How to Select Low-Voltage Switchgear? What Are the Differences Between the Four Major Types: GGD, GCS, GCK, and MNS?

Switchgear is a complete power distribution unit assembled by integrating primary and secondary equipment according to specific electrical wiring schemes. It primarily controls, protects, monitors, and distributes electrical energy to power lines and electrical equipment. Based on structural form, switchgear can be categorized into fixed-type and draw-out-type; by voltage level, it includes high-voltage switchgear (both fixed and draw-out types) and low-voltage switchgear (commonly fixed or drawer-type).

The overall structure of switchgear is generally similar, typically divided into several functional compartments. These primarily include: busbar compartments, circuit breaker compartments, secondary control compartments (also known as instrument compartments), and feeder compartments. Each functional compartment is usually isolated using steel plates to ensure operational safety and electromagnetic compatibility.

So, how should one correctly select low-voltage switchgear in practical applications? What are the differences between the four common types—GGD, GCS, GCK, and MNS? This article will provide a detailed analysis of each.

01

Structural and Performance Comparison of GGD, GCK, GCS, and MNS Low-Voltage Switchgear:

GGD is a fixed cabinet, while GCK, GCS, and MNS are drawer cabinets.

Both GCK and MNS cabinet frames use C-shaped profiles with a standard module E=25mm;

GCS cabinet frames use KS-shaped profiles with a standard module E=20mm.

The drawer-injection mechanisms differ between GCK cabinets and GCS/MNS cabinets;

GCS cabinets are limited to single-sided operation with cabinet depths of 400/600/800/1000/1200mm. The original GCS design supports a maximum current rating of only 4000A;

GCK cabinets have depths of 800/1000mm and can achieve a maximum rated current of 6300A;

MNS cabinets can be configured as double-sided operation cabinets with depths of 600/800/1000mm, capable of 6300A.

1. Fixed Cabinets

GGD is a fixed cabinet. Fixed cabinets do not specify modular dimensions (only drawer cabinets or fixed partition cabinets use modular dimensions, which will be discussed later). GGD AC low-voltage switchgear offers advantages such as rational structure, convenient installation and maintenance, excellent protection performance, and high breaking capacity. Its disadvantages include fewer circuits, inability to freely combine units, large footprint, and lack of computer connectivity.

2. Drawer Cabinets

GCK, GCS, and MNS are all drawer cabinets. Understanding drawer cabinets requires grasping the concept of the modular pitch E. E has two values: 20mm and 25mm. Currently, drawer cabinet bodies are typically fabricated using two types of profiles: KS profiles (E=20mm) and C profiles (E=25mm).

Given a cabinet height of 2200mm, the effective height for drawers (i.e., drawer height) is 1800mm. Therefore, both GCK profiles can accommodate 9 drawers: 8E (E=20) = 160 and 8E (E=25) = 200, both less than the 1800mm effective height.

Using E=25 as an example...

8E/4 = 200/4 (meaning 4 drawers are arranged in a 200mm-high space, each 150mm wide)

8E/2 = 200/2 (meaning 2 drawers are arranged in a 200mm-high space, each 300mm wide)

8E = Drawer height 200mm, width 600mm

12E = Drawer height 300mm, width 600mm

16E = Drawer height 400mm, width 600mm

20E = Drawer height 500mm, width 600mm

24E = Drawer height 600mm, width 600mm

2.1 GCK Switchgear

GCK Cabinet Dimensions:

Width: 400/600/800/1000/1200mm

Depth: 800/1000mm

Height: 2200/2300mm

Note: When the main busbar rated current is 6300A, the main busbar system employs a double-layer busbar configuration with a cabinet height of 2300mm. All other cabinet heights are 2200mm.

When the main busbar rated current is 5000A or below, the GCK switchgear can accommodate functional units with an effective height of 72E (E=25mm), allowing for a maximum of 9 layers of 1-unit (8E) outgoing circuits. When the main busbar rated current is 6300A, the GCK switchgear can accommodate functional units with an effective height of 64E (E=25mm), allowing for a maximum of 8 layers of 1-unit outgoing circuits. Functional units within the same cabinet may be entirely drawer-mounted, fixed-mounted, or a combination of both.

Functional unit compartments use 6E or 8E as the minimum height module.

When using 6E as the minimum height module, 12 functional unit drawers can be installed within a 72E mounting height.

When using 8E as the minimum height module, 9 functional unit drawers can be installed within a 72E mounting height.

Drawer units feature nine standard circuit ratings: 8E/4, 6E/2, 8E/2, 6E, 8E, 12E, 16E, 20E, 24E.

Fixed partition units feature four standard circuit ratings: 6E, 8E, 16E, 24E.

Three types of drawer circuit push mechanisms are available: XJG8(H1) manual crank push mechanism, XSL manual pull push mechanism, XJG8(H2) manual crank push mechanism for dedicated electric operation.

2.2 MNS Switchgear

The MNS system frame adopts a C-shaped skeleton with a standard module E=25mm;

MNS cabinet dimensions (HxWxD): 2200mm x 400/600/800/1000/1200mm x 600/800/1000mm

Standard drawer assembly specifications: 8E/4, 8E/2, 4E, 6E, 8E, 12E, 16E, 20E, 24E.

Note: Four 8E/4 or two 8E/2 assemblies can be installed horizontally in a 600mm-wide compartment with an assembly height of 8E (200mm). However, individual assemblies of 4E, 6E, 8E, 12E, 16E, 20E, and 24E require a 600mm-wide compartment, with the assembly height matching the specified dimension for that assembly size.

2.3 GCS Switchgear

The GCS frame is assembled from KS profiles with E=20mm;

GCS cabinet external dimensions (H x W x D): 2200mm x 400/600/800/1000/1200mm x 800/1000mm

The modular height of drawer units is 160mm, available in five size series: 1/2 unit, 1 unit, 1.5 units, 2 units, and 3 units.

02

Low-Voltage Switchgear Selection and Internal Circuit Breaker Layout Configuration:

In practice, regardless of the cabinet type, conventional designs prioritize aesthetic appeal and ease of installation. It is impractical to completely fill a cabinet to capacity. When selecting fixed-partition plug-in switchgear for low-voltage applications, the following guidelines may serve as a reference:

• Circuit Breakers:  

- For ratings of 1000A and above, choose frame-type air circuit breakers.  

- For ratings of 800A and below, select molded-case circuit breakers.

• Low-Voltage Output Switchgear Cabinet:  

The standard height of a low-voltage distribution cabinet is typically 2.2 meters. The effective mounting height for circuit breakers is 1.8 meters. Height requirements for different circuit breaker ratings are as follows:

• Molded-case circuit breakers below 250A: 200mm, occupying 8E space (equivalent to one drawer);

• 400A and 630A molded-case circuit breakers: 400mm, occupying 16E (equivalent to two drawers);

• 800A molded-case circuit breakers: 600mm, occupying 24E (equivalent to three drawers);

• Installation quantities for molded case circuit breakers in low-voltage switchgear (reference):

• For 800A molded case circuit breakers: 3 units per cabinet;

• For 400A and 630A molded case circuit breakers: 4 units per cabinet;

• For 250A and below molded case circuit breakers: 9 units per cabinet.