Array & Export Cables
The array cables that string the turbines together and the export cables that carry the power ashore, laid on the seabed and buried into it. Cables are a small share of the capital cost and by far the largest share of the sector's failures.
Last updated 2026-08-24
Typical duration
One to two offshore seasons for a full array and export campaign, with manufacturing slots booked years ahead and the export cable alone capable of occupying a lay vessel for weeks.
What is Array & Export Cables?
Every turbine has to be connected to something. Array cables run from turbine to turbine in strings, each string gathering a handful of machines and terminating at the offshore substation. Export cables take the combined output from the substation to a landfall on the coast and onwards to an onshore substation and the grid connection point. It sounds simple and it is anything but, because a subsea power cable is a precision-manufactured object that has to be handled in enormous continuous lengths, laid along a route that has been engineered metre by metre, buried into a seabed that resists being dug, pulled up into a structure without ever being over-bent or over-tensioned, and then left alone for decades in an environment that includes anchors, fishing gear, mobile sand and its own thermal behaviour.
The single most important fact about offshore cables is this: they are the most common and most expensive cause of failure in the whole sector. A cable fault does not just cost the repair. It takes turbines or entire strings offline, sometimes for months, while a repair vessel is found, a spare length is located, the fault is precisely located on the seabed, the cable is cut, recovered, jointed and reburied. The claims history across the industry is dominated by cables, and almost all of it traces back to a handful of causes: cable left exposed because burial was not achieved, damage during pull-in, failure of the protection system where the cable enters a structure, and external impact from anchors or fishing. None of those are exotic. They are the predictable consequences of rushing the parts of the job nobody can see.
That is why so much of a cable campaign happens before any cable is loaded. The route is surveyed and engineered to avoid boulders, wrecks, existing services and unsuitable ground, and to cross what cannot be avoided under an agreed crossing design. A burial risk assessment establishes how deeply the cable needs to be buried along each part of the route to protect it against the threats that actually exist there - anchoring, fishing, mobile sediment, scour - and that assessment, not a rule of thumb, sets the target. The route is cleared of obstructions and, where necessary, surveyed for unexploded ordnance. Only then does the lay vessel arrive. Every tension limit, bend radius and burial target belongs to the cable supplier, the designer and the burial assessment, and they are the ones who own those figures.
Compare the methods at a glance
When and why is Array & Export Cables used?
Cable work overlaps the rest of the programme rather than following it. Array cables are often pulled into foundations as soon as the structures are available and long before the turbines they will serve exist, because pulling a cable into an empty foundation is far easier than working around a commissioning team. Export cables and their landfall are frequently the longest-lead element on the whole project: the manufacturing slot is booked years ahead, the onshore route needs its own consents and land agreements, and the landfall itself often has to be constructed in a specific season to respect environmental restrictions on the beach. The reason to take all of this seriously is disproportionate to the cost of the cable. Cables are a modest share of the capital budget and the dominant share of lost production and insurance claims, so the money and time spent on route engineering, burial and protection is the cheapest risk reduction available to the project. A turbine that fails costs one turbine. An export cable that fails can cost the entire wind farm.
Types of Array & Export Cables
Explore each method in depth - benefits, limitations, plant and quality control on its own page.
Array cables
Medium-voltage cables running turbine to turbine in strings, each string collecting a group of machines and running back to the offshore substation. Laid in relatively short lengths, they are handled many times over a campaign, which makes handling discipline the main quality issue. Because a single fault takes a whole string offline rather than one machine, the layout of the strings is itself a risk decision, and each cable end has to be pulled into a structure and hung off without breaching the supplier's limits.
Export cables
High-voltage cables carrying the entire output of the wind farm from the offshore substation to shore, often over a long route and in continuous lengths measured in tens of kilometres. They are manufactured to order in slots booked years in advance, transported on carousels aboard the lay vessel and jointed offshore where a single length cannot cover the distance. The whole project depends on them, so redundancy, burial and protection are treated with a seriousness that array cables do not always receive.
Landfall and shore crossing
The point where the export cable transitions from sea to land, usually through horizontal directional drilling from a compound behind the beach out to an exit point in the nearshore, so the cable passes beneath the intertidal zone without opening it up. Open-cut crossings are still used where drilling is impractical, but they need a working window that respects tides, seasonal environmental restrictions and public access. The transition joint bay behind the shoreline is where marine cable meets onshore cable and where both suppliers meet each other.
Cable protection and remedial burial
Where burial cannot be achieved or a cable approaches a structure, protection is added instead: rock berms placed from a fall-pipe vessel, mattresses, grout bags, half-shells or engineered cable protection systems at the structure entry. It is also the answer when a post-lay survey finds shallow burial, free spans or exposure. Remedial protection is normal and expected on any long route - what is not acceptable is discovering the need for it only after the cable has been in service for a winter.
Best suited for
- Collecting turbine output in strings and delivering it to a single offshore collection point
- Long export routes to shore where a buried cable is the only practical way to move the entire output of a wind farm
- Landfalls at sensitive or defended coastlines, where directional drilling avoids opening up the intertidal zone
- Routes with heavy anchoring or fishing activity, where deeper burial and engineered protection buy decades of reliability
Array & Export Cables: step by step
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Step 1: Survey and engineer the route
The route is designed, not chosen. Geophysical survey maps the seabed and shallow geology along a corridor, picking up boulders, sand waves, hard ground, wrecks, existing cables and pipelines and anything else that would stop a plough or a jetting tool. Geotechnical sampling establishes whether the ground can actually be trenched by the intended method, because a burial target that the seabed will not permit is a target that gets quietly abandoned at sea. A burial risk assessment then sets the required depth along each section based on the real threats there - anchoring, fishing activity, mobile sediment, scour near structures. The output is a route engineered metre by metre, with crossing designs agreed with the owners of anything the cable must pass over, and a clear statement of where burial will be achieved and where protection will be needed instead.
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Step 2: Clear the route before anything is laid
A cleared route is a cheap route. Boulders are removed or the alignment is adjusted around them, debris is recovered, and where the site history demands it the corridor is surveyed and cleared of unexploded ordnance under a specialist campaign with its own consents and controls. Pre-lay grapnel runs sweep the route for abandoned wire, netting and old cable that would otherwise wrap a plough or damage a cable during lay. Crossings are prepared in advance, typically by placing a separation layer over the existing asset so the new cable never bears directly on it. All of this happens with survey vessels and support spreads rather than the lay vessel, because the one certainty is that finding an obstruction with the cable vessel on site is the most expensive possible way to find it.
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Step 3: Manufacture, test and load the cable
Cables are made to order in continuous lengths, tested at the factory before they leave, and loaded onto the lay vessel's carousel or turntable in a controlled operation that itself has to respect the supplier's bend radius and tension limits. Loading a long export cable takes days and is monitored throughout, because damage introduced during loading travels out to sea inside a cable nobody can inspect. Electrical testing at the factory, after loading and at every subsequent stage builds a chain of evidence that the cable was sound when it left and sound when it arrived. Ancillaries travel with it: bend restrictors, bend stiffeners, hang-off arrangements, protection systems and the jointing kits that will be needed if a length has to be joined offshore.
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Step 4: Build the landfall and pull the cable ashore
At the coast, a compound is established behind the shoreline and a directional drill is used to form a duct from the compound out to an exit point in the nearshore, passing beneath the beach, any defence structure and the intertidal zone. The lay vessel positions offshore, the cable end is floated in or pulled through the duct by a winch line, and the pull is monitored continuously against the supplier's tension limits with the cable supported so it is never over-bent. Once ashore, the end is terminated in a transition joint bay where the marine cable is jointed to the onshore cable that continues to the substation. The landfall usually carries the tightest environmental conditions on the whole project, so the working window is fixed by the consent and the tides rather than by the contractor.
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Step 5: Lay and bury along the route
The lay vessel works along the engineered route paying out cable under controlled tension, following the alignment on survey, with the touchdown point monitored so the cable is placed where the design says and not in a slack loop somewhere near it. Wherever possible the cable is buried at the same time as it is laid, using a plough or a jetting or cutting trencher that opens a trench, sets the cable into it and allows the seabed to close over. Simultaneous lay and burial is preferred because it never leaves the cable exposed. Where ground or geometry prevents it, the cable is laid first and buried in a separate post-lay pass. Progress, tension, position and burial performance are logged continuously, and any section that fails to reach the target depth is recorded for treatment rather than left to be discovered later.
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Step 6: Pull in and terminate at each structure
Each cable end has to get from the seabed up into a foundation or the substation, and this is where a disproportionate share of the sector's failures are created. The end is recovered, rigged and pulled up through a J-tube or entry duct by a winch, guided by divers or a remotely operated vehicle, with the pull monitored against tension and bend limits throughout. A bend restrictor or stiffener protects the cable where it changes direction at the entry, and a cable protection system covers the exposed length between the seabed and the structure. Inside, the cable is hung off so its weight is carried by the structure rather than the conductor, and terminated by qualified jointers working to the supplier's procedure in clean, controlled conditions. Every one of those details has a failure history behind it, which is exactly why each one is inspected and recorded.
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Step 7: Protect, survey and prove the installation
Once cables are in, the route is surveyed to establish what was actually achieved: as-laid position against design, burial depth along the length, free spans, exposures and the condition of crossings and protection systems. Where burial fell short, remedial protection is placed - rock berms, mattresses or shells - to bring the section up to the level the risk assessment requires. Electrical testing is repeated after installation to confirm the cable survived the process, and the results are compared with the factory records. The as-built survey then becomes the baseline for the whole operational life: every future inspection is measured against it, and the first survey after a winter is where the project finds out whether the sediment stayed where the designers thought it would.
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Step 8: Notify, protect and hand over to operations
A buried cable that nobody knows about is a cable waiting to be hit. Positions are notified to the authorities that publish navigational information, cable awareness charts are updated, and the operator engages with fishing and shipping interests so anchoring and trawling risks are understood rather than assumed. Protection zones may be applied for where the risk justifies it. Internally, the handover pack brings together route surveys, burial records, test results, jointing records and the location of every joint and every protected section, because when a fault eventually occurs the repair team will start by reading exactly these documents. Monitoring systems - including temperature and strain sensing built into the cables themselves - are commissioned so that the operator can see the cable behaving rather than wait for it to fail.
Plant & equipment
- Cable-lay vessels with carousels or turntables, tensioners and controlled pay-out systems
- Ploughs, jetting trenchers and mechanical cutting trenchers for simultaneous and post-lay burial
- Remotely operated vehicles and diver spreads for pull-in, inspection and touchdown monitoring
- Winches, quadrants, rollers and pull-in spreads at structures and at the landfall
- Horizontal directional drilling rigs and shore compounds at the landfall
- Fall-pipe rock placement vessels and mattress-handling spreads for protection and remedial burial
- Survey vessels with multibeam, sub-bottom profiling and cable tracking equipment
- Grapnel runs, boulder clearance grabs and unexploded ordnance survey and clearance spreads
Quality control & testing
- Factory acceptance testing before despatch, repeated after loading, after lay and before energisation
- Continuous monitoring of tension and bend radius against the cable supplier's stated limits during every handling operation
- As-laid position surveyed against the engineered route, with deviations recorded rather than absorbed
- Burial depth verified along the whole length and compared against the burial risk assessment target
- Pull-in records for every cable end, including tension logs, restrictor installation and protection system fitting
- Jointing and termination carried out by qualified jointers to the supplier's procedure, in controlled conditions, with full records
- Crossing installations inspected by remotely operated vehicle and recorded against the agreed crossing design
- Post-installation electrical testing compared with the factory baseline before the cable is accepted
Safety watchpoints
- Cables under tension store enormous energy, and a parted line or wire snapping back is unsurvivable in the wrong place
- Overside and splash-zone operations during pull-in, with people working close to moving loads over water
- Diver and remotely operated vehicle operations near live vessels, thrusters and moving cable
- Unexploded ordnance risk on many seabed routes, managed by survey and specialist clearance before any work begins
- Crossings of existing live cables and pipelines, where damage is both a safety event and a third-party incident
- Landfall works combining drilling operations, tidal working areas and public access to a beach
- High-voltage terminations and the strict discipline between installation work and any energised system nearby
- Weather and sea state limits set by the vessel and the marine warranty surveyor, with a defined point at which lay is suspended and the cable end is safely laid down
Common defects to hunt
- Burial short of the target depth, leaving sections exposed or in free span and vulnerable to anchors and trawl gear
- Damage during pull-in from exceeding the supplier's tension or bend radius limits
- Failure or wear of the cable protection system where the cable enters a structure - one of the most widely reported problems in the sector
- External damage from anchors, fishing gear and dropped objects on routes where the risk was underestimated
- Faults at joints and terminations, often traced back to conditions or workmanship during a rushed offshore operation
- Cable movement in mobile sediment, so a cable buried correctly on day one becomes exposed within a season
- Abrasion at crossings where the separation layer was inadequate or displaced
- Manufacturing defects that pass factory testing and only appear under service load, which is why baseline test records matter
How long does Array & Export Cables take?
Typical duration: One to two offshore seasons for a full array and export campaign, with manufacturing slots booked years ahead and the export cable alone capable of occupying a lay vessel for weeks..