Electrical Conductor Sizing: Best Design Practices

Correct sizing of electrical conductors is a critical aspect in the design of electrical systems, instrumentation and telecommunications, as it directly impacts the efficiency, safety and reliability of the facilities. An inadequate selection of conductors can lead to energy losses, overheating, operational failures and serious electrical risks. In this article, we explore the applicable regulations, the main risks, the best design practices, the key aspects and the most common errors in this process.

Key Regulations

The design and sizing of electrical conductors must comply with international and local regulations that establish technical and safety criteria. Some of the most relevant standards include:

International Regulations

IEC 60364 - Low voltage electrical installations.
NFPA 70 (NEC - National Electrical Code) - Reference electrical code in the USA.
IEEE Std 399 (Brown Book) - Industrial electrical systems design.
IEC 60287 - Calculation of current carrying capacity of conductors.
IEEE Std 835 - Guide for sizing electrical cables.
IEC 60502 - Medium voltage cables (1 kV to 30 kV).
IEC 60947 - Protective and switching equipment.
BS 7671 - Electrical Installation Regulations in the United Kingdom.
IEC 61363 - Electrical systems in marine installations.
ISO 50001 - Energy efficiency in electrical systems.

Local regulations

NCh Elec 4/2003 - Low voltage installations in Chile.
Technical Regulations for Electrical Installations (RETIE, Colombia) - Safety in electrical installations.
Standard NOM-001-SEDE (Mexico) - Mexican electrical code.
IRAM 2183 (Argentina) - Electrical conductors in industrial installations.

Risks Associated with Incorrect Sizing

Poor design in the sizing of electrical conductors can lead to serious problems in the installation and affect the safety of personnel and equipment. The main risks include:

1. Overheating and Fire Risk

If a conductor is undersized for the current it must carry, high thermal dissipation will occur, which can lead to melting of the insulation, short circuits and even electrical fires.

2. Excessive voltage drops

The use of conductors with an inadequate section causes voltage losses at the ends of the installation, affecting the performance of electrical equipment, motors and sensitive electronic systems.

3. Energy Losses and Low Efficiency

A conductor with a smaller gauge than required increases the resistance in the circuit, which generates energy losses and high operating costs due to higher energy consumption.

4. Failures in Sensitive Equipment

In instrumentation and telecommunications systems, incorrect sizing can lead to interference, electrical noise and malfunction of control and monitoring devices.

5. Risks of Electric Shock

Overheating or insulation failures due to poor sizing can lead to ground faults, increasing the risk of electric shocks and affecting the safety of operators.

Best Practices for Conductor Sizing

To ensure a safe and efficient installation, it is essential to apply the following practices in the design and selection of electrical conductors:

1. Determine the Current Capacity

Use the current capacity tables of the applicable regulations (IEC, NEC, NCh Elec 4/2003).
Consider correction factors for ambient temperature, cable grouping, and insulation type.

2. Evaluate the Allowable Voltage Drop

It is recommended not to exceed 3% voltage drop in lighting circuits and 5% in power systems.
Calculate the voltage drop using the equation:

V = I×L×R

where:

I = Current in amperes.
L = Length of conductor.
R = Resistance of the conductor per unit length.

3. Consider Environmental Conditions

Ambient temperature and humidity affect the current carrying capacity of cables.
In industrial environments with the presence of chemicals or humidity, suitable insulation (XLPE, EPR) must be selected.

4. Select the Right Type of Insulation

PVC (Polyvinyl chloride): General use, temperature up to 70°C.
XLPE (Cross-linked polyethylene): Greater thermal resistance (90°C) and dielectric.
EPR (Ethylene Propylene): High chemical and moisture resistance applications.

5. Implement Overload and Short Circuit Protection

Design the system with appropriate protective devices such as fuses and circuit breakers.
Check coordination with the electrical system interruption capacity.

Common Errors in Conductor Sizing

Despite the importance of a good design, there are recurring errors that can compromise the efficiency and safety of the installation:

1. Not Considering the Length of the Conductor

Increasing the distance increases the resistance of the cable, which can cause excessive voltage drops.

2. Underestimating Correction Factors

Failure to apply correction factors for ambient temperature or cable grouping may lead to incorrect current rating.

3. Use of Low Quality Drivers

Using cables with low-quality aluminum alloys instead of certified copper can affect the conductivity and safety of the system.

4. Not Evaluating Future Expansion

Designing an electrical system without considering future loads can lead to costly oversizing or the need to replace conductors at short notice.

5. Ignoring Electromagnetic Compatibility (EMC)

In control and telecommunications systems, the use of unshielded conductors or incorrect routes can generate interference that affects system performance.

Conclusion

Proper sizing of electrical conductors is a critical factor to ensure the efficiency, safety and reliability of electrical, instrumentation and telecommunications installations. Applying appropriate regulations, assessing risks, following best practices and avoiding design errors is key to optimizing the performance of electrical systems. At Acciomate Engineering & Projects , we have the experience and technical knowledge to design electrical solutions that meet the highest standards, ensuring efficient, safe projects that are aligned with current regulations.