High-voltage underground cable systems depend on more than the cable itself. The metallic sheath or screen surrounding an HV cable also forms part of the electrical system, and the way that sheath is bonded and earthed can directly influence cable losses, induced voltages, personnel safety and long-term reliability.

This is where the high voltage link box becomes an important part of underground cable design.

A link box provides an accessible connection point for cable sheath bonding and grounding. Depending on the bonding scheme, it can incorporate removable links for testing and maintenance and may also include Sheath Voltage Limiters, or SVLs, to control transient sheath voltages. Peace Power describes its Link Box, also referred to as a Disconnectable Link Box, as an essential accessory within high-voltage underground XLPE cable systems.

At Dutco Tennant, we support electrical infrastructure projects with solutions for underground cable networks, including HV cable accessories and link-box applications. For utilities, EPC contractors and consultants evaluating high voltage link box suppliers at Middle East Energy Exhibition, understanding the function of sheath bonding is a useful starting point before selecting a particular link-box arrangement.

Why HV Cable Sheath Bonding Matters

High-voltage power cables commonly include a metallic sheath or screen around the insulation.

This metallic layer performs important electrical functions, but it can also experience induced voltages when current flows through the conductor. If the sheath bonding arrangement is not properly designed, circulating currents may develop and create additional electrical losses.

A correctly engineered cable sheath bonding system is intended to manage these effects.

According to Peace Power, sheath bonding and earthing are used to:

  • minimise or eliminate circulating sheath currents;
  • reduce sheath power losses;
  • control induced sheath voltages;
  • protect personnel against touch and step voltages; and
  • provide a safe path for fault and short-circuit currents to earth.

The link box provides the physical interface through which these bonding and earthing connections are arranged.

What Is a Disconnectable Link Box?

A cable link box is an enclosure containing the electrical links and connections associated with the metallic sheaths of an underground cable circuit.

The term "disconnectable" refers to the removable links inside the enclosure.

These links allow individual cable sheaths to be disconnected from the bonding circuit when required for testing, inspection or fault diagnosis.

This is particularly valuable during commissioning and maintenance because engineers can isolate individual sheath sections without dismantling permanent cable connections.

Peace Power notes that these removable links support activities such as sheath-integrity testing, fault location and verification of sheath insulation after cable installation.

For long underground routes, this access can simplify the process of identifying the section requiring further investigation.

How Link Boxes Fit Into the Cable Protection System

An HV link box should not be considered an isolated enclosure installed beside a cable route.

Its internal connections are part of the complete cable sheath bonding circuit.

Peace Power states that its link boxes are mechanically and electrically integrated with the sheath-bonding circuitry of HV XLPE power cable systems and form part of the overall cable-protection arrangement.

This means the internal copper-bar arrangement and removable-link configuration need to correspond with the actual bonding design of the cable circuit.

The correct link box therefore depends on questions such as:

  • Is the cable sheath solid bonded?
  • Is single-point bonding being used?
  • Does the circuit use cross bonding?
  • Are SVLs required?
  • Is the box positioned at a termination or joint?
  • Will it be installed underground, on a wall or on a pedestal?

These design inputs should be established before the link box is finalised.

Solid Bonding: A Direct Sheath Connection

In a solid-bonded system, the cable sheaths are bonded and earthed at multiple points.

This arrangement helps keep sheath voltage relatively low because the metallic sheath remains connected to earth along the cable route.

However, the same arrangement can allow circulating currents to flow in the sheath during normal operation.

These currents can contribute to power losses.

For shorter cable runs or installations where circulating sheath current is acceptable, solid bonding may form part of the cable design.

A suitablelink box provides the necessary connection points for these sheath and earth conductors.

The final arrangement should always follow the project's cable-system study rather than being selected only from general application rules.

Single-Point Bonding Reduces Circulating Current

Single-point bonding takes a different approach.

The cable sheath is grounded at only one location, which prevents a closed metallic loop from forming and can therefore eliminate circulating sheath current.

The trade-off is that induced sheath voltage can increase toward the unearthed end of the circuit.

This is one reason a link box with SVL may be used in such a system.

Peace Power identifies single-point bonding as one of the main link-box configurations and notes that SVLs can be incorporated where required to control sheath voltages.

The exact bonding and SVL arrangement should be determined through the cable-system design and applicable voltage calculations.

Cross Bonding for Longer HV Cable Routes

Long underground HV cable circuits commonly require more advanced sheath-bonding arrangements.

Cross bonding divides the cable route into sections and cross-connects the metallic sheaths of different phases so that induced voltages can be balanced over the complete major section.

A cross bonding link box provides the connection point where these sheath conductors are transposed and cross-connected.

Peace Power notes that cross bonding is used to balance induced voltages and significantly reduce sheath losses.

This makes cross-bonding design particularly relevant where utilities need to manage efficiency across long cable routes.

Because the exact internal connections depend on the location within the bonding scheme, Peace Power engineers the copper-bar and link arrangement according to the project's sheath-bonding diagram.

What Does an SVL Do in a Link Box?

A Sheath Voltage Limiter is a protective device connected between the cable sheath and earth.

Under normal operating conditions, the SVL remains effectively non-conductive. When a transient overvoltage appears on the cable sheath, the device limits the voltage by providing a controlled path toward earth.

This can be particularly important during switching events, lightning-related transients or fault conditions.

A link box with SVL therefore combines the sheath-bonding connection with overvoltage protection for the cable sheath.

The SVL rating and arrangement should be selected according to the expected sheath voltage and the overall bonding design.

It should not be treated as an optional accessory added without calculation.

Why Fault Current Needs a Controlled Path

The cable sheath bonding system also has an important role during faults.

If an internal cable fault causes current to reach the metallic sheath, the bonding and earthing system needs to provide a controlled path for that fault current.

Peace Power states that its link boxes are intended to support safe diversion of fault and short-circuit current to earth through the bonding system.

This makes short-circuit performance an important part of link-box evaluation.

Peace Power publishes type-test information covering short-circuit current conditions including 50kA for one second, 63kA for one second and 40kA for three seconds, together with other electrical and enclosure tests.

Project teams should still confirm the required rating for their specific cable system.

Underground Link Boxes Need Suitable Environmental Protection

Many link boxes are installed in cable pits or underground chambers.

These environments can expose the enclosure to moisture, groundwater and contamination.

Peace Power offers underground-type link boxes designed for installation in dedicated concrete pits with accessible manhole covers. Wall-mounted and pedestal configurations are also available for different installation locations.

The company also lists IP65 and IP68 testing among its link-box type tests.

For an underground link box, environmental protection therefore needs to be considered alongside electrical performance.

Useful project information can include:

  • installation location;
  • expected water exposure;
  • cable-pit dimensions;
  • access requirements;
  • corrosion environment; and
  • required enclosure protection.

Wall-Mounted and Pedestal Designs Serve Different Locations

Not every link box needs to be installed underground.

Wall-mounted designs can be used in locations such as GIS halls, substations or on structural supports near outdoor cable terminations.

Pedestal-mounted versions can be installed in open outdoor areas where underground pits are unsuitable due to groundwater, soil conditions or accessibility.

This installation flexibility allows the high voltage link box to be positioned according to the actual cable route and bonding point.

The internal electrical design still needs to correspond with the bonding scheme regardless of enclosure arrangement.

Disconnectable Links Simplify Testing and Maintenance

One of the practical advantages of a disconnectable link box is the ability to separate sheath sections for testing.

During routine maintenance or fault investigation, engineers may need to test the integrity of the cable outer sheath.

Removing an internal link allows the relevant cable section to be electrically isolated from neighbouring sections.

Peace Power specifically identifies sheath-integrity testing, fault diagnostics and post-installation verification among the maintenance advantages of the disconnectable design.

For asset owners, this means the link box can support not only initial cable installation but also long-term condition assessment.

Where Are Link Boxes Typically Installed?

The correct location follows the sheath-bonding system design.

Peace Power identifies typical locations including:

  • insulated joint positions on long cable routes;
  • cable-circuit ends near terminations; and
  • designated cross-bonding points.

A route using several major cable sections may therefore contain multiple link boxes, each performing a different bonding function.

One box may provide straight bonding, another may contain cross connections, and another may include SVLs.

This is why link boxes should be scheduled against the cable route and sheath-bonding diagram rather than procured as identical standard boxes.

Link Box Selection Should Begin With the Bonding Scheme

For project teams evaluating a cable link box, the bonding scheme is one of the most important documents to review.

A useful technical enquiry should provide information such as:

  • system voltage;
  • cable type and construction;
  • cable length;
  • number of phases and circuits;
  • sheath-bonding method;
  • link-box position;
  • expected short-circuit current;
  • SVL requirement;
  • installation arrangement; and
  • environmental protection requirements.

This helps ensure that the internal link and copper-bar configuration corresponds with the design.

Peace Power states that each link box is engineered according to the applicable project-specific sheath-bonding scheme.

Why Link Boxes Matter for Cable-System Efficiency

Sheath bonding is often discussed in terms of protection, but it can also affect cable-system efficiency.

Circulating sheath currents create losses.

Where cross bonding or single-point bonding is appropriately designed, these currents can be reduced or eliminated, allowing more of the cable system's thermal capability to be used for transmitting load current.

This does not mean a link box itself increases cable capacity.

Rather, the correct cable sheath bonding arrangement helps control one source of cable-system loss.

For utilities operating heavily loaded underground circuits, these losses can be important to the overall thermal and electrical design.

Maintenance Accessibility Supports Long-Term Reliability

HV cable systems are expected to remain in service for many years.

Being able to inspect and test the sheath-bonding system during that operating life can therefore be valuable.

A well-designed link box should provide controlled access to the bonding connections while maintaining the required enclosure protection.

Clear identification of links and sheath connections can also help technicians work more confidently during maintenance activities.

This is one reason link-box engineering should consider operational access as well as initial installation.

Explore Peace Power Link Boxes With Us at Middle East Energy 2026

At Dutco Tennant LLC, we support electrical network projects with products and technologies for underground cable infrastructure. Our wider electrical portfolio includes high-voltage underground cable link boxes and related cable-network solutions.

Middle East Energy 2026 will take place from 1–3 September 2026 at Dubai World Trade Centre, UAE, and Dutco Tennant LLC will exhibit at Hall H5, Stand D10.

For professionals comparing electrical products at MEE Dubai, the exhibition provides an opportunity to discuss how link boxes fit into HV cable sheath-bonding systems, including solid bonding, single-point bonding, cross bonding and SVL arrangements.

Visitors with upcoming projects can bring their cable-system details, sheath-bonding diagrams, short-circuit requirements and proposed link-box locations for a more focused technical discussion.

A link box may occupy only a small part of an underground cable installation, but its role is significant. By providing accessible, project-specific bonding connections, it helps manage induced sheath voltages, circulating currents, fault-current paths and maintenance access across the cable system.

For long-term HV cable reliability, proper link-box selection and cable bonding arrangements are an important part of the overall system design, as discussed in our updates, the quality of the sheath-bonding design is therefore just as important as the cable itself.