Overhead vs Underground Power Cables: Key Differences, Applications and Selection Guide

1. What Are Overhead Power Cables?

Overhead power systems transmit electricity through conductors installed above ground and supported by poles or towers.

Depending on the voltage level and application, overhead systems may use AAC, AAAC, ACSR and other overhead conductors, while covered or insulated designs can be used where additional protection is required.

Common overhead conductor types

AAC (All Aluminium Conductor) is commonly used where high electrical conductivity and relatively low weight are required, particularly in shorter spans and distribution applications.

AAAC (All Aluminium Alloy Conductor) uses an aluminium alloy construction that provides good mechanical strength and corrosion resistance.

ACSR (Aluminium Conductor Steel Reinforced) combines aluminium strands with a steel core to provide greater tensile strength, making it suitable for longer spans and higher mechanical loads.

Overhead insulated cables add insulation or protective covering around the conductor and can be used in distribution networks where improved protection against accidental contact and environmental exposure is required.

2. What Are Underground Power Cables?

Underground power cables are installed below the ground, typically directly buried or placed inside ducts, conduits or tunnels.

Modern underground systems commonly use copper or aluminium conductors with XLPE insulation, together with metallic screens, water-blocking components and optional armour depending on the voltage level and installation environment.

For medium- and high-voltage applications, cable construction may include:

• Copper or aluminium stranded conductor
• Conductor screen
• XLPE insulation
• Insulation screen
• Metallic screen or sheath
• Water-blocking layers where required
• Armour for specific installation conditions
• PE or PVC outer sheath

This construction allows underground power cables to operate in demanding environments while protecting the electrical system from external mechanical and environmental influences.

3. Overhead vs Underground Power Cables

The two systems serve the same fundamental purpose—transmitting and distributing electrical power—but their installation methods and operating characteristics are different.

These characteristics should be evaluated together rather than choosing a cable type based on one factor alone.

4. Installation and Construction Considerations

Installation conditions are one of the most important factors when selecting between overhead and underground systems.

• Overhead systems
• Overhead power networks generally require:
• Poles or transmission towers
• Crossarms and hardware
• Insulators
• Conductors
• Stringing equipment
• Suitable right-of-way

The construction process can be relatively straightforward when the required corridor is available.

However, the project may need to consider road crossings, buildings, vegetation, wind loading and other obstacles.

Underground systems

Underground installations generally require additional civil engineering work, such as:

• Excavation
• Cable trenches
• Duct systems
• Cable tunnels
• Backfilling
• Cable joints and terminations
• Drainage and thermal considerations

For this reason, underground power cable projects often involve higher installation complexity.

However, once installed, the cables remain protected below ground and have little visual impact.

5. Cost Considerations

Cost is an important factor in any power infrastructure project.

In many applications, overhead power systems have lower initial installation costs because they do not require extensive excavation, trench construction or underground duct systems.

Underground power cables can require substantially more civil engineering work. The total project cost may include excavation, ducts, cable protection, jointing systems, traffic management and reinstatement of roads or other surfaces.

However, comparing only the initial installation cost may not provide a complete picture.

A project evaluation should also consider:

• Expected service life
• Maintenance requirements
• Land and right-of-way costs
• Environmental conditions
• Accessibility
• Outage consequences
• Future expansion
• Urban development requirements

For critical infrastructure, the total project lifecycle should be considered rather than cable purchase price alone.

6. Reliability and Environmental Exposure

Overhead conductors are directly exposed to the surrounding environment. Wind, storms, ice, vegetation and other external conditions can affect the network.

For example, strong winds can cause mechanical stress on conductors and supporting structures, while falling trees or branches can affect distribution networks.

Underground power cables are less exposed to these surface environmental conditions. Their installation below ground can provide additional protection against weather-related disturbances.

However, underground systems are not maintenance-free. Cable faults can be more difficult to locate, and repairs may require excavation or specialized testing equipment.

Therefore, reliability depends not only on whether a cable is installed overhead or underground, but also on cable design, installation quality, operating conditions and maintenance practices.

7. Urban vs Rural Applications

The surrounding environment can strongly influence cable selection.

Urban power distribution

In densely populated cities, underground power cables can help reduce the use of overhead corridors and minimize visual impact.

They can be used for:

• Urban power distribution
• Commercial buildings
• Residential developments
• Underground utility networks
• Transportation infrastructure
• Industrial facilities

Limited space and high land utilization can make underground installation practical despite its higher construction complexity.

Rural and long-distance networks

Overhead systems are commonly used where large transmission corridors are available and long-distance power delivery is required.

Applications include:

• Rural electrification
• Utility distribution
• Long-distance transmission
• Substation connections
• Regional power networks

In these situations, overhead conductors such as AAC, AAAC and ACSR can provide different combinations of conductivity, mechanical strength and weight.

8. Underground Power Cable Selection

When an underground installation is required, selecting the appropriate cable construction is essential.

Several factors should be considered.

Voltage rating

Determine whether the project requires a low-voltage, medium-voltage or high-voltage cable.

The cable's rated voltage must match the operating requirements of the electrical network.

Conductor material

Copper conductors provide high electrical conductivity and can offer advantages where compact cable dimensions or high current capacity are important.

Aluminium conductors have lower density and can provide a lighter-weight alternative for many power distribution and transmission applications.

The selection should consider current capacity, cable size, installation conditions and overall project economics.

Insulation

XLPE insulation is widely used for modern medium- and high-voltage power cables because it provides suitable electrical and thermal characteristics for many power transmission and distribution applications.

PVC and EPR insulation may also be used depending on voltage level, environmental conditions and applicable specifications.

Armour and protection

Armoured power cables can provide additional mechanical protection where cables are exposed to potential physical damage.

For direct burial, industrial facilities, construction areas and other demanding environments, the appropriate armour and sheath construction should be determined according to the installation requirements.

9. When Should You Choose an Overhead Power Cable?

An overhead system may be considered when:

• A suitable right-of-way is available
• Long-distance transmission is required
• Installation speed is important
• Initial infrastructure cost needs to be controlled
• Easy visual inspection is valuable
• The surrounding environment permits overhead construction
• Mechanical and environmental loading can be appropriately managed

For overhead distribution, the choice between AAC, AAAC, ACSR and overhead insulated cable should be based on electrical load, span length, mechanical requirements, environmental conditions and network design.

10. When Should You Choose an Underground Power Cable?

An underground system may be considered when:

• The project is located in a densely populated urban area
• Available overhead space is limited
• Visual impact needs to be minimized
• The cable route passes through developed areas
• Additional protection from surface environmental exposure is required
• The project requires underground transmission or distribution
• Future urban development makes overhead infrastructure difficult to maintain

Underground systems can be particularly relevant to urban power grids, industrial facilities, renewable energy projects and infrastructure developments.

11. Overhead vs Underground: It Depends on the Project

There is no single cable installation method suitable for every power project.

An overhead network may provide practical advantages where long-distance transmission, accessible maintenance and lower initial infrastructure costs are important.

An underground network may be more appropriate where space limitations, urban development, environmental exposure and visual impact are major considerations.

The decision should therefore consider the complete project environment, including:

Voltage → Load → Route → Installation method → Environment → Mechanical protection → Maintenance → Lifecycle cost

A proper engineering assessment can help determine the most suitable cable construction and installation method.

Conclusion

The choice between overhead and underground power cables is an important decision in the design of modern power transmission and distribution networks.

Overhead systems can provide practical solutions for utility distribution, rural electrification and long-distance transmission, with conductors such as AAC, AAAC and ACSR serving different electrical and mechanical requirements.

Underground power cables, particularly XLPE-insulated copper or aluminium cables, provide solutions for urban networks, industrial projects and other applications where underground installation is preferred.

Rather than focusing only on cable price, project teams should evaluate voltage level, current capacity, installation environment, mechanical protection, maintenance requirements and lifecycle considerations. The right cable solution is ultimately the one that matches the technical and operating requirements of the specific project.