Introduction: Prysmian’s Flagship — The Premium NSHTÖU

PRYSMIAN Cordaflex® SMRT (N)SHTOEU is Prysmian Group’s premium-tier low-voltage reeling cable — the product that sits at the absolute top of the NSHTÖU performance hierarchy. With a 25 N/mm² maximum conductor tensile (the highest of any LV reeling cable in the entire Klaus Faber / Prysmian catalogue), an EPR inner sheath (unique among all the cables in this guide series), a consistently engineered 1.25× dynamic-to-permanent tensile ratio, and 31 total configurations including a massive 3×300+3×150/3 at 620 A / 22,500 N dynamic — the Cordaflex SMRT represents the engineering pinnacle of what is achievable in a VDE 0250-814 rubber reeling cable.

The “SMRT” designation indicates Prysmian’s enhanced-performance product tier — positioned above the standard CORDAFLEX (equivalent to TROMMELFLEX (K)) and above the KSM-S (which achieves 20 N/mm² with Gummi 5GM3 inner sheath). The Cordaflex SMRT combines every premium material choice available: rubber 3GI3 insulation, EPR inner sheath (replacing the standard Gummi 5GM3), rubber 5GM5 outer sheath, and the highest conductor tensile specification. For the most demanding crane applications — where cable failure consequences are measured in millions of euros of downtime — the Cordaflex SMRT is the specification that eliminates all compromise.

Technical Anatomy: Full Specification

Pure-Power Configurations: 9 Sizes from 3×35 to 3×300

Fiber Optic Configurations: 22 Variants with E9/G50/G62.5

The CORDAFLEX SMRT (N)SHTOEU (FO) provides 22 fiber optic configurations spanning 8 power cross-sections (3×35 to 3×300) with three fiber types (E9/125 singlemode, G50/125 multimode, G62.5/125 multimode) at 12 fibers per cable. The FO variants use dual-split protective earth (2×G/2) — one interstice occupied by the fiber tube, two by earth sub-conductors — matching the Trommelflex KSM-S FO architecture. All FO variants share identical Fzp, Fzd, and ampacity ratings as the equivalent power-only configurations, confirming that the fiber integration does not derate the cable’s mechanical or electrical performance.

25 N/mm²: The Highest Conductor Tensile of Any LV Reeling Cable

The Cordaflex SMRT achieves a maximum tensile strength at the conductor of 25 N/mm² — 25% higher than the KSM-S (20 N/mm²) and 67% higher than the standard TROMMELFLEX (K) (15 N/mm²). This is the absolute highest conductor tensile specification of any low-voltage reeling cable across all product families in the Klaus Faber and Feichun catalogues.

The 25 N/mm² limit means the Cordaflex SMRT can withstand higher pulling forces per unit of copper cross-section before conductor yield occurs. For the flagship 3×300+3×150/3 configuration (total copper: 300×3 + 150 = 1,050 mm²), the calculated Fzp at 25 N/mm² would be 26,250 N — but the datasheet lists 18,000 N, indicating the Kevlar-less central filler limits the cable’s practical tensile below the copper’s theoretical yield point. The 1.25× dynamic ratio then produces Fzd = 22,500 N. This 25 N/mm² specification reflects Prysmian’s premium conductor stranding technology — tighter lay lengths, optimised strand packing, and potentially higher-grade copper that achieves greater yield strength without sacrificing Class 5 flexibility.

Fzd/Fzp = 1.25×: The Engineered Dynamic Ratio

The Cordaflex SMRT is the only cable in this entire guide series that provides both Fzp (permanent tensile) and Fzd (dynamic tensile) across every configuration. The ratio is consistently Fzd = 1.25 × Fzp — meaning the cable can absorb 25% more force during dynamic shock events (hoist braking, acceleration, snagging) than it can sustain continuously under static suspension. This quantified ratio gives engineers a precise design tool for dynamic load analysis: once the static cable load is calculated (from cable weight, suspension length, and operational tension), multiply by 1.25 to determine the peak dynamic load the cable will experience during worst-case transient events.

For comparison: the Trommelflex KSM-S lists only Fzp — engineers must estimate the dynamic margin using rules of thumb (typically assumed 1.2–1.5×). The URSUS VS lists only Fzd — engineers cannot determine the permanent load limit from the datasheet alone. The Cordaflex SMRT eliminates both ambiguities by providing both values with a clear 1.25× relationship, enabling precise engineering without guesswork.

EPR Inner Sheath: Why It Matters More Than You Think

The Cordaflex SMRT uses an EPR (Ethylene Propylene Rubber) inner sheath — the only cable in this entire guide series to use EPR for the inner sheath rather than standard Gummi 5GM3. EPR is the same base polymer family as the 3GI3 insulation compound — creating a chemically compatible interface between the insulation and the inner sheath that prevents the chemical migration and delamination that can occur when dissimilar rubber compounds are in permanent contact under heat and pressure.

This material compatibility is critical in high-power cables carrying hundreds of amperes. At 620 A through 300 mm² conductors, the cable’s internal temperature gradient creates differential thermal expansion between adjacent material layers. If the inner sheath and insulation have different expansion coefficients (as occurs when 5GM3 neoprene is paired with 3GI3 EPR), micro-delamination can develop at the boundary over millions of thermal cycles — creating air voids that increase thermal resistance and accelerate insulation aging. The EPR inner sheath eliminates this failure mode by matching the insulation’s thermal and chemical characteristics, extending the cable’s dielectric life in the highest-current configurations.

Dual-Speed Rating: 160 Center-Feed / 200 End-Feed

The Cordaflex SMRT is the only cable in this guide series with a dual-speed rating: 160 m/min for center-feed drum applications and 200 m/min for end-feed applications. This distinction reflects the fundamentally different mechanical loads in the two reeling configurations. In center-feed operation, the cable crosses over the drum midpoint during each layer change — creating a transient bending reversal and fleet-angle stress that limits safe speed. In end-feed operation, the cable enters the drum from one end only — eliminating the crossover stress and allowing higher reeling speed. The Cordaflex SMRT’s construction can handle both duty profiles with specific speed limits optimised for each.

Cordaflex SMRT vs. Trommelflex KSM-S: The Premium Comparison

Choose Cordaflex SMRT when: the application demands the absolute highest mechanical performance (25 N/mm²), the 3×300 configuration at 620 A, published dynamic tensile data for precise engineering, or quad environmental certification (especially ozone resistance). Choose KSM-S when: the application requires −40°C dynamic operation (arctic terminals) or 4 kV dielectric test voltage for enhanced VFD transient protection.

Cost-Effective Alternative from Feichun

Feichun Lead Times: 8–12 weeks. European (Klaus Faber/Prysmian): 20–30 weeks.

Technical FAQ

Why does the SMRT achieve 25 N/mm² while the KSM-S achieves only 20 N/mm²?

The 25 N/mm² rating reflects Prysmian’s premium conductor stranding — optimised strand geometry and tighter lay lengths that distribute tensile stress more uniformly across the conductor’s individual wire strands. The EPR inner sheath may also contribute by providing better mechanical coupling between the conductor assembly and the sheath system, transferring tensile load more efficiently to the polyester braid torsion protection. The standard 5GM3 inner sheath in the KSM-S provides slightly less mechanical coupling, limiting the effective conductor tensile to 20 N/mm².

Why −35°C moving instead of −40°C like the KSM-S?

The EPR inner sheath has slightly different low-temperature flexibility characteristics compared to the Gummi 5GM3 used in the KSM-S. EPR maintains excellent properties well below −35°C, but the specific formulation used in the Cordaflex SMRT is optimised for thermal compatibility (matching the 3GI3 insulation) rather than extreme cold flexibility. For arctic terminals requiring −40°C dynamic operation, specify the KSM-S instead.

Can I mix Cordaflex SMRT power and KSM-S FO cables on the same reel?

This is not recommended. The two cable families have different outer diameters at equivalent cross-sections (e.g., 3×95: SMRT = 46.3 mm, KSM-S = 46 mm), different tensile characteristics (SMRT has 1.25× dynamic ratio), and different inner sheath materials that age at different rates. For the most reliable and maintainable cable system, standardise on one family for the entire reel system.