1. Introduction to RHEYFIRM® (S) Series Cable Architecture

The RHEYFIRM® family represents Nexans’ flagship line of flexible medium-voltage reeling cables, engineered specifically for extreme mechanical stress applications including Ship-to-Shore (STS) cranes, Rail Mounted Gantry (RMG) cranes, stacker reclaimers, and heavy mobile mining equipment. The “(S)” designation indicates the symmetrical configuration featuring the distinctive 3+3 core design, where three phase conductors are complemented by three protective earth conductors strategically positioned in the cable interstices.

According to DIN VDE 0250 Part 813, the standard governing trailing and reeling cables for power installations, this six-core configuration offers superior electromagnetic characteristics compared to conventional single-earth designs. The distributed earth approach positions earth conductors symmetrically around the cable’s circumference, fundamentally altering the electromagnetic field distribution during operation.

2. Technical Rationale for Distributed Earth Design

2.1 Electromagnetic Field Cancellation Principle

The fundamental principle underlying the distributed earth design relates to electromagnetic field cancellation. In a three-phase power system, the vector sum of currents in the three phase conductors equals zero under balanced load conditions. By positioning three separate earth conductors in the interstices between phase cores, Nexans achieves a geometric configuration where return currents are distributed symmetrically, creating counter-electromagnetic fields that partially cancel the fields generated by the phase conductors.

2.2 Transfer Impedance Optimization

Transfer impedance represents a critical parameter in EMC cable performance, measuring the voltage developed on the shield per unit current flowing through the conductor per unit length. The Varolex® series from Nexans demonstrates how distributed earth design, combined with 100% coverage copper tape screening, achieves superior transfer impedance characteristics compared to traditional braided cable constructions. Lower transfer impedance directly correlates with reduced electromagnetic emissions and improved immunity to external interference.

3. EMC Performance Impact Analysis

3.1 Conducted Emissions Reduction

The distributed earth configuration significantly reduces conducted emissions by providing multiple low-impedance return paths for high-frequency currents. According to IEC 61000-6-4, the generic EMC emission standard for industrial environments, equipment must demonstrate compliance with conducted emission limits in the frequency range from 9 kHz to 400 GHz. The symmetrical earth arrangement ensures that fault currents and transient disturbances are distributed evenly, preventing the concentration of high-frequency energy that typically causes conducted EMI problems.

3.2 Radiated Emissions Mitigation

Cables function as transmission lines and potential antennas in industrial installations. The RHEYFIRM® (S) design addresses radiated emissions through the principle of field cancellation, where the distributed earth conductors create opposing magnetic fields that reduce the net electromagnetic radiation escaping from the cable assembly. This characteristic proves particularly valuable in port and crane applications where cables must coexist with sensitive control systems, communication equipment, and navigation aids without causing interference.

3.3 Common Mode Noise Suppression

Common mode interference represents one of the most challenging EMC issues in industrial cable installations. When forward and return current paths are separated by significant distances, the resulting loop acts as an antenna susceptible to electromagnetic coupling. The 3+3 distributed earth design minimizes the effective loop area by positioning earth conductors adjacent to their corresponding phase conductors, reducing common mode coupling by maintaining the return current path in close geometric proximity to the source current.

4. Technical Specifications Comparison

5. Application Considerations and Installation Guidelines

5.1 Proper Earthing Connections

To realize the full EMC benefits of the distributed earth design, all three earth conductors must be properly terminated and bonded at both cable ends. According to EMC best practices documented by Schneider Electric and LAPP, shield earthing should be performed over a large contact area using 360-degree bonding techniques. The parallel connection of three earth conductors effectively reduces the overall earth impedance to approximately one-third of a single conductor configuration, particularly beneficial at high frequencies where skin effect increases conductor impedance.

5.2 Cable Segregation Requirements

Despite the superior EMC characteristics of RHEYFIRM® (S) cables, proper segregation from sensitive circuits remains essential. According to industrial EMC guidelines, output cables from variable frequency drives (Class 4 interference sources) should maintain minimum separation distances from control cables (Class 2) of at least 450mm for cable runs of 30 meters, with separation requirements scaling for longer installations.

6. Compliance Standards Reference

7. Conclusion

The RHEYFIRM® (S) 3+3 core design represents a sophisticated engineering solution to the electromagnetic compatibility challenges inherent in high-power mobile equipment applications. By distributing three protective earth conductors symmetrically in the cable interstices, Nexans achieves electromagnetic field cancellation, reduced transfer impedance, and superior common mode noise rejection compared to conventional single-earth configurations. These characteristics make the (S) series particularly suitable for demanding industrial environments where EMC compliance, operational reliability, and signal integrity are paramount concerns.