In the world of electrical engineering and power distribution, medium voltage cables play a vital role in transmitting electricity between substations, transformers, and industrial sites. 

Among these, 11kV and 33kV cables are two of the most commonly used voltage grades. Understanding the difference between 11kV and 33kV cables is crucial for project engineers, utility planners, and purchasing managers in industries where safety, reliability, and compliance are essential.

In this guide, ZMS Cable will dive into the key differences between 11kV and 33kV cables, their construction, applications, advantages, and how to choose the right one for your project. 

Whether you're planning an industrial installation or managing a distribution network, this article offers valuable insights into medium voltage cable selection.

What Are Medium Voltage Cables?

Medium voltage (MV) cables are defined as cables that carry voltages ranging from 1kV to 35kV, depending on the national or industry standards. They are used to distribute power over relatively long distances in both public utility networks and industrial environments.

Common medium voltage levels include:

6.6kV

11kV

22kV

33kV

MV cables are designed to handle higher stress levels than low voltage cables and typically feature specialized insulation and armor for protection in harsh conditions.

Overview of 11kV and 33kV Cables

11kV Cable

An 11kV cable is rated for systems operating at 11,000 volts. It is frequently used in regional distribution networks, feeding electricity from substations to commercial and industrial zones.

Typical uses of 11kV cables:

Power transmission in urban and suburban areas

Transformer-to-switchgear connections

Medium-sized industrial plants

Underground or overhead distribution systems

33kV Cable

A 33kV cable handles voltages up to 33,000 volts and is primarily used for transmitting electricity over longer distances or from power plants to high-capacity substations.

Typical uses of 33kV cables:

Transmission in rural and semi-urban areas

Renewable energy projects (solar/wind farms to the grid)

Inter-substation connections

Industrial zones requiring higher load capacity

Key Differences Between 11kV and 33kV Cables

While both cables fall under the medium voltage category, they differ in several critical areas:

1. Voltage Rating

11kV cables operate at a lower voltage, typically 6.35/11kV (phase/phase-to-earth).

33kV cables operate at a higher voltage, generally rated at 19/33kV.

This impacts the insulation level, thickness, and overall design of the cable.

2. Insulation Thickness

11kV cable insulation is generally 3.4mm thick (as per IEC or BS standards).

33kV cable insulation can be 8mm or more, depending on standard requirements.

The increased insulation in 33kV cables is essential to withstand higher electrical stress.

3. Conductor Size

33kV cables often have larger conductors than 11kV to handle higher loads and longer distances.

Common conductor sizes:

11kV: 70 mm2 to 300 mm2

33kV: 95 mm2 to 630 mm2

4. Overall Cable Diameter and Weight

Due to thicker insulation and larger conductors, 33kV cables are significantly larger and heavier than 11kV cables. This affects installation costs, trenching requirements, and handling procedures.

5. Cost

33kV cables are more expensive due to:

More copper/aluminum content

Thicker insulation

Higher-grade semiconducting materials

Greater quality assurance in manufacturing

Estimated cost difference:
A 33kV cable may cost 1.5 to 2 times as much as an 11kV cable of equivalent length and conductor size.

6. Applications and Usage Environment

11kV cables are ideal for localized power distribution within towns, campuses, and factories.

33kV cables are better suited for intermediate transmission between substations, or for powering large infrastructure or renewable energy projects.

Typical Construction of Medium Voltage Cables (11kV vs 33kV)

Common Standards for 11kV and 33kV Cables

Medium voltage cables are manufactured to meet various international and regional standards. Here are some common ones:

IEC 60502-2 – For power cables with rated voltages from 6kV to 30kV

BS 6622 / BS 7835 – British Standard for armored MV cables

IS 7098 Part II – Indian Standard for 3.3kV to 33kV cables

AS/NZS 1429.1 – Australian/New Zealand medium voltage cable standard

These standards dictate everything from insulation type and mechanical strength to flame resistance and testing protocols.

Applications: When to Use 11kV vs 33kV Cable

Choosing between 11kV and 33kV cables depends on the specific electrical design, power requirements, and layout of the project.

Installation Considerations

Bending Radius

33kV cables require larger bending radii, which can affect routing in trenches or ducts.

Jointing and Terminations

33kV joints and terminations are more complex and require highly trained personnel.

Special equipment is used to test insulation integrity before commissioning.

Thermal Performance

33kV cables often have higher current-carrying capacity, but derating factors like soil thermal resistance and cable grouping must be accounted for in both voltage grades.

Testing and Maintenance

Before commissioning, both 11kV and 33kV cables undergo high-voltage withstand testing and partial discharge testing. However, the testing voltage and duration differ:

11kV cable testing: 22kV AC for 5 minutes

33kV cable testing: 66kV AC for 5 minutes

Also, 33kV systems often require frequent inspections due to higher insulation stress and the risk of water treeing in XLPE insulation.

Environmental and Safety Concerns

Both cable types can be made with Low Smoke Zero Halogen (LSZH) sheathing for installations in enclosed or public areas to reduce toxic smoke in the event of a fire. UV-resistant and rodent-resistant jackets are also recommended for outdoor installations.

Final Thoughts: Which One Should You Choose?

The key difference between 11kV and 33kV cables is in their voltage rating, insulation requirements, size, cost, and intended use. 11kV cables are suitable for short-distance, moderate-load applications, while 33kV cables are used for longer-distance transmission and higher-capacity networks.

When selecting a medium voltage cable:

Consider your system voltage and load demand

Evaluate the installation environment

Factor in long-term maintenance and safety requirements

Always comply with local electrical codes and standards

If you're still unsure, consulting with a certified electrical engineer or cable manufacturer can help you choose the best solution tailored to your project’s needs.