Understanding Low, Medium, and High Voltage: Definitions and Applications

Introduction

In the complex and diverse world of electrical systems, the classification of voltage levels is crucial for safe operation and efficient design. The International Electrotechnical Commission (IEC) has established standards that provide definitions for various voltage categories, but these can vary significantly depending on the specific applications and industries involved. This article will explore the definitions of low, medium, and high voltage, with a focus on power distribution systems, on-site electrical systems, and low-voltage logic design.

Standard Definitions and Applications

The IEC 60038 standard offers a clear and simple classification of voltage levels, particularly in AC systems. According to this standard:

Extra Low Voltage (ELV): Anything below 50V Low Voltage (LV): 50V to 1000V High Voltage (HV): Anything above 1000V

These classifications are widely accepted in industries such as electric motor control, switchgear, and power distribution systems. However, it's important to note that these definitions can vary in specific contexts, as we will discuss further.

Voltage Classifications in Specific Fields

Logic Design Perspective

For logic designers, the classification of voltage levels is quite different and often involves lower voltage values. Common voltage levels in logic design are:

High Voltage: 1.8V, 3.3V, 5V

Automotive Engineering Perspective

From the perspective of automotive engineers, the voltage levels may be:

High Voltage: 12V, 42V, 400V

Power Systems Engineering Perspective

In power systems engineering, the voltage levels can be much more extensive:

High Voltage: 120V to 8000 to 30000V and above Medium Voltage: 120V to 600V and 2400 to 69000V Low Voltage: 120V and below

Voltage Categories in Power Distribution Systems

The classification of low, medium, and high voltage in power distribution systems is as follows:

High Voltage (HV): Extra-High Voltage (EHV) and Ultra-High Voltage (UHV) range from 115000 to 1100000VAC to 11000000 to 30000000VAC.

Medium Voltage (MV): 2400 to 69000VAC.

Low Voltage (LV): 240 to 600VAC

On-Site Electrical Systems

In on-site electrical systems, the voltage classifications are:

High Voltage: 1000 to 4160 volts

Medium Voltage: 50 to 1000 volts

Low Voltage: 0 to 49 volts

PCB Design Perspective

For Printed Circuit Board (PCB) designers, voltage classifications are typically:

High Voltage: Above 48V Medium Voltage: 16 to 47V Low Voltage: 15 and under

This classification is based on the risk and potential damage to the circuit.

Practical Voltage Classifications

The practical implications of these classifications can be illustrated as follows:

Low Voltage (LV): Typically 12V or less, with AC or DC voltage

Medium Voltage (MV): Houses and most small businesses use 120/240V and are almost always AC

High Voltage (HV): 600V or more, typically used by industrial customers and almost always AC

Publication of 7200V to 13.2kV is often used by utilities or very large industrial customers and is typically AC in nature

Distribution voltages between 34.5kV to 500kV are typically used for the bulk transmission of power between substations and are always AC.

Official vs. Unofficial Classifications

Here is a highly unofficial but commonly used classification for voltage shock sensation:

Low Voltage: You won't feel it. 50V Medium Voltage: You get a shock that makes you jump. ~ 100V High Voltage: You are dead soon after you touch it. 500V

While these unofficial classifications can be helpful for understanding the potential hazards, it's important to always follow proper safety protocols and guidelines when working with electrical systems.