained where it starts rather than propagating across the whole board. That containment is what keeps an operator safe when a door is open and what keeps the healthy feeders energised while one feeder is worked on. Metal-enclosed panels trade some of that isolation for a smaller footprint and a simpler build, which is why they suit compact switchgear and ring main unit duty where the whole board is de-energised for any invasive work. The standard cubicle arrangements - single busbar, main plus transfer bus, and ring configurations - are mapped out at standard cubicle configurations for MV metal-enclosed switchgear.

3. PIN DOWN THE RATING

With the construction settled, the rating follows. XIAOPAI builds both metal-clad and metal-enclosed panels from 12 kV to 40.5 kV to IEC 62271-200, so the rated voltage, rated normal current and short-time withstand current remain the decision points whichever cabinet you choose. The rated voltage fixes the insulation level the panel must survive; the rated normal current fixes the continuous load the busbar and cable connections must carry without overheating; the short-time withstand current fixes how long the panel holds a fault before the breaker clears it. Each of these is a separate number, and they must be specified together. Every XIAOPAI unit is short-circuit and insulation tested in the factory before it ships. Ask for the routine test report that names the exact construction and rating you are buying, not a generic certificate that could belong to any panel. The same discipline applies at the low-voltage end, where XIAOPAI builds IEC 61439 compliant LV distribution cabinets that sit alongside the medium-voltage boards in a plant or building. Keeping the LV and MV standards separate in the specification avoids a common error: a panel that is rated correctly for one level and simply assumed to be rated for the other.

4. THE BREAKER INSIDE

The heart of either panel is the vacuum circuit breaker. XIAOPAI integrates the VSG-12 for compact switchgear, the VF2-12 for modular cubicle layouts, and the ZN85-40.5 withdrawable breaker for 40.5 kV indoor substations, all built on copper-chrome contact material and embedded-pole technology. The copper-chrome contact material resists welding under high fault current, while the embedded-pole construction seals the vacuum interrupter inside an epoxy pole, protecting it from dust, moisture and mechanical shock. The vacuum interrupter extinguishes the arc inside the sealed bottle at the first current zero, which is what lets a panel stay low-maintenance across a long service life without oil or gas handling. The breakers deliver a mechanical life above 10,000 operations and an electrical life up to 30 full short-circuit interruptions. Where the job is load switching rather than fault interruption, the FZRN12/25-12D vacuum load break switch with fuse combination handles 12 kV, 20 kA duty inside ring main units and compact substations, in a compact 96 x 58 x 93 cm footprint. The full model range is on the vacuum circuit breaker 12-40.5 kV page.

5. THE TESTS THAT PROVE IT

A nameplate is earned in the test bay, not in the brochure. XIAOPAI runs short-circuit and insulation tests on every panel before delivery, covering the IEC 62271-200 sequence of dielectric, temperature rise, short-time and peak withstand, mechanical function and degree of protection. The dielectric test proves the insulation survives the rated voltage plus a margin; the temperature-rise test proves the busbar and connections run within their thermal class at rated current; the short-time and peak withstand tests prove the panel holds a fault until the breaker clears it. These are not optional extras; they are the evidence that a metal-clad or metal-enclosed panel actually performs to the numbers on its plate. A certificate that does not name the exact construction, rating and breaker model you are buying is not worth the paper it is printed on. For ring main unit and compact substation duty, the FZRN12/25-12D load break switch page sets out how a single device combines load switching with current-limiting fuse protection.

6. WHERE EACH CONSTRUCTION FITS

The two constructions drift toward different sites. Metal-clad panels carry the substation feeders, power plant and mining switchboards where an operator must be able to rack out a breaker without approaching live parts, and where a fault must stay inside its own compartment so the rest of the board keeps running. Metal-enclosed panels carry the ring main units, compact substations and distribution rooms where footprint and feeder simplicity decide, and the enclosure itself is the protection. XIAOPAI supplies both, factory-assembled, short-circuit and insulation tested, with matching busbar, cable entry, earthing and SCADA interface options, plus export packaging, sea-freight crating and full engineering documentation for overseas installation. Typical installations span power utility secondary distribution, industrial plant main substations, commercial building distribution rooms, data centres and renewable energy step-up stations - the same sites where the metal-clad versus metal-enclosed question is decided by whether a breaker must be racked out against a live busbar.

7. HOW TO DECIDE

The choice reduces to a single question: how much is maintenance isolation worth against how much footprint it demands. Choose metal-clad when isolation and fault containment are non-negotiable - substation feeders, power plant and mining duty, or anywhere a rack-out must not expose the busbar. Choose metal-enclosed when footprint and simplicity decide - compact switchgear, ring main units and distribution rooms where the enclosure itself is the protection. Name the construction and the rating in the enquiry, and ask for the routine test report that matches them. That single habit filters out most of the wrong panels before the order is ever placed.