Understanding the Dangers of High Voltage Wires: A Technical Explanation

Your initial statement about electricity requires a path to earth to be dangerous or deadly is not accurate. While it's true that electricity needs a path to return to its source, the role of earth in dangerous electrical events is more about providing a pathway for current to flow through the body. Let's break down this concept with a technical yet understandable approach.

Basic Principles of Electricity

Electricity, when it flows through a circuit, needs a complete path from the source to the return. This path is why we often hear about "return" current being a crucial part of a circuit. Think of the simple circuit of a flashlight: a battery, a switch, and a lightbulb. There's no need for a path to the earth here since the current flows back to the battery.

AC Circuits and Household Wiring

In household applications in the US, we use alternating current (AC) which works similarly. Take the example of a typical doorbell. It runs on 24 VAC, supplied by a transformer. The transformer's secondary winding provides power to the doorbell, but the current leaves and returns via the same pathway.

For residential home wiring, things get slightly more complex. There is a utility transformer at the power company, or possibly at a pole, that steps down the voltage to 240 VAC between the two "line" wires. At the center of this, a "center tap" provides a 120 VAC power supply. This center tap is connected to earth ground, referred to as the "neutral" conductor, at both the circuit breaker box and the transformer. At the breaker box, it connects to ground rods and any other conductive surfaces that might come into contact with electricity.

Why Earth Becomes a Pathway

The earth is not a collection point for electricity but can become a path for current when a circuit is interrupted. If a live "hot" wire comes into contact with a grounded surface, it creates a 'short circuit.' This bypasses the usual path back to the transformer, creating a path of low resistance through the earth ground. The high current flow can lead to tripped circuit breakers and can also make the grounded surface safe by redirecting the current.

Electrocution and Current Flow

Electrocution occurs when current flows through the human body, completing a circuit. This is why touching high voltage wires can be deadly. The body provides a path for the current to flow from the wire, through the body, and back to the source. This can disrupt vital functions like the heart or damage internal organs, leading to electrocution.

Key Concepts Through Analogies

To understand the flow of current, consider an analogy with water. Water can flow through a pipe (the circuit) and back to a source. If the pipe is broken, water flows from a higher to a lower elevation, mimicking how current flows from a higher to a lower potential. Ohm's Law and Joule's Law help quantify this: Ohm's Law (V IR) tells us about the relationship between voltage, current, and resistance, while Joule's Law (P I2R) explains the power dissipated as heat.

Electrical Energy and Its Effects

Electrical energy, like any other form of energy, does work and can be damaging. It is the amount of power over time (watt-seconds or joules) that can cause harm. Significant current flowing through the body for a prolonged period can lead to fibrillation of the heart or cell death in vital organs, leading to permanent damage or death.

If a person is shocked, they should be safely removed from the source and taken to a hospital, even if they seem fine. Internal organ damage may not be immediately apparent and can worsen over time.

Resources for Further Reading

The document IEC TS 60479–1 “Effects of current on human beings and livestock.” is an excellent resource for in-depth technical information on the subject.

This explanation should clear up the connection between current flow and the danger of touching high voltage wires. If you have any more questions or need further clarification, feel free to ask!