1. Structural Definitions
Symmetrical Cable Structure
A symmetrical cable is one in which all conductors (e.g., three-phase power lines) are arranged in a geometrically balanced pattern, typically with:
Equal spacing between conductors
Identical insulation, shielding, and sheathing across all cores
Consistent physical and electrical characteristics
Example: A 3-core cable with conductors arranged in an equilateral triangle, surrounded by a common overall shield.
Asymmetrical Cable Structure
An asymmetrical cable features an uneven internal layout, where:
Core dimensions or insulation vary
Shielding may be applied to some conductors but not others
Conductor spacing is irregular
Example: A 4-core cable with three thick power conductors and one thinner ground wire, each with independent shielding.
2. Electrical Performance Comparison
| Feature | Symmetrical Cable | Asymmetrical Cable |
|---|---|---|
| Conductor Parameters | Identical electrical resistance, capacitance, and inductance | Varying electrical parameters across cores |
| Signal Integrity | Excellent signal balance, minimal crosstalk and noise | Higher susceptibility to signal distortion and interference |
| EMI Shielding | Strong electromagnetic interference (EMI) suppression | Weak EMI resistance, more prone to noise |
| System Compatibility | Ideal for sensitive or high-performance equipment | Sufficient for basic power and control systems |
3. Typical Application Scenarios
Symmetrical Cable Applications
Due to their balanced electrical properties and robust EMI resistance, symmetrical cables are used in:
Variable Frequency Drives (VFDs)
Servo motor control systems
Precision measurement and automation
High-speed signal transmission
Asymmetrical Cable Applications
More cost-effective and suitable for general purposes, asymmetrical cables are often found in:
Power distribution and lighting
Basic industrial control panels
General-purpose wiring where EMI is not a concern
4. Illustrative Diagrams
Symmetrical Structure Example
Three-core equilateral triangle layout with common shielding:
○
/ \
○—○ (Cross-section of cores arranged symmetrically)
[ Shielded outer sheath ]
Asymmetrical Structure Example
Four-core cable with three thick conductors and one small ground, independently shielded:
○ ○
○
[○] (Ground wire with individual shield)
5. Summary and Selection Guide
| Criteria | Symmetrical Cable | Asymmetrical Cable |
|---|---|---|
| Performance Priority | High-performance, sensitive environments | General purpose, low EMI risk |
| Cost | Higher due to design complexity | Lower, cost-effective for basic applications |
| Application Examples | VFDs, motors, instrumentation systems | Lighting, power supply, basic control |
Conclusion:
Selecting the right cable structure depends on your application’s electrical performance requirements, environmental conditions, and cost constraints. For noise-sensitive, high-precision equipment, symmetrical cables are the optimal choice. For routine power distribution or control wiring, asymmetrical cables offer a cost-effective solution.