This question comes up in almost every cable specification meeting. The short answer: there is no single global definition. Different standards bodies draw the line at different places, and that ambiguity can cause real headaches during project execution.

Three Standards, Three Different Answers

The practical consensus: below 2,000V is low voltage, above 35kV is high voltage, and everything in between is medium voltage. The gray area sits between 1kV and 2kV, where the classification depends entirely on which standard governs your project.

The Real Answer: It Depends on Where Your Project Is

For engineers and procurement teams, the academic debate matters less than knowing which standard applies to your specific installation.

US projects (IEEE/NEC framework): Medium Voltage Cable starts at 2,000V. The most common cable ratings you will encounter are 5kV, 8kV, 15kV, 25kV, and 35kV. For nuclear power plants, keep in mind that IEEE 1186-2025 now extends the medium voltage ceiling to 46kV.

International projects (IEC framework): Medium voltage typically starts at 1kV. Standard ratings include 3.3kV, 6.6kV, 11kV, 22kV, and 33kV. For example, Australian standard AS/NZS 1429.1 covers cables ranging from 1.9/3.3kV all the way to 19/33kV.

Solar and renewable energy projects: System voltages typically fall between 1kV and 35kV. The two most common levels are 15kV (matching 12.47kV or 13.8kV grid interconnection) and 35kV (matching 34.5kV).

Three Critical Parameters You Must Check

Cable voltage ratings are usually marked as Uo/U, for example 6.35/11kV. Here is what each number means:

Do not just look at the cable's "voltage class" and assume it fits. Match Uo to your system's phase-to-ground voltage, and U to your system's phase-to-phase voltage. Getting this wrong is one of the most common causes of premature cable failure.

Shielded vs. Unshielded: When Is It Mandatory?

Another question that follows closely: at what voltage do I need shielded cable?

For any cable operating above 5kV, shielding is not optional. The metallic shield equalizes electric field stress, carries fault current, and protects against electromagnetic interference. IEEE 1816-2024 dedicates an entire standard to proper termination and splicing of shielded cables from 2.5kV to 46kV, emphasizing that workmanship on terminations is often more critical than the cable itself.

A Quick Decision Guide

The Bottom Line

Medium Voltage Cable starts somewhere between 1kV and 2.5kV, depending on which standard your project follows. For US projects, the practical answer is 2,000V. For IEC-governed projects, it is 1kV.

What matters more than the threshold is this: understand your system's actual Uo/U values, confirm the shielding requirement, and pay as much attention to termination workmanship as you do to the cable specification. The most expensive cable in the world will fail prematurely if the joint is poorly made.