The Ultimate Guide to Choosing the Right Cable for Submarine and Underwater Installations
If you work in marine engineering, offshore oil and gas, or underwater robotics, you know that water is the enemy of electricity. A standard cable might work fine on land, but drop it into the ocean, and it becomes a liability.
I have spent the last 20 years helping clients solve cabling nightmares. The most common question I get is simple: “Why did my underwater cable fail?”
Usually, the answer is that the cable wasn’t built for the specific type of water pressure or movement it faced. In this guide, we are going to strip away the complex jargon. We will look at exactly what makes a cable survive underwater, how to read the specs, and how to stop your equipment from short-circuiting in the deep sea.
Why Standard Cables Fail Underwater
You cannot just take a regular power cable and throw it into the ocean. It will not last. Water is heavy, corrosive, and it finds every tiny weakness in a cable jacket.
When a standard cable goes underwater, three main things happen:
1.
Water Treeing: This is a fancy term for moisture sneaking into the insulation. Over time, tiny water branches grow inside the plastic. Eventually, they touch the wire, and boom—short circuit.
2.
Corrosion: Saltwater eats metal. If your armor or conductor isn’t protected, it will rust or dissolve.
3.
Hydrolysis: This is when the plastic jacket itself breaks down because of a chemical reaction with water. Cheap PVC jackets turn into mush after a few months in the sun and sea.
To stop this, you need a cable designed with a “barrier” mindset. We need to stop water from getting in, both from the side (radial) and from the ends (longitudinal).
The Armor: Steel vs. Aramid
When you order a submarine cable, the first decision is protection. We call this “armor.” You need armor because the ocean floor is rocky, and fishing nets can snag your cable.
There are two main types of armor we use for underwater jobs:
Galvanized Steel Wire: This is the heavy-duty option. If your cable is sitting on the bottom of the ocean (static), use steel. It stops sharks, rocks, and anchors from cutting your power. It is strong, but heavy.
Aramid Yarn (Kevlar): This is for moving cables. If you have a Remotely Operated Vehicle (ROV) diving and surfacing, steel is too heavy and stiff. Aramid is a synthetic fiber that is stronger than steel but very light. It floats and bends easily.
Pro Tip: Never use steel armor for a moving ROV. The steel will fatigue and snap. Always use Aramid for dynamic (moving) applications.
The Jacket: Why PUR Beats PVC
On land, we use PVC (Polyvinyl Chloride) for everything. It is cheap and works well. Underwater, PVC is a disaster. It gets soft in heat and brittle in cold.
For submarine installations, we almost always recommend PUR (Polyurethane) or HDPE (High-Density Polyethylene).
PUR: This is the gold standard for underwater cables. It resists saltwater, oil, and abrasion. It stays flexible even in freezing water. If you are dragging a cable over a sharp reef, PUR will survive. PVC will shred.
HDPE: This is great for cables that sit still on the ocean floor. It is very hard and has great water resistance, but it is stiff.
If you want your cable to last 10+ years, pay the extra money for a PUR jacket. It saves you money on replacements later.
Understanding Water Blocking Technology
This is where most manufacturers cut corners. A cable needs to stop water from traveling down the wire like a straw. We call this “Longitudinal Water Blocking.”
Imagine you cut the cable. If water gets in that cut end, it can travel up the wire for miles if not stopped.
We use two methods to stop this:
1.
Water Swellable Powder/Tape: Inside the cable, we pack a special powder. If water touches it, it turns into a gel instantly. It plugs the hole and stops the water from moving further.
2.
Metal Sheath: For deep sea cables, we wrap the core in lead or copper. This creates a 100% waterproof wall. Water cannot pass through metal.
For most commercial underwater projects, the swellable powder method is sufficient and keeps the cable flexible.
Technical Specifications Table
When you are looking at a datasheet, ignore the marketing fluff. Look at these specific numbers. I have put together a “Cheat Sheet” for a standard high-quality underwater cable below.
Feature | Specification | Why It Matters |
Conductor | Tinned Copper (IEC 60228 Class 5/6) | Bare copper rusts. Tin plating stops rust and makes soldering easier. |
Insulation | XLPE (Cross-Linked Polyethylene) | Better than rubber. It handles heat and resists water treeing. |
Jacket Material | Polyurethane (PUR) | Tough. Resists oil, salt, and tearing. |
Water Blocking | Swellable Tape & Powder | Plugs leaks automatically if the jacket is cut. |
Armor | Galvanized Steel or Aramid | Steel for static (floor), Aramid for dynamic (moving). |
Voltage Rating | 0.6/1kV up to 35kV | Ensure it matches your power supply. |
Min. Bending Radius | 6x Cable Diameter | Don’t bend it tighter than this, or it will break. |
Temperature Range | -40°C to +90°C | Works in freezing arctic water or hot tropical seas. |
Dynamic vs. Static Applications
One of the biggest mistakes engineers make is buying a static cable for a dynamic job.
Static (Fixed) Cables: These are cables that go into the water and never move. Think of a cable running from an offshore wind turbine down to the sea floor. These cables need heavy armor and thick jackets. They are designed to stay there for 20 years.
Dynamic (Moving) Cables: These are for ROVs, dredgers, or underwater cameras that get pulled up and down. These cables need to be “torsion balanced.” This means when you pull them, they don’t twist. If a cable twists while being pulled up, it will kink and destroy the copper inside.
If you are building an ROV, you need a cable that can handle millions of bending cycles. Do not use a wind turbine cable for a robot; it will fail in a week.
Common Installation Mistakes to Avoid
Even with the best cable, bad installation kills the connection. Here are the top three errors I see in the field:
1.
Ignoring the Bend Radius: Every cable has a limit on how tight it can turn. If you force a thick cable around a small wheel, you crush the insulation. Check the spec sheet for the “Minimum Bending Radius.”
2.
Bad Termination: The cable might be perfect, but if the connector (the plug) isn’t sealed right, water gets in. Use proper resin kits or vulcanized splices. Never just use electrical tape underwater.
3.
Dragging Over Sharp Edges: PUR is tough, but it isn’t magic. If you drag a cable over a sharp steel deck edge, it will cut. Use cable rollers or sheaves to guide the cable into the water.
How to Extend the Life of Your Submarine Cable
You want your equipment to last. Here is how you get the most life out of your underwater cable:
Rinse with Fresh Water: Salt is corrosive. After every job, rinse the cable with fresh water to remove salt crystals.
Check for Jacket Damage: Before every dive, look for nicks or cuts in the PUR jacket. If you see the armor, replace the cable.
Store on a Reel: Never pile the cable on the floor. Keep it on a reel to prevent kinks.
Keep it Dry: When storing, cap the ends. Moisture in the air can still get into the conductor strands if left open for months.
Final Thoughts
Choosing a cable for submarine or underwater installations is not about finding the cheapest option. It is about risk management. A 500cablethatfailsandcausesa500 cable that fails and causes a 50,000 equipment loss is the most expensive cable you ever bought.
Focus on Tinned Copper, PUR Jackets, and proper Water Blocking. If you get these three right, your system will run smoothly, whether it is in a shallow lake or the deep ocean.
If you are unsure about your specific setup, always ask for a custom calculation. Don’t guess with water.