Why Do The Positive And Negative Wires Spark When Touched?

Electrical Technology

Why Do The Phase And Neutral or Positive and Negative Wires Spark When Connected Together?

When positive and negative conductors touch, it produces a spark. Same is the case when phase and neutral wires make a contact. This scenario is known as a short circuit, which occurs when an unintended connection is made between two points having different electrical potential.

In the case of a short circuit (when the positive ⨁ terminal of a battery makes contact with the negative ⊖ terminal or the phase wire touches the neutral wire), a high current starts to flow due to the potential difference between the two points. This high voltage ionizes the air between the two conductors. During the process of air ionization, molecules lose electrons, creating a hot, glowing, and electrically conductive plasma.

The free electrons are attracted to the positive ⨁ terminal, while the ions are attracted to the negative ⊖ terminal. During the transition of ions and electrons through the plasma, they collide with each other as well as with air molecules between the terminals. Heat and light are produced during these collisions, which is observed as a spark in the case of short circuits.

The intensity of the produced spark depends on the level of voltage and current. The higher the voltage or current flowing in the circuit, the stronger the spark that will be produced.

Warning: Sparking wires are dangerous and may ignite hazardous fires or cause electric shocks. Therefore, it is advised never to touch live wires while working with electricity.

Let’s see why the spark ignite during the short circuit

Electrical Potential Difference: Positive and negative wires represent different electrical potentials (voltages). Same is case in Phase and Neutral wire in AC circuits. When they touch and make a contact between these two wires, the high potential difference causes a large current to flow rapidly between them.
Rapid Current Flow: The electrical current seeks the path of least resistance. When the wires touch directly, there is no resistance or electrical load between these two wires. Hence, they create a very low-resistance path, causing a sudden surge of current.
Energy Release: The rapid current flow generates heat and light energy. The heat can be intense enough to ionize the air around the contact point, creating a visible spark.
Material Properties: The materials of the wires (usually copper or aluminum) can vaporize at the point of contact due to the heat, contributing to the spark.
Circuit Conditions: If the circuit is powered, especially with a significant voltage and current capacity, the energy released when the wires touch can be substantial, resulting in a larger spark.

For example:

Suppose a phase (hot) and neutral wire touch while they are supplied from a single-phase, 50kVA, 230V transformer. We know that theoretically, the voltage becomes almost zero in the case of a short circuit. If we assume the voltage to be 1V (to avoid an infinite value), the amount of current flowing between those two wires would be extremely high.

I = P ÷ V ….. (∴ P = V × I)

Where:

I = Current in Amps
P = Power in Watts
V = Voltage in Volts

Putting the values:

Current in Amps = I = 50kVA ÷ 1V

Current in Amps = I = 50kA

This high amount of current will instantly start to flow between the two wires, which are not capable of handling such a current. Consequently, it will produce a high spark and flames, leading to damage to the connected appliances or even a hazardous fire if proper protective devices such as circuit breakers and fuses are not installed.

With proper protective devices in place, when the high current surge occurs, the breaker will detect the overload and disconnect the circuit from the fault.

The same scenario applies to capacitors and batteries, where positive and negative terminals accidentally or intentionally make contact. If the power rating is high, an intense spark will occur immediately.

Safety Concerns

Fire Hazard: Sparks can ignite flammable materials.
Equipment Damage: Short circuits can damage electrical components and devices.
Personal Injury: Sparks can cause burns or electric shock.

Prevention

Insulation: Ensure wires are properly insulated.
Proper Connections: Use appropriate connectors and avoid loose wires.
Circuit Protection: Implement circuit breakers or fuses to prevent short circuits.

Always handle electrical systems with care and ensure circuits are de-energized before working on them.