1. How many types of control cabinets are there? Classifying by core component is the most practical approach
By core component inside the cabinet, control cabinets fall into 4 categories:
| Type | Core components | Typical controlled equipment | Corresponding Photo from Zhejiang Golden Unicorn |
|---|---|---|---|
| PLC control cabinets | PLC + HMI + relays | Automated production lines / assembly lines | plc-control-box |
| VFD panels | VFD + braking unit | Pumps / fans / conveyors | cs-vfd-control-cabinet |
| Soft starter cabinets | Soft starter + bypass contactor | Reduced-voltage starting for large motors | auto-transformer-starter-cabinet |
| MCC control cabinet | Drawers + contactors + thermal overload relays | centralized multi-motor control | cs-double-door-control-cabinet |
Choose VFD for speed control, soft starter for starting without speed control, MCC for multiple centralized circuits, and PLC for complex logic. PLC cabinets are often used incombination with VFD or soft starter cabinets, not a replacement for it.
II. PLC Control Cabinets: The Workhorse of Factory Automation PLC + HMI + I/O expansion
The PLC control cabinet isthe most common cabinet type on factory automation lines. Its core components are:
- PLC main module: Siemens S7-200 SMART / S7-1200 / S7-1500, Mitsubishi FX5U, Omron CP1E, or domestic Inovance / Xinje
- HMI touchscreen: 7 / 10.1 / 15 in., MCGS / Weinview / Siemens KTP
- Digital / analog I/O modules: expanded as needed; commonly 16DI/16DO, 4AI/4AO
- 24V DC power supply: Mean Well / Siemens SITOP
- Relay bank: Schneider / Omron, one per circuit, interfacing PLC outputs with field loads
Standard dimensions of a Golden Unicorn PLC cabinet:800 × 600 × 2000 mm(W × D × H). A single cabinet can hold 1 PLC + 1 HMI + 64 points of I/O + 8 relay circuits + 1 24V power supply.
III. VFD Panels: VFD + PLC Working Together Speed control · Energy savings · Soft start in one
The core of a VFD panel is the VFD (variable frequency drive), which controls motor speed by changing the supply frequency. Typical applications:
| Applications | Typical power | Energy savings | Typical control signal |
|---|---|---|---|
| Pump constant pressure water supply | 5.5–75 kW | 20–50% | 4–20 mA pressure feedback |
| Fan speed control | 7.5–160 kW | 30–60% | PID temperature/pressure feedback |
| Conveyor speed control | 0.75–22 kW | 10–30% | 0–10 V speed reference |
| Compressor | 11–75 kW | 15–35% | Pressure feedback |
Golden Unicorn VFD panels use by defaultSchneider ATV320/ATV630 / ABB ACS580 / Siemens G120(customer's choice). Typical internal configuration: VFD + circuit breaker + contactor (bypass) + reactor (optional) + PLC communication interface (optional) + HMI.
IV. Soft Starter Cabinets: A Gentle Start for Large Motors Reduced-voltage starting · Protecting the grid
Soft starter cabinets solve the problem of "Large motors draw high inrush current on direct-on-line starting, which disturbs the grid.The core of the problem isSoft starter(thyristor voltage regulation):
- Startup phase: The thyristor firing angle ramps from 0 to full conduction, and voltage rises gradually from 30% to 100%.
- Run phase: The bypass contactor closes, the soft starter drops out, reducing its own heat generation.
- Stop phase: Optional soft stop, with voltage ramping down slowly from 100% to 0 to prevent water hammer.
Soft starter vs. VFD vs. star-delta — comparison of three options:
| Type | Speed control | Cost | Application |
|---|---|---|---|
| Soft starter | No | Medium | Reduced-voltage starting for large motors, 11–200 kW |
| VFD | Yes | High | Loads that require speed control |
| Star-delta | No | Low | Low-power motors, ≤ 22 kW |
11–75 kW motorsA soft starter is the most economical choice; if speed control is needed, use a VFD; for ≤ 22 kW with no speed control requirement, use star-delta to cut cost.Zhejiang Golden Unicorn: MOQ 1 unit, 15–25 days.
5. MCC motor control center: multi-drawer construction Multiple motors · Centralized · Easy to service
MCC (Motor Control Center) iscentralized multi-motor controlcabinet lineup, made up of multiple drawer units plus a common busbar. The construction is similar to a low-voltage drawer cabinet (GCS / MNS), but each drawer manages only 1 motor.
Single drawertypical configuration:
- Circuit breaker (QF): motor short-circuit protection
- Contactor (KM): motor start/stop control
- Thermal overload relay (FR): motor overload protection
- Current transformer (TA): signal acquisition
- Secondary terminals (X): field signal in/out
Zhejiang Golden Unicorn MCC cabinets support up to 9 drawer tiers / 9 motors Centralized control, suited to large workshops such as water treatment plants, chemical plants and power plants.
6. Shop-floor photos: 4 details of control cabinet assembly (workshop photos)
The following arephotographed on the assembly line at the Fengchuan Industrial Area workshop in TongluShot on site. GU ELECTRIC does not publish AI-rendered cut-out product images — we use real production-line photos only. If you need cut-out images for a catalog or brochure, message us on WhatsApp: +86 186 5712 0011.
FAQ FAQ
Can a PLC control cabinet and a VFD panel be installed together?
Yes, but there are rules to follow.VFDs generate harmonics that interfere with PLC communication. When the two share an enclosure, run the VFD poweron its own separate route, use shielded twisted-pair cable for signal lines, keep a distance of ≥ 200 mm, or separate them with a physical barrier. Our combined PLC + VFD panels have shipped to several water treatment and food line customers, with signal isolators fitted as standard.
Should a control cabinet body be carbon steel or stainless steel?
For indoor use, powder-coated carbon steel (60–80 μm thickness), which offers the best value; for coastal, chemical, food or outdoor use, specify 304 stainless steel.304 stainless steel adds about 30%, and 316 stainless steel adds about 60%. We supply powder-coated carbon steel as standard and can switch to 304 on request.
Does a control cabinet need EMC testing?
CE certification requires EMC testing(EN 61000-6-2 / 6-4). Our control cabinets are CE (LVD + EMC) certified as standard, with original documents available for review. Domestic 3C low-voltage assemblies do not mandate EMC, but project owners often require it in tenders.
How much price difference is there between a soft starter cabinet and a VFD panel?
At the same power rating,a soft starter cabinet costs 40–60% less than a VFD panel. The reason: a soft starter only performs reduced-voltage starting, while a VFD runs continuous speed control, so both the power devices and the cooling cost more.Which one to choose depends on whether you need speed control: use a VFD if you need speed control, use a soft starter if you only need reduced-voltage starting. Exact pricing is calculated by power rating and configuration — send us your drawings and we will quote.
What is the difference between an MCC cabinet and a GCS drawer cabinet?
An MCC is dedicated to motors, with each drawer controlling one motor(breaker + contactor + thermal overload relay + current transformer); a GCS drawer cabinet is more general-purpose and can serve different functions such as feeder, power factor correction or metering. Structurally, both GCS and MNS can be built as MCC solutions, but an MCC cabinet requiresmechanical interlockinginside each drawer (between the drawer and the main circuit).
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