Quick Answer: Metal-Clad or Metal-Enclosed?
Choose metal-clad switchgear when safety during maintenance is paramount: critical substations, utility-owned equipment, and any installation where operators routinely access individual compartments while adjacent sections remain energized. Choose metal-enclosed switchgear when space and budget are constrained: commercial buildings, data centers, and installations where the equipment is accessed infrequently. Below we compare both types across construction, safety, cost, and real-world application.
Definitions: What the Standards Actually Say
The terms "metal-clad" and "metal-enclosed" have precise definitions in international standards. Understanding these definitions is critical because using the wrong type for a given application can result in code violations, safety hazards, and costly rework.
Metal-Enclosed Switchgear (IEC 62271-200 / GB 3906): Any switchgear assembly enclosed by a grounded metal housing. This is the broad, umbrella category. The enclosure provides basic protection against accidental contact with live parts and external environmental factors. However, the standard does not mandate internal barriers between every functional section.
Metal-Clad Switchgear (IEEE C37.20.2): A specific subset of metal-enclosed switchgear that requires grounded metal barriers between every major compartment — the main bus compartment, the circuit breaker compartment, the cable termination compartment, and the control/instrument compartment. Each compartment can be opened independently without exposing any live part in an adjacent compartment. The primary switching device must be removable (draw-out or withdrawable type).
In short: all metal-clad switchgear is metal-enclosed, but not all metal-enclosed switchgear is metal-clad. The distinction matters because specifications and local electrical codes often call for one or the other.
Construction Differences
Compartmentalization
Metal-clad switchgear divides the interior into four or more physically separate compartments using grounded sheet-metal partitions. The breaker compartment is fully isolated from the bus compartment, which is fully isolated from the cable compartment. Automatic shutters seal the bus and cable openings when the circuit breaker is withdrawn, preventing accidental contact.
Metal-enclosed switchgear may use internal partitions, but they are not mandatory between every section. Many designs use a single large enclosure with partial barriers or functional separations that do not provide the same level of arc containment.
Circuit Breaker Mounting
Metal-clad switchgear requires a draw-out (withdrawable) circuit breaker. The breaker rolls out on rails or a truck mechanism, and automatic shutters close over the bus and cable stabs when the breaker is removed. This allows the breaker to be inspected, tested, or replaced without de-energizing adjacent circuits.
Metal-enclosed switchgear may use either draw-out or fixed-mount circuit breakers. Fixed-mount designs are simpler, lighter, and less expensive, but they require the entire panel to be de-energized for breaker maintenance.
Internal Arc Performance
Because of full compartmentalization, metal-clad switchgear inherently provides better arc containment. If an internal arc fault occurs in the breaker compartment, the grounded barriers prevent the arc from propagating into the bus or cable compartments. Many metal-clad designs are tested and rated for internal arc classification (IAC) per IEC 62271-200 Annex A.
NAIJI Electric's ASN3-12 switchgear is rated for internal arc withstand of 50 kA / 1s, providing industry-leading arc safety for 12 kV applications.
Side-by-Side Comparison
| Parameter | Metal-Clad | Metal-Enclosed |
|---|---|---|
| Internal Barriers | Grounded metal barriers between ALL compartments | May or may not have internal barriers |
| Circuit Breaker | Draw-out (withdrawable) required | Draw-out or fixed-mount |
| Shutters | Automatic shutters on bus/cable stabs | Not required |
| Arc Containment | Arc confined to single compartment | Arc may propagate between sections |
| Maintenance Safety | Can open one compartment while others remain live | Often requires full de-energization |
| Size | Larger (more partitions, truck mechanism) | More compact (e.g. ASN550 at 550 mm depth) |
| Cost | Higher (30-50% premium) | Lower |
| Standards | IEEE C37.20.2 / IEC 62271-200 | IEEE C37.20.3 / IEC 62271-200 |
| Typical Voltage | 4.16 kV - 38 kV | 4.16 kV - 38 kV |
| Best For | Utility substations, critical facilities | Commercial buildings, data centers, light industry |
When to Choose Each Type
Choose Metal-Clad When:
- The specification or local code explicitly requires metal-clad construction
- Operators will perform live-adjacent maintenance (opening one compartment while others are energized)
- The installation is a utility substation, power plant, or critical facility where downtime must be minimized
- High fault levels (40-50 kA) demand superior arc containment
- The end user requires draw-out breakers for easy in-service replacement
Choose Metal-Enclosed When:
- Space is limited — compact panels like the ASN550 (550 mm depth) fit in tight electrical rooms
- The installation is a commercial building, bank, data center, or high-rise where access is infrequent
- Budget is a primary concern and full compartmentalization is not code-required
- Moderate fault levels (up to 31.5 kA) allow a simpler construction
- Fixed-mount breakers are acceptable for the application
NAIJI Electric Medium Voltage Switchgear Range
NAIJI Electric offers a complete lineup of metal-enclosed switchgear covering 12 kV to 40.5 kV:
- ASN3-12 — 12 kV, up to 5000 A / 50 kA, internal arc 50 kA/1s, AG3 vibration class, altitude up to 4,500 m
- ASN3i-12 — Intelligent version with IEC 61850 / MODBUS, real-time monitoring and remote diagnostics
- ASN550 — Ultra-compact 550 mm depth for commercial environments, up to 1250 A / 31.5 kA
- ASN2-24 — 24 kV, up to 4000 A / 40 kA, internal arc 31.5 kA/0.5s
- ASN1-40.5(G) — 40.5 kV, up to 3150 A / 40 kA, one of the most compact in its class
For help selecting the right switchgear type for your project, contact the NAIJI Electric engineering team.