Metal Clad vs. Metal Enclosed Switchgear: Understanding the Differences
Metal clad and metal enclosed switchgear are two distinct categories of medium-voltage equipment. While both provide protective enclosures for electrical components, metal-clad switchgear represents a more specific, higher-performance subset of metal-enclosed switchgear—similar to how a square is a specific type of rectangle. Due to their similar appearance, it can be difficult to distinguish between the two, but key differences lie in their construction, functionality, safety features, and maintenance characteristics.
1. What Is Metal Clad Switchgear?
According to ANSI C37.20.2-1987, metal clad switchgear is a form of metal enclosed switchgear that includes the following key features:
- Removable Circuit Elements: Devices such as circuit breakers are withdrawable, moving between connected, test, and disconnected positions with self-aligning and self-coupling mechanisms.
- Automatic Safety Shutters: When components are removed or tested, shutters automatically cover live parts.
- Fully Insulated Bus: All major bus conductors and their connections are completely insulated.
To ensure full ANSI compliance, it is important to source this type of switchgear from a reputable medium-voltage manufacturer.
2. Advantages of Metal Clad Switchgear
- High Customization: Metal clad switchgear can be tailored to complex system requirements.
- Compartmentalization for Safety: Components such as the main bus, feeder bus, and control devices are physically separated by grounded metal barriers.
- Maintenance Flexibility: With drawout breakers and isolated compartments, maintenance can be performed safely and efficiently.
- Enhanced Protection: Circuit breaker shutters, ground barriers, and robust insulation protect operators from medium-voltage hazards.
- Durability and Reliability:
- Long mechanical and electrical life
- Coordinated protection for upstream and downstream systems
- Proven performance in transformer protection applications
3. What Is Metal-Enclosed Switchgear?
Defined under ANSI C37.20.3-1987, metal-enclosed switchgear typically includes:
- Protective relays, fuses (current-limiting or not), busbars, instrument transformers, and control wiring
- Interrupter switches for load switching
- Enclosures with grounded metal barriers and standard access points
Commonly used for indoor or outdoor power distribution, metal-enclosed switchgear offers reliable performance at a more economical price point.
4. Why Choose Metal-Enclosed Switchgear?
- Standard Current Ratings: 600–1200 A continuous
- Short-Time Ratings: 25–50 kA, typically unfused
- Moderate Switching Duty: Usually rated for 150–1000 mechanical operations
- Simplified Protection: Fuse-based fault interruption
- Cost-Effective: Lower upfront investment and faster availability
- Ease of Maintenance: Less complex systems reduce downtime and simplify servicing
5. What Does “Metal-Clad” Mean?
Metal-clad switchgear is fully enclosed in grounded metal on all sides except for ventilation or viewing openings. What sets it apart is that each internal component is housed in its own metal compartment, enhancing both safety and reliability. These isolated compartments can be individually removed without disrupting the rest of the system. The added safety and flexibility, however, come with increased cost and complexity.
6. What Does “Metal-Enclosed” Mean?
The term refers to switchgear contained within a grounded metal enclosure. Internally, however, the components are generally not isolated from one another. This design is less expensive and more compact but offers reduced fault containment and lower operational flexibility. Metal-enclosed switchgear includes:
- Metal-Enclosed Interrupters (MEI) – Simplified systems with shared internal spaces
- Low-Voltage Power Circuit Breakers – As defined in IEEE C37.20.1
- Standard Load Interrupters – Governed by ANSI/IEEE C37.20.3 and C37.22
7. Key Differences at a Glance
| Feature | Metal-Clad | Metal-Enclosed |
|---|---|---|
| Operations Rating | Up to 10,000 | Typically <1,000 |
| Busbar Insulation | Fully insulated | Usually bare |
| Breaker Type | Withdrawable circuit breaker | Fixed breaker or interrupter switch |
| Compartmentalization | Fully isolated components | Minimal or no separation |
| Safety Features | High – grounded barriers, shutters | Moderate |
| Maintenance Access | Easier and safer | Requires full shutdown in many cases |
| Protection Scheme | Relay-based | Fuse-based |
| Cost | Higher | Lower |
| Applications | Critical systems with high reliability | Standard commercial/industrial use |
8. Choosing the Right Switchgear
When selecting between metal-clad and metal-enclosed switchgear, consider the following:
- Load capacity
- Protection and coordination requirements
- Safety standards
- Maintenance frequency and system uptime needs
If your project demands high safety, frequent maintenance access, or advanced protection schemes, metal-clad switchgear is likely the better choice. For less demanding environments with budget constraints, metal-enclosed switchgear may offer sufficient performance at a lower cost.
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