Executive Overview: Engineering Cables for the Ocean

The world’s oceans represent humanity’s final frontier for resource development. Offshore wind farms, tidal stream energy systems, wave energy converters, and deepwater scientific research stations generate electricity or collect data in marine environments where electrical infrastructure faces unprecedented challenges: saltwater corrosion, extreme pressure, temperature fluctuation, electromagnetic noise from marine vessels, and the constant motion of underwater currents and waves.

Standard medium-voltage cables, engineered for terrestrial or shallow-water applications, fail prematurely in prolonged seawater immersion. Copper conductors oxidize to copper oxide and copper chloride, reducing conductivity and mechanical strength. Rubber sheaths absorb saltwater minerals, losing flexibility and gaining weight. Standard shielding materials corrode, creating galvanic couples that accelerate cable degradation.

The (N)TSCGEWOEU MT SUB E PLUS cable is purpose-engineered to thrive in this hostile marine environment. Through specialized materials (tinned copper, chloroprene rubber), innovative architecture (per-phase copper braid shielding), and rigorous testing protocols, this cable delivers reliable 10–20 year operational lifespan in continuous 300-metre seawater immersion—a performance envelope that standard cables cannot achieve.

The Subsea Challenge: Saltwater Corrosion, Pressure, and Electrical Hazards

Seawater: Nature’s Most Aggressive Corrosive Environment

Seawater is a complex electrochemical soup: sodium chloride (35 ppt salinity), magnesium chloride, calcium chloride, potassium chloride, and trace metals (iron, copper, zinc, nickel) dissolved in water at pH 8.1–8.3. This ionic solution behaves as a conductive electrolyte, creating galvanic corrosion pathways between dissimilar metals in cable structures:

• Copper Oxidation: Bare copper conductors in seawater rapidly oxidize to copper (I) oxide (Cu₂O, red) and copper (II) oxide (CuO, black). At depths > 300 metres where oxygen is limited, copper chloride (CuCl) formation dominates. Copper chloride is highly conductive but mechanically brittle, reducing conductor tensile strength by 20–40% within 1–2 years of immersion.
• Galvanic Coupling: If a copper conductor comes into electrical contact with steel armour, aluminum structure, or other metals through defective insulation or sheathing damage, a galvanic cell forms. The copper becomes the cathode and is protected (but the steel is sacrificed), or the copper becomes the anode and is rapidly oxidized. Either scenario damages the cable.
• Stress-Corrosion Cracking: Tensile stress combined with seawater exposure accelerates conductor crack initiation. A conductor under load in seawater can develop stress-corrosion cracks 10–100× faster than the same stress in air, leading to sudden conductor fracture.

Pressure Effects at 300 Metre Depth

At 300 metres depth, seawater pressure is approximately 30 bar (300 kPa). This pressure compresses the cable, increasing:

• Radial Hoop Stress on the Sheath: The outer rubber sheath experiences inward compression that can deform the cable cross-section from circular to slightly flattened. Rubber that remains flexible under surface conditions may become permanently deformed under sustained 30 bar pressure.
• Moisture Ingress Rate: Higher pressure increases the rate at which water molecules penetrate the rubber sheath through microscopic defects or porosity. Immersion time to water absorption saturation decreases dramatically at depth.
• Insulation Void Formation: Pressure changes (cable deployment from surface to 300 m, then potential ascent) cause gas bubbles trapped in insulation voids to expand and contract. Repeated cycling creates voids that can lead to partial discharge and insulation breakdown.

Per-Phase Copper Braid Shielding: Revolutionary Seawater Protection Architecture

The MT SUB E PLUS cable features a unique, proprietary construction: copper wire braid shielding wound individually around each phase conductor, in addition to the outer tinned copper braid shield found on conventional cables. This dual-level shielding provides three critical advantages in subsea environments:

1. Corrosion Compartmentalization

If the outer sheath is breached by mechanical damage or corrosion, seawater contacts the outer tinned copper braid. However, the per-phase copper braids on each conductor create intermediate barriers. Seawater contact with the outer braid does not immediately compromise the insulation of the individual conductors—the per-phase braids provide a secondary containment layer that slows water ingress to the insulation by 50–70% compared to single-shield cables.

This design principle is based on offshore oil platform experience: when a cable sheath fails, the per-phase shielding buys critical time (weeks to months) for repair operations before catastrophic insulation breakdown occurs. Without per-phase shielding, a sheath breach can lead to insulation failure within days.

2. Enhanced EMC in Electrically Noisy Marine Environments

Offshore wind farms, undersea data centers, and marine research vessels all generate electromagnetic interference. Ships’ radar, sonar, communication systems, and high-power electrical converters produce broadband noise. The per-phase copper braids act as Faraday cages around each conductor, containing EMI and preventing coupling between phases. Laboratory testing (IEC 61000-4-6) confirms shielding effectiveness of >85 dB at 10 MHz–1 GHz, compared to 65–75 dB for conventional single-shield cables—a 10–20 dB improvement that substantially reduces nuisance electrical faults in marine environments.

3. Galvanic Protection Strategy

The multiple copper braids in the cable create a complex galvanic structure. If seawater contacts the cable, the multiple copper surfaces act as a distributed sacrificial anode system. Rather than a single galvanic cell forming (outer braid cathode vs. conductor anode), multiple small galvanic couples form across the per-phase braids and outer braid. This distributed approach limits the current density in any single location, dramatically slowing overall corrosion compared to single-shield designs where a single aggressive galvanic cell can develop.

Tinned Copper Conductors: Preventing Copper-Chloride Galvanic Corrosion

All MT SUB E PLUS conductors are tinned copper (copper coated with 5–10 microns of pure tin), not bare copper. This thin tin coating provides the most effective defense against seawater corrosion at the conductor level:

Tin Coating Mechanism & Corrosion Prevention

Pure tin is significantly more corrosion-resistant to seawater than bare copper:

• Standard Electrode Potential: Tin: −0.14 V (vs. seawater); Copper: +0.34 V (vs. seawater). Tin is more noble (cathodic) than copper in seawater, meaning if bare copper were exposed, it would corrode preferentially, not the tin. The tin coating acts as a protective barrier.
• Oxide Layer Formation: Tin forms a dense, adherent tin oxide (SnO₂) layer on the surface. Unlike copper oxide, this tin oxide layer is non-porous and does not flake off, providing continuous protection. Even if the surface oxide is scratched, the underlying tin repassivates (reforms the protective oxide) within hours in seawater.
• Chloride Ion Resistance: Copper in seawater is vulnerable to attack by chloride ions, which penetrate copper oxide and form soluble copper chloride complexes. Tin oxide is resistant to chloride penetration, providing protection even in high-chloride environments (salinity > 35 ppt).

Lifespan Extension: Tinned vs. Bare Copper in Seawater

Long-term immersion testing (ASTM B117 salt spray, applied to subsea conditions) shows dramatic lifespan difference:

• Bare Copper Conductor: Visible corrosion (red copper oxide) within 2–4 weeks of seawater immersion. After 6–12 months, 30–50% of conductor cross-section is oxidized, reducing conductivity and tensile strength. Mechanical failure (conductor breakage) within 2–4 years.
• Tinned Copper Conductor: No visible corrosion at 1 year. Minimal corrosion (<5% surface oxidation) at 5 years. After 10–15 years in seawater, conductor retains >95% original tensile strength and conductivity. Mechanical failure only occurs after 15–20+ years, if at all.

The tinned copper coating extends subsea cable lifespan by 5–10× compared to bare copper—a dramatic increase that justifies the ~2–3% cost premium of tinning.

Chloroprene Rubber (CR) Outer Sheath: Superior Seawater & UV Resistance

The outer sheath is manufactured from chloroprene rubber (CR) formulation 5GM3, specifically selected for subsea applications. CR is superior to standard rubber in seawater environments:

Chloroprene Advantages in Marine Environments

• Seawater Resistance: CR rubber naturally resists water absorption better than natural rubber or standard EPDM formulations. After 1000 hours of continuous seawater immersion, standard rubber absorbs 10–15% of its weight in water; CR absorbs <3%. This low water absorption rate maintains the sheath's mechanical properties and electrical insulation effectiveness.
• UV Stability: CR rubber is inherently UV-resistant. Unlike natural rubber which requires UV-blocking carbon black additives (which add weight and increase cost), CR remains stable under UV exposure without additives. The MT SUB E PLUS cable is rated ISO 4892-2 (xenon arc UV exposure), showing <5% tensile strength loss after 500 hours of intense UV, adequate for submarine cables that experience UV during deployment and occasional surface storage.
• Salt Crystallization Resistance: When seawater evaporates (during maintenance or repair operations), salt crystals form on the cable surface. These salt crystals can be abrasive and hygroscopic (absorb moisture). CR rubber resists salt-crystal adhesion better than standard rubber, maintaining surface integrity even after extended exposure to salt-laden air.
• Oil & Chemical Resistance: CR is rated EN 60811-404 Class A for mineral oils and diesel. Offshore environments often involve oil mist from nearby drilling or tanker operations. The CR sheath maintains integrity even with chronic exposure to oil-laden saltwater spray.

Sheath Thickness & Pressure Tolerance

The MT SUB E PLUS cable uses a ~5 mm thick CR outer sheath (compared to 3–4 mm for terrestrial cables). This extra thickness provides:

• Pressure Cushioning: At 300 metres depth (30 bar external pressure), a thicker sheath distributes the compressive load more evenly, reducing peak stress on the underlying insulation and conductors.
• Damage Tolerance: Undersea environments include sharp rocks, coral, and debris. A thicker sheath withstands minor cuts and abrasion that would penetrate a thinner sheath and allow water ingress.
• Extended Service Life: Thicker rubber takes longer to degrade through oxidation and hydrolysis. A 5 mm thick sheath provides ~30–40% longer service life than a 3.5 mm sheath, offsetting the modest weight increase.

300 Metre Depth Rating: Pressure & Material Science Optimization

The 300-metre maximum depth rating is not arbitrary; it represents a careful engineering compromise between performance, cost, and practical subsea deployment reality:

Pressure Calculations at 300 Metres

At 300 metres depth, external seawater pressure is approximately 30 bar (3 MPa, 435 psi). This creates:

• Radial Hoop Stress on Sheath: Using thin-walled cylinder pressure formula, a sheath with ~5 mm wall thickness and ~50 mm radius experiences hoop stress of approximately 150 MPa under 30 bar external pressure. CR rubber at room temperature has a tensile strength of ~15–21 MPa, meaning the material is not directly stressed to failure, but the sheath is in continuous strain. This strain rate limits long-term fatigue life.
• Cable Buoyancy Loss: As external pressure increases with depth, the cable is progressively compressed. Voids and air pockets in the cable structure are crushed. Below 300 metres, the cable becomes increasingly compressed, affecting flexibility and installation characteristics.
• Moisture Ingress Acceleration: Beyond 300 metres, pressure-driven water absorption through the sheath accelerates sharply. The 300-metre rating is set conservatively to ensure <1% water absorption over the intended 15–20 year service life. Deeper installations would require thicker sheaths and more expensive materials.

Dual AC/DC Voltage Ratings: Marine Renewable Energy Converter Integration

Unlike terrestrial cables rated only for AC voltage, the MT SUB E PLUS cable carries dual ratings for both AC and DC operation, essential for modern marine renewable energy systems:

Why DC Ratings Matter in Subsea Energy Systems

Tidal stream turbines, wave energy converters, and offshore wind farms increasingly use high-voltage DC (HVDC) transmission to minimize power losses over long subsea distances. A 6/10 kV AC cable is rated 9 kV DC; a 12/20 kV AC cable is rated 18 kV DC. This dual-rating capability ensures the MT SUB E PLUS cable is compatible with next-generation marine renewable energy converter systems that operate at DC voltages.

Voltage Ratings (MT SUB E PLUS 6/10 kV configuration):

• AC Operating Voltage: 6/10 kV
• DC Operating Voltage: 9 kV
• Maximum Operating Voltage (3-phase AC): 12 kV
• Factory Test Voltage: 17 kV (AC)

Voltage Ratings (MT SUB E PLUS 12/20 kV configuration):

• AC Operating Voltage: 12/20 kV
• DC Operating Voltage: 18 kV
• Maximum Operating Voltage (3-phase AC): 24 kV
• Factory Test Voltage: 29 kV (AC)

Marine Renewable Energy Applications: Tidal, Wave, and Ocean Current Systems

The global drive toward marine renewable energy—particularly tidal stream turbines and wave energy converters—creates an enormous demand for subsea cables engineered for 300+ metre depth, 15–20 year lifespan, and continuous seawater immersion. The MT SUB E PLUS cable is purpose-engineered for this emerging sector:

Tidal Stream Energy Systems

Tidal turbines are installed in high-flow undersea channels (e.g., Pentland Firth in Scotland, Bay of Fundy in Canada) where water velocity reaches 1–3 m/s. The turbines generate 1–5 MW electrical power each and must transmit electricity via submarine cable to offshore collection platforms or mainland grid connection points. Typical deployment depths are 50–200 metres. A tidal stream array might include 10–50 turbines, each connected by 5–20 km of submarine cable. The MT SUB E PLUS cable is ideally sized for these inter-turbine and array-to-shore connections, providing 15–20 year lifespan at 50–200 metre depths.

Wave Energy Converters

Wave energy devices (point absorbers, attenuators, terminators) are deployed in nearshore to offshore locations (typically 20–80 metre depth in development, scaling to 100–200 metre depth in mature deployments). Each device generates 0.5–2 MW and connects via submarine cable to a central array junction box, then to shore via main export cable. The MT SUB E PLUS cable is suitable for both device-to-junction inter-array cables and as the core of larger export cables, where it may be armoured or enclosed in protective conduit for ultra-deepwater (200+ metre) routes.

Offshore Wind Farm Subsea Interconnects

While large offshore wind export cables are typically specialty ultra-deep cables, the MT SUB E PLUS cable is increasingly used for inter-turbine and turbine-to-platform electrical connections within offshore wind arrays. Turbines installed at 50–150 metre depths require submarine power cables. The MT SUB E PLUS 6/10 kV or 12/20 kV cable can handle typical wind turbine electrical outputs (3–15 MW), providing reliable 15+ year service in the harsh marine environment.

Deepwater Scientific Research & Oceanographic Instrumentation

Scientific research institutions (NOAA, JAMSTEC, NOC, GEOMAR) deploy permanent and semi-permanent observatories on the ocean floor to monitor seismic activity, temperature, salinity, chemical composition, and biological activity. These observatories require electrical power and data communication cables rated for 10–30 year continuous subsea immersion in depths ranging from 100 metres (shallow continental shelf) to 6000+ metres (deep ocean trenches).

The MT SUB E PLUS cable is specified for observatories operating in 0–300 metre depth ranges. For ultra-deep (>300 metre) observatories, Feichun offers custom enhanced variants rated to 1000+ metres using thicker sheaths and specialized armour systems.

Typical observatory power requirements are 50–500 kW (electrical power), transmitted via 6/10 kV or 12/20 kV submarine cable rated for seawater immersion. The MT SUB E PLUS cable meets this requirement, providing:

• Tinned copper conductors preventing corrosion during 20+ year immersion
• Per-phase copper braid shielding protecting against seawater ingress and EMI
• CR rubber sheath maintaining flexibility under deep-ocean conditions
• Dual AC/DC voltage ratings supporting DC power conversion in modern observatories

Underwater Robotics, ROV Systems & Subsea Intervention Equipment

Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), and tethered submersibles require power and control signals transmitted via umbilical cables from surface support vessels. For work depths up to 300 metres, the MT SUB E PLUS cable (in either power or data variants) provides the electrical backbone for subsea intervention:

• Power Delivery: Deep-diving ROVs may require 100–300 kW of electrical power for hydraulic pumps, lights, and manipulators. The MT SUB E PLUS 6/10 kV or 12/20 kV cable can deliver this power over distances up to 300–500 metres with acceptable voltage drop, supporting advanced subsea operations.
• Control Signal Integrity: The per-phase copper braid shielding ensures clean, low-noise electrical signals for control commands. In electromagnetically noisy offshore environments, this shielding prevents cross-talk between power and control conductors within the umbilical.
• Durability Under Continuous Use: Deep-diving operations involve repeated deployment cycles, with the cable subject to deck handling stress, saltwater immersion, and dynamic tensioning. The MT SUB E PLUS cable’s tinned copper and CR rubber withstand this cyclic duty, maintaining insulation integrity through hundreds of deployment cycles over a 10–15 year vessel operational lifetime.

Complete Technical Specifications Across Voltage & Current Ratings

(N)TSCGEWOEU MT SUB E PLUS — Available Configurations

(N)TSCGEWOEU MT SUB E PLUS 12/20 kV — Standard Conductor Sizes & Performance Data

Key Universal Specifications (Both Voltage Classes)

• Standard: DIN VDE 0250-813 (with reference to)
• Conductor Material: Tinned Copper (Class 5 = Flexible)
• Insulation: Rubber EPR 3GI3 (ethylene propylene rubber)
• Field Control Layers: Inner + Outer semiconducting rubber layers
• Protective Conductors: Copper wire braid over each phase (per-phase shielding)
• Outer Sheathing: Chloroprene Rubber (CR) 5GM3 (~5 mm thickness)
• Sheath Colors: Red or Black (red standard for marine identification)
• Flame-Retardant: VDE 0482-332-1-2 / IEC 60332-1-2 (self-extinguishing)
• UV Resistance: ISO 4892-2 (xenon arc exposure testing; for deployment/surface storage)
• Oil Resistance: EN 60811-404 Class A (mineral oils, hydraulic fluids)
• Ozone Resistance: VDE 0473-811-403 / IEC 60811-403
• Outdoor Use: Yes (specifically engineered for marine/subsea environments)
• Max. Conductor Temperature: 90 °C (continuous operation)
• Max. Short-Circuit Temperature: 250 °C (transient; allows protective device coordination)
• Operating Temperature (Fixed Installation): −40 to +80 °C
• Operating Temperature (Moving/Deploying): −25 to +60 °C
• Bending Radius (Moving Application): 10 × Outer Diameter
• Maximum Depth Rating: 300 metres saltwater immersion
• Expected Service Life: 15–20 years in continuous seawater immersion @ 300 m depth

Subsea Installation, Deployment & Maintenance Protocol

Pre-Deployment Cable Inspection & Preparation

Before deploying the MT SUB E PLUS cable in marine environments:

• Visual Sheath Inspection: Examine the CR rubber outer sheath for cracks, cuts, abrasion, or deformations. Minor surface marks (< 1 mm depth) are acceptable; deeper damage requires section replacement or full cable rejection.
• Insulation Resistance Baseline Measurement: Measure 1000 V insulation resistance from each conductor to ground, and between phase pairs. Record all baseline values. Accept only > 100 MΩ minimum. Baseline values typically range 500–2000 MΩ for new cable. Lower values indicate manufacturing defect or prior damage.
• Moisture Content Assessment: If cable has been stored > 6 months before deployment, perform moisture analysis on small insulation samples (test per IEC 60270). Accept moisture content < 0.1% (by mass). Higher moisture indicates water ingress during storage, suggesting potential subsea problems.
• Cable Reel Integrity: Verify cable reel structure is sound, proper cable lay is uniform, and the cable is tightly wound without slack or buckles.

Subsea Deployment Operations

Speed & Tension Control: Deploy the cable at moderate speed (0.3–1 m/s), controlling tension via a deck tensioner system. Avoid sudden stops or starts, which could create shock loads and sheath damage. Monitor cable tension continuously; do not exceed manufacturer recommendations (typically 500–2000 kg depending on conductor size).

Route Planning & Obstacle Avoidance: Pre-survey the subsea route using ROV or sonar to identify rocks, wreckage, coral, and other hazards. Plan the cable route to avoid sharp edges and high-current regions that could cause mechanical or thermal stress.

Depth Monitoring: Monitor cable depth continuously during deployment. Ensure the cable does not exceed 300 metres depth unless special enhanced variants are specified.

Post-Deployment Commissioning

After deployment to final seabed location:

• Insulation Resistance Re-Test: Measure 1000 V insulation resistance again. Expect slight decrease from baseline (typically 10–30% reduction) due to temporary moisture absorption during deployment. Accept any result > 10 MΩ. Values < 1 MΩ indicate potential installation damage; investigate before energizing.
• High-Voltage Test (Optional): Some projects perform 5–10 minute AC voltage withstand test at 70% of factory test voltage (e.g., 12 kV AC for a 17 kV factory-tested cable) before permanent energization. This confirms mechanical integrity of the installed cable.
• Thermal Stability Test: Run the cable at 25–50% rated current for 1–2 hours and monitor conductor temperature via infrared imaging from the surface (if ROV-based thermal camera is available). Temperature should rise to 50–70 °C and stabilize; no oscillations or unexpected increases. This confirms proper cooling and heat dissipation at operating depth.

Ongoing Maintenance & Monitoring

Annual Insulation Resistance Trending: At least annually (or as maritime regulations require), perform 1000 V insulation resistance measurements from each conductor to ground. Plot results on a trend chart. Insulation resistance should remain stable or slightly increase over time (typical range 5–1000 MΩ after initial deployment). A continuous downward trend (insulation resistance declining >50% year-over-year) indicates advancing degradation; consider cable replacement within 2–3 years.

Visual Inspection via ROV (Periodic): Every 3–5 years, deploy an ROV to visually inspect cable terminations, burial, and routing. Look for evidence of anchor drag, abrasion, or biofouling. Maintenance action is required if the cable is exposed to mechanical damage risk or if terminations show corrosion.

Environmental Compliance & Ocean Protection Standards

The MT SUB E PLUS cable is engineered to minimize environmental impact and comply with international ocean protection regulations:

Materials & Environmental Toxicity

• No Toxic Additives: The cable’s tinned copper, CR rubber, and EPR insulation are formulated without hexavalent chromium (Cr(VI)), polychlorinated biphenyls (PCBs), or other persistent organic pollutants banned under international marine agreements (MARPOL, Basel Convention, Stockholm Convention on Persistent Organic Pollutants).
• Biodegradable Packaging: Cable is wrapped in compostable biodegradable film during shipment, minimizing plastic waste impact.
• End-of-Life Recycling: After 20+ year service life, the cable is fully recyclable. Copper conductors and braid are recovered via smelting; CR rubber can be ground and reused in industrial applications. No toxic residue remains after recycling.

Electromagnetic Pollution Mitigation

The per-phase copper braid shielding and outer tinned copper braid reduce electromagnetic radiation from the cable, minimizing potential impact on marine organisms sensitive to electromagnetic fields (certain fish and marine mammals use electromagnetic sensing for navigation). The 85+ dB shielding effectiveness confines the cable’s EM field to a tight radius around the cable, preventing far-field radiation.

Compliance with Marine Protected Area (MPA) Requirements

Many regions require cables in Marine Protected Areas to minimize seabed impact. The MT SUB E PLUS cable’s flexible design allows it to be laid directly on soft seabed (mud, silt) without damage, rather than requiring burial or rigid conduit protection. This minimizes disturbance to sensitive benthic ecosystems.

Technical FAQ: Extreme Seawater Environment Scenarios

Q: Can the MT SUB E PLUS cable withstand full submersion in seawater for 20+ years without sheath damage or water ingress?

A: Yes, with proper installation. Long-term immersion testing (ASTM B117 salt spray applied to subsea conditions) confirms the cable maintains full electrical and mechanical integrity for 15–20 years in continuous 300-metre seawater immersion. Key conditions: (1) cable is properly terminated with sealed glands to prevent connector-induced water intrusion, (2) cable route avoids sharp rocks or coral that could abrade the sheath, (3) cable is not subjected to mechanical stress (anchoring, trawler-net impact, etc.), (4) annual insulation resistance monitoring shows stable or slightly improving trends. Under these conditions, the cable performs as designed.

Q: What happens if the MT SUB E PLUS cable is accidentally exposed to depths > 300 metres?

A: Beyond 300 metres, external pressure (>30 bar) begins to exceed design safety margins. Progressive effects: 300–400 m: cable remains operational but sheath compression increases, shortening projected service life by 20–30%. 400–500 m: sheath compression becomes severe; insulation may develop voids from pressure cycling; insulation resistance may decline faster than normal. >500 m: cable is at risk of sheath rupture or catastrophic electrical failure. If temporary over-depth exposure occurs (< 1 hour), the cable typically recovers when returned to shallower depth with no permanent damage. If prolonged (days to weeks) over-depth operation occurs, immediate replacement is recommended.

Q: Is the MT SUB E PLUS cable suitable for HVDC (high-voltage DC) transmission in marine renewable energy systems?

A: Yes. The cable carries dual AC/DC voltage ratings: 6/10 kV AC cable is rated 9 kV DC; 12/20 kV AC cable is rated 18 kV DC. The EPR 3GI3 insulation, field-control layers, and CR sheath are all rated for sustained DC operation. Practical DC applications include: (1) HVDC power transmission from offshore wind/tidal farms to mainland (using custom HVDC export cables with MT SUB E PLUS core), (2) DC-coupled energy storage systems where batteries store tidal/wave energy and release it via DC cables at night when renewable generation is low. The cable’s DC ratings make it compatible with emerging DC-coupled marine renewable systems expected to dominate after 2030.

Q: How does saltwater galvanic corrosion affect the tinned copper conductors over time, and can it be prevented?

A: Tinned copper is inherently resistant to chloride-induced galvanic corrosion compared to bare copper. However, long-term galvanic interaction with other metals in the subsea environment (steel anchors, iron-based seabed infrastructure) can slowly corrode even tinned copper if direct electrical contact occurs. Prevention: (1) ensure cable terminations use stainless steel or titanium hardware (never steel or aluminum) to avoid galvanic couples, (2) use insulating cable supports to prevent the cable from contacting dissimilar metals, (3) apply cathodic protection (sacrificial zinc or magnesium anodes) near cable terminations if the cable is in close proximity to large steel structures. With these precautions, tinned copper degradation is negligible over 20 years.

Q: What is the expected cost premium of the MT SUB E PLUS compared to standard terrestrial medium-voltage cables?

A: The MT SUB E PLUS carries a 25–40% cost premium over equivalent standard terrestrial cables, due to: tinned copper conductors (+3–5%), per-phase copper braid shielding (+8–12%), chloroprene rubber outer sheath (+5–8%), enhanced insulation formulation (EPR 3GI3, +3–5%), thicker sheath (+4–6%), specialized termination kits and installation procedures (+2–4%). However, in marine applications, the ROI is compelling: standard cables fail after 3–5 years in seawater (requiring replacement and emergency service calls costing $500K–2M), while the MT SUB E PLUS operates reliably for 15–20 years (single installation cost, no replacements). The premium is recovered within the first 3–4 years of operation.

Q: Can the MT SUB E PLUS cable be armoured for ultra-deepwater (>300 metre) applications, or does custom engineering become necessary?

A: Standard MT SUB E PLUS is rated to 300 metres. For 300–1000 metre depths, Feichun offers custom enhanced variants with additional armour: a layer of steel or aluminum wire armour applied over the outer sheath provides mechanical protection and spreads external pressure more evenly. With armour, depths up to 1000 metres become practical. Beyond 1000 metres, further design enhancements (thicker insulation, higher-grade field-control materials, specialized pressure-balanced core) are required. Custom engineering is case-specific; contact Feichun with your depth and deployment requirements for a tailored solution.