Metal-enclosed and metal-clad switchgear are two different types of switchgear. More precisely, metal cladding is a specific subset of enclosing metals, just as squares are a specific subset of rectangles. These two types of electrical switchgear can sometimes be difficult to distinguish because they are so similar.
Available fault currents, safety considerations, and the impact of maintenance on the system are unique. These are the details you need to know in order to decide which style is right for your particular scenario.
1. What is metal armored switchgear?
ANSI C37.20.2-1987 defines metal-clad switchgear as metal-enclosed switchgear having three essential characteristics:
- Self-aligning and self-coupling removable (withdrawable) switch and interrupt devices move between connected and disconnected positions
- Automatic shutters conceal major thorns or studs when removable parts are disassembled, tested, or removed.
- Every major bus conductor, including connections, is fully insulated.
To ensure that the switchgear you have meets all ANSI standards, always look for a reputable supplier of medium-voltage switchgear.
2. Benefits of metal-clad switchgear
- Customization: Customization is one of the most attractive features of metal-clad switchgear. Customization depends on the complexity of the system application.
- Maintenance requirements vary based on customer application requirements. Some apps require fewer device switches. Its primary function is to act as a disconnect device, always in the “on” position except for the year off.
- Metal-clad switchgear provides enhanced safety measures not required by conventional metal-enclosed switchgear. For example, metal-enclosed switchgear is fully compartmentalized, meaning that the low-voltage compartment can be accessed without access to any other active components in the switchgear. The main bus and the approaching bus are also separated. The unit contains ground barriers, mechanical switches, circuit breaker shutters, and a fully insulated bus that separates the operator from medium-voltage components.
Why choose metal armored switchgear?
- A grounded metal barrier surrounds all live parts.
- Automatically operated shutters.
- Insulate the bus.
- Long mechanical and electrical life.
- Reliable circuit coordination.
- Proven transformer switchgear functionality.
3. What is metal-enclosed switchgear?
In accordance with ANSI C37.20.3-1987, metal-enclosed switchgear includes protective relays, power fuses (current-limiting or non-limiting), bare busbars with connections, instrument transformers, control wiring, and accessories. Load interrupter switching assemblies are governed by ANSI C37.20.3, C37.20.4, and C37.22.
Traditionally, a component required for such equipment is a high-pressure air switch. While most of these standards include temperature rise limits, ratings, conditions of use, testing, and construction, they also include current ratings, for example, as rated instantaneous current and rated short-time current. Often, these values are derived from the main component switchgear standards.
Why choose metal-enclosed switchgear?
- 600-1200A constant current rating
- 25-50kA short-time rating, unfused
- Limited switching (150-1000 mechanical operations typical)
- Typical Fuse Protection
- Lower operating expenses ($25K-$30K/switch NEMA1)
- easy to maintain
- Fast shipping (subject to stock availability – contact a reputable custom switchgear manufacturer)
- Interrupter switches are commonly used for load switching with fuses for fault protection.
- Proven substation switchgear
4. Metal cladding definition
Metal-clad switchgear (IEEE C37.20.2) shares many external characteristics with metal-encased switchgear. It’s completely encased in metal on all sides, save for the smaller vents and viewing holes. Also, the entire case is grounded, but that’s where the similarities end.
Cladding differs from metal enclosures in that all internal components are individually encased or compartmentalized in metal. Like bus bars, these components can also be individually insulated and grounded.
In addition, compartments can be removed individually with minimal impact on the overall system. All of these modifications add to the cost of metal cladding when comparing metal cladding versus metal closure.
5. Metal closure definition
The term “metal-enclosed switchgear” is self-explanatory. This is a switchgear housed in a metal enclosure. All surfaces of the internal components are metal except for minor ventilation and viewing holes. Additionally, the case is grounded to increase overall system safety.
Metal closures are divided into three subcategories,
- metal covering
- Low Voltage Power Circuit Breakers (IEEE C37.20.1)
- Metal Case Interrupters (IEEE C37.20.3).
MEIs (Metal Enclosed Interrupters) are essentially a simplified version of metal-covered switchgear. There are little or no obstructions between the internal parts of the two metal-enclosed switchgear. When the panel is open, most components are in one place. This feature helps reduce costs compared to metal-coated solutions.
6. The difference between metal composite switchgear and metal-enclosed switchgear
The following points discussed are a comparison of metal-clad switchgear and metal-enclosed switchgear:
- Metal cladding is approved for 10,000 operations, but metal closures are usually rated for less than 1000 operations. (exceptions apply)
- Load break ratings are generally not provided for metal-enclosed products.
- Fusible gears with metal casings are protected by protective relays, and fusible gears with metal casings are protected by fuses.
- Metal-clad circuit breakers are used, while metal-enclosed circuit breakers are usually fixed switches, circuit breakers, or fixed-mounted Vacs. CB. Withdrawable CB is available.
- The metal cladding is what separates, while the metal enclosure is the switch or breaker in the box, there is no isolated cable/bus/breaker section.
- Generally, metal-clad buses are insulated, but metal-enclosed standard buses are not.
- Metal-enclosed standards are always powered by electricity, while metal-enclosed standards are manually driven.
- Metal-clad is a three-cycle high-speed switching device; metal-enclosed fuses have durations ranging from 10 milliseconds to 600 seconds.
You should consider the following four factors when choosing custom switchgear: the total connected load, selected coordination requirements, safety requirements, and possible maintenance requirements. Analyzing metal cladding vs metal closure, metal cladding may be the best solution for greater weight and enhanced safety; closed metal may be a better solution for weight reduction.