Selección del Conductor Eléctrico

Spoiler: If you don't properly select electrical conductors and make a mistake, you might be building a future problem for your installations with the potential for fire… and that's not a good experiment.

When we think of electricity, we usually imagine lights turning on, motors spinning, or computers running. But behind all that modern convenience lies a critical question: are you using the correct electrical conductor for your installation?

And no, it's not just a matter of "putting a cable and that's it." Choosing wrong can have serious consequences: from energy inefficiency to devastating fires. In this blog, I want to take you through the technical, but also reflective, process of how to correctly select an electrical conductor. Because as in any good experiment, the details matter.

Why Does the Conductor Matter So Much?

Electrical conductors are the arteries of any electrical system. If you choose one too small, it overheats. If it's too large, you're wasting money and materials. And if you ignore the regulations… well, then we're in serious trouble.

In Colombia, for example, regulations such as RETIE, RETILAP and NTC 2050 V2 establish clear criteria. But beyond legal compliance, what's at stake is the safety, efficiency and durability of the system.

The Variables That Change Everything (And You Can't Ignore)

1. The Current That Will Flow

Everything starts with understanding how much current will flow through that conductor. The basic formula is simple:

I = P / V

• I: Current in amperes
• P: Power in watts
• V: Voltage in volts

But knowing the present isn't enough. You also have to think about the future: Do you plan to expand the installation? Add more equipment? Overload doesn't always happen on the first day.

2. The Voltage Drop

Did you know that a long cable can "steal" voltage from your equipment? As electricity travels, part of the energy is lost as heat due to the conductor's resistance.

The voltage drop must be kept within certain limits (generally 3% for lighting and 5% for other loads). If you exceed them, your equipment will malfunction or may not even start.

Basically, when electricity travels through a cable, part of the voltage is lost along the way. This loss is called "voltage drop."

Imagine voltage as the pressure water has in a pipe. The longer the pipe, the more pressure is lost before the water comes out at the end. The same thing happens with electricity.

The calculation equation for voltage drop is based on elementary principles of electrical physics, and its origin dates back to Ohm's laws and the electrical resistance of conductive materials. For this, we will consider the IEC 60364-5-52:2011 standard – "Electrical installations of buildings – Selection and erection of electrical equipment – Wiring system," and we will use the letters VD from the English term "Voltage Drop" or Delta V, and the equation we use is:

𝑉𝐷 = 𝛥𝑉 = 𝐼 × 𝑅 = 𝐼 × (𝜌 × 𝐿 𝐴 )

Where:

• ΔV = voltage drop (volts)
• I = current (amperes)
• R = conductor resistance (ohms)
• ρ = material resistivity (ohm·mm²/m)
• L = total length of the round-trip path (meters)
• A = cross-sectional area of the conductor (mm²)

And yes, that "R" depends on the cable material. Which leads us to the next question.

3. Copper or Aluminum: Which is Better?

• Copper: More expensive, but also more efficient and resistant to corrosion.
• Aluminum: More economical and lightweight, but with lower current-carrying capacity, plus requires extra care in connections.

The material affects not only conductivity but also weight and system lifespan. Choosing between one or the other is not a matter of preference, but of technical context.

4. What If It's Hot, Humid, or There Are Chemicals?

Environmental conditions change the rules of the game. A conductor in a food factory or a coastal area does not behave the same as one in an air-conditioned office. That's why insulation must adapt: flame-retardant, corrosion-resistant, or even armored if there is an explosion risk.

5. Type of Load: Not Everything Behaves the Same

• Resistive loads (like heaters): Predictable and stable.
• Inductive loads (motors): Can generate current spikes when starting.
• Electronic loads (computers, variable frequency drives): Generate harmonics that distort the signal and affect sizing.

Each type of load has its own "electrical footprint." And that footprint determines what the conductor that feeds it should be like.

The Step-by-Step Process: How is the Conductor Selected?

Step 1: Calculate the Maximum Current

We already said it, but it's worth repeating: without current, there is no selection. And without a good estimate, the system is doomed to error.

Step 2: Consult Ampacity Tables

The ampacity tables (like those in Article 310 of NTC 2050 V2) tell you how much a conductor can handle based on its material, insulation, and installation conditions.

Step 3: Check Voltage Drop

Don't assume everything is fine. You have to do the calculations. And if it doesn't meet the rules, increase the gauge.

Step 4: Apply Correction Factors

Ambient temperature and the number of conductors grouped together affect heat dissipation capacity. The base value must be corrected.

Step 5: Choose the Conductor Material

Copper or aluminum? Solid or stranded? THHN, XLPE, or halogen-free insulation? There is no single answer. It all depends on the environment.

Step 6: Don't Forget the Grounding Conductor

Yes, that cable that many see as an "accessory" is actually essential for safety. Consult table 250.102(C)(1) of NTC 2050.

Common Mistakes (That You Could Avoid)

1. Ignoring voltage drop
2. Forgetting environmental factors
3. Not applying grouping corrections
4. Not planning the installation for the future
5. Using poor-quality materials

And Could This Be Done Automatically?

Well, to a large extent, yes. Nowadays, technology gives us great possibilities to use software and applications that help us make better decisions and solidify data for the design and selection of materials in our installations. This is the case with CableApp, which is a free professional application from Prysmian to calculate the cross-section of low and medium voltage electrical cables for each type of installation, taking into account their economic and ecological sections, in accordance with current standards and regulations. This tool will allow you to calculate the total energy savings on your electricity bill and the annual CO2 emissions, providing possible alternative solutions from an optimal point of view, designed for professionals in the sector such as installers, consultants, engineers, and students.

In Summary

Choosing an electrical conductor is not just a technical calculation. It is an exercise in foresight, responsibility, and design. And as in any well-executed experiment, the variables matter, mistakes are costly, and well-founded decisions lead to success.

So next time you see an electrical cable, ask yourself: who chose it? Did they know what they were doing? And if not… what could go wrong?

Do you want a practical guide with real examples and simplified tables? Or do you have questions about how to apply NTC 2050 V2 in a real project? Let me know in the comments or write to me directly. Because understanding the science behind our technical decisions… that's what's truly electrifying.