Online Consultation The electrical layout of the control cabinet directly affects the stability, maintenance convenience, and safety of the equipment. During the processing, it is necessary to comprehensively consider electrical principles, space planning, electromagnetic compatibility, installation and maintenance, and other aspects. The following are the core considerations for electrical layout:
1、 Principles for selection and layout of electrical components
1. Component selection and matching
According to the load power, select circuit breakers, contactors, and other components that match the rated current and voltage to avoid overload heating (such as selecting circuit breakers for motor circuits at 1.2-1.5 times the rated current).
Consider working system: High life contactors (such as AC-3 working system contactors suitable for motor control) should be selected for equipment that frequently starts and stops.
Reserved redundancy: The main switch and busbar are designed for future capacity expansion of 20% to 30%, and the terminal block is reserved with 10% to 15% spare points.
2. Functional area division
Power area: Place incoming circuit breakers and surge protectors (SPDs) at a distance of ≥ 100mm from signal lines to avoid electromagnetic interference.
Control area: PLC, relays, frequency converters and other control components are centrally arranged according to the signal flow direction (input → processing → output) to reduce cable crossing.
Power zone: High current components such as contactors and thermal relays should be kept away from precision control modules, with a recommended interval of ≥ 50mm.
Grounding area: Set up a separate grounding copper bar, with a short and thick grounding path (grounding wire cross-sectional area ≥ 1/2 of the phase wire), ensuring that the grounding resistance is less than 4 Ω.
2、 Space layout and installation specifications
1. Component installation spacing
Vertical direction: The distance between upper and lower components is ≥ 30mm, which is convenient for heat dissipation and wiring; Heating elements (such as resistors and transformers) should be installed on the top or side of the cabinet, away from the bottom cable entry.
Horizontal direction: The distance between adjacent component edges should be ≥ 20mm, and a maintenance space of ≥ 100mm should be left around large components (such as frequency converters).
Distance from the cabinet: The distance between the component and the cabinet shell should be ≥ 25mm (to prevent short circuits caused by touching the shell), and the distance from the cabinet door operation panel should be ≥ 50mm (for easy operation).
2. Cable trunking and cable layout
Separation of strong and weak electricity: Power cables (AC 380V/220V) and signal cables (DC 24V, communication lines) are laid in separate slots with a spacing of ≥ 50mm; if separation is not possible, metal partitions are required for isolation.
Cable trunking direction: Lay vertically/horizontally along the edge of the cabinet, with a turning radius of ≥ 6 times the outer diameter of the cable to avoid excessive bending of the cable.
Cable fixing: The entrance is sealed and fixed with gland heads, and a binding point is set every 300mm inside the cabinet. When multiple cables are bundled, a 10% margin should be left.
3、 Electromagnetic compatibility (EMC) and anti-interference design
1. Interference source control
High current components: contactors, relay coils in parallel with RC absorption circuits or freewheeling diodes to suppress arc interference during on/off operations.
Inverter layout: far away from PLC and sensors, with filters installed at the input/output terminals, and the casing reliably grounded (separately connected to the grounding copper bar).
2. Protection of sensitive components
Signal cables: Analog and communication lines (such as RS485 and CAN bus) use twisted pair shielded wires, with the shielding layer grounded at one end (usually on the controller side).
Sensor power supply: DC power supply (such as 24V) should be supplied separately to avoid sharing power with the power circuit. If necessary, an isolation transformer should be added.
3. Optimization of grounding system
Classification grounding: protective grounding (PE), working grounding (NE), and shielding grounding should be set separately to avoid forming grounding loops.
Grounding path: Grounding wire cross-sectional area: Power circuit ≥ 4mm ², signal circuit ≥ 2.5mm ², connected to the grounding bar using a short straight path.
4、 Heat dissipation and protection design
1. Heat dissipation planning
Natural heat dissipation: Heating elements (such as switch power supplies and power modules) are installed on the top of the cabinet, utilizing the principle of thermal convection to dissipate heat; Ventilation holes are provided at the bottom and top of the cabinet (with dust-proof nets installed).
Forced cooling: When the power of the cabinet is ≥ 2kW, install an axial fan or air conditioner. The fan is installed at the bottom for air intake and at the top for air outlet, forming an airflow channel.
Thermal management: Apply thermal grease between power components and mounting plates to reduce contact thermal resistance.
2. Protection level
Environmental adaptation: Select the cabinet protection level according to the usage scenario (such as IP54 dust and water spray, IP65 strong water spray), and seal the cable entrance with a sealing rubber ring.
Insulation spacing: The electrical clearance between high-voltage components (such as ≥ 660V) is ≥ 10mm, and the creepage distance is ≥ 12.5mm (adjusted according to the pollution level).
5、 Identification and maintenance convenience
1. Clear identification
Component identification: Each component is labeled with a permanent identification plate (such as "QF1- Incoming Circuit Breaker"), and the terminal block is labeled with the wire number (consistent with the schematic).
Circuit identification: Install number tubes at both ends of the cable to indicate the circuit number (such as "L1-1 # motor control line").
2. Maintain space
Pre maintenance design: Components are centrally installed on the back panel of the cabinet door, and can be directly inspected after the cabinet door is opened (attention should be paid to the load-bearing capacity and hinge strength of the cabinet door).
Reserved testing points: Set up testing terminals in critical circuits (such as power supply, signal input and output) for easy troubleshooting.
6、 Compliance with safety regulations and standards
1. Electrical safety
Anti electric shock protection: Live parts (such as busbars) should be insulated and sheathed. The exposed terminals should be at least 25mm away from the edge of the cabinet, and there should be no exposed live parts after the cabinet door is closed.
Short circuit protection: Each branch circuit is equipped with a circuit breaker or fuse, and the upper and lower protection components need to be coordinated (such as the rated current of the upper circuit breaker being ≥ 1.4 times that of the lower circuit).
2. Industry standards
Adhere to standards such as GB 7251.1-2013 "Low Voltage Switchgear and Control Equipment" and IEC 61439-1 to ensure that the creepage distance, electrical clearance, and protection level meet the requirements.
When it comes to explosion-proof environments, explosion-proof components should be selected and meet the GB 3836 series explosion-proof standards.
Summary: Key Checkpoints
Standard requirements for inspection items
The distance between strong and weak electricity is ≥ 50mm (or metal isolation)
Grounding resistance ＜ 4 Ω
Component installation spacing: Vertical ≥ 30mm, horizontal ≥ 20mm
Cable trunking bending radius ≥ 6 times the outer diameter of the cable
Protection level meets the usage environment (such as IP54)
The clarity of the identification is consistent with the schematic diagram, with permanent identification
Through systematic layout design, strict installation processes, and adherence to standards, the reliability, safety, and maintainability of the electrical control cabinet can be ensured, reducing later debugging and operation costs.
