A Complete Guide to Medium Voltage Cables (6kV to 36kV)
Hello there. If you are reading this, you are probably looking for a reliable power cable for a project. Maybe you are building a factory, setting up a wind farm, or upgrading a city power grid. You have come to the right place.
In the cable industry, we call cables that carry power between 6kV and 36kV “Medium Voltage” (MV) cables. They are the workhorses of the electrical world. They are not as small as the wires in your house, but they are not as massive as the giant cables that cross oceans.
I have been in this business for 20 years. I have seen many buyers make simple mistakes that cost them time and money. This guide is here to help you avoid those traps. We will talk about what these cables are, how to read the specs, and how to choose the right one for your needs.
What Exactly is a Medium Voltage Cable?
Let’s keep this simple. Electricity needs a path to travel. A cable is that path. When we talk about “Medium Voltage,” we are talking about the amount of pressure pushing that electricity through the wire.
Think of water in a hose. Low voltage is like a garden hose. High voltage is like a fire hydrant. Medium voltage is somewhere in between. It is strong enough to power big machines but safe enough to be buried underground in a city.
The most common voltages you will see are:
6/10kV (Often used in factories)
12/20kV (Common in cities)
18/30kV and 26/35kV (Used for longer distances)
If your project requires moving power from a substation to a large building or a wind turbine, you are likely looking for a cable in this range.
The Most Important Part: Understanding the Standards
When you ask for a quote, suppliers will ask: “Do you need IEC or BS standard?” This is the first question you must answer. If you get this wrong, the cable will not fit your system.
Here is the breakdown of the two main “languages” we speak in the cable world:
1. The IEC Standard (International) Most of the world uses this. It is based on the number 6.
6/10kV
12/20kV
18/30kV
26/35kV
If you are in Europe, Asia, Africa, or South America, you probably need IEC. The insulation thickness for these cables is designed to handle these specific voltages. For example, a 12/20kV cable usually has about 5.5mm of insulation.
2. The BS/AEIC Standard (North America & UK) This is a bit different. It is based on the number 5 and 15.
5kV Class (covers 2.4kV to 4.6kV systems)
15kV Class (covers 8.3kV to 13.8kV systems)
25kV Class (covers 14.4kV to 23kV systems)
35kV Class (covers 24.9kV to 34.5kV systems)
If you are shipping to the USA or Canada, do not buy an IEC cable. It will not work. You need an AEIC or ICEA standard cable. The insulation levels are different (100% vs 133% insulation levels).
Decoding the Cable Name (The Alphabet Soup)
Cable names look like a secret code. They are actually very logical once you know the secret. Let’s look at the most common model: YJV22.
Here is what those letters mean:
YJ: This stands for the insulation material. It means XLPE (Cross-linked Polyethylene). This is the best material for MV cables. It handles heat well and lasts a long time.
V: This stands for the outer jacket. It means PVC. It protects the cable from the sun and weather.
22: This stands for Armor. It means there is a layer of steel tape under the jacket.
So, YJV22 means: A cable with XLPE insulation, a PVC jacket, and Steel Tape Armor.
Why does the armor matter?
No Armor (YJV): Use this inside buildings or in tunnels. It is flexible but easy to damage.
Steel Tape (YJV22): Use this if you are burying the cable underground. The steel stops rocks from crushing the cable.
Steel Wire (YJV32): Use this for underwater or vertical shafts. The wires stop the cable from stretching or breaking under its own weight.
Key Technical Parameters (The Numbers That Matter)
You do not need to be an engineer to check a spec sheet. But there are four numbers you must check to ensure quality.
1. Conductor Resistance This tells you if the copper or aluminum is pure.
If the resistance is too high, the cable will get hot and waste energy.
Always check if the supplier is using “Class 2” compacted conductors. This makes the cable smoother and easier to install.
2. Partial Discharge (PD) This is a silent killer. It is a tiny spark inside the insulation that you cannot see. Over time, it eats away the cable until it fails.
The Rule: A good MV cable must have a PD level of less than 10pC (pico-Coulombs). If a supplier cannot test for this, do not buy from them.
3. Temperature Rating
Normal: 90°C. This is how hot the cable can get while running normally.
Short Circuit: 250°C. This is how hot it can get for a few seconds if there is a power surge. XLPE cables handle this very well.
4. Bending Radius You cannot bend a thick cable like a garden hose. If you bend it too tight, you break the insulation.
Rule of Thumb: The bend should be at least 15 times the diameter of the cable. If the cable is 5cm thick, your bend must be 75cm wide.
How to Choose the Right Size (Ampacity)
This is where most mistakes happen. You cannot just guess the size. You need to calculate the “Ampacity” (Current Carrying Capacity).
Imagine the cable is a highway. If you put too many cars (Amps) on a small road, you get a traffic jam (Heat). If it gets too hot, the cable melts.
Here is a rough guide for Copper Core YJV cables in the air:
Voltage | Size (sqmm) | Approximate Amps |
6/10kV | 50 sqmm | ~175 A |
6/10kV | 120 sqmm | ~300 A |
6/10kV | 300 sqmm | ~500 A |
12/20kV | 50 sqmm | ~165 A |
12/20kV | 120 sqmm | ~285 A |
Note: These numbers change if you bury the cable in the ground or if it is very hot outside. Always ask your supplier for a “Derating Factor” calculation.
Copper vs. Aluminum:
Copper: Better conductor, smaller size, more expensive. Best for tight spaces.
Aluminum: Cheaper, lighter, but needs to be thicker to carry the same power. Great for long distance overhead lines.
Common Problems and How to Fix Them
In my 20 years of sales, I have seen three main problems. Here is how you avoid them.
Problem 1: Water Trees Water can sneak into the cable and create little root-like structures in the insulation. This kills the cable.
The Fix: If you are near water or in a humid area, ask for “Water Blocking Tape” or “Longitudinal Water Blocking” . This is a special powder or tape that swells up if it touches water, sealing the leak.
Problem 2: The Jacket Cracks You install the cable, and six months later, the black outer skin is cracking.
The Fix: Check the material. Standard PVC is okay, but PE (Polyethylene) is much better for outdoor use. It resists UV rays and weather much better. If you are in a very hot place, ask for a special UV-resistant compound.
Problem 3: Wrong Voltage Class You bought a 12/20kV cable for an 18/30kV system.
The Fix: Always tell the supplier your System Voltage (what the grid is) and the Cable Voltage (what you are buying). They should match or the cable rating should be higher. Never go lower.
Final Thoughts: Quality is Safety
Medium Voltage is dangerous. If the cable fails, it can cause fires or power outages that cost millions.
When you talk to a supplier, ask them these three questions:
1.
“Can you send me the Type Test Report?” (This proves the design is safe).
2.
“Do you do Partial Discharge tests on every meter?”
3.
“Is the conductor resistance within IEC 60228 standard?”
If they say yes to all three, you are probably in safe hands.
We have been making these cables for a long time. We know that a good cable is not just about copper and plastic. It is about peace of mind. If you are unsure about your specs, send us a message. We are happy to help you check your design before you spend a dollar.