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Parallel Circuits

As first-year industrial electricians you will encounter various types of circuits. In this lesson, we’ll break down one of the most common types you’ll face: parallel circuits.

Interactive Demo

Move the voltmeter to see how voltage is/isn’t affected.

How Parallel Circuits Work

In a parallel circuit, the voltage across each branch is the same, but the current can vary depending on the resistance of each branch. Here’s a simple formula to understand the total resistance (R_total) in a parallel circuit:

This formula shows that the total resistance is always less than the smallest individual resistor in the circuit.

What is a Parallel Circuit?

A parallel circuit is an electrical circuit where multiple paths are available for current to flow. Unlike a series circuit, where there is only one path, a parallel circuit allows electricity to travel through different branches. Each branch operates independently, so if one component fails, the others can still function.

Supermarket Checkout Lane Analogy

Imagine you’re at a busy supermarket with multiple checkout lanes. Each lane represents a different path for customers to leave the store. If one lane gets crowded or closes, customers can still check out through the other lanes. Similarly, in a parallel circuit, if one path is blocked or has a high resistance, the current can still flow through the other paths.

Water Flow Analogy

Think of a parallel circuit as a network of water pipes. Imagine a water tank with several pipes leading out of it. Each pipe represents a different path for water to flow. If you add more pipes, the water can flow more easily because there are more routes for it to take. In electrical terms, adding more resistors in parallel decreases the overall resistance, allowing more current to flow.

Practical Examples for Industrial Electricians

Example 1: Lighting Systems

In an industrial setting, you might encounter parallel circuits in lighting systems. For instance, multiple lights connected in parallel ensure that if one bulb burns out, the others continue to shine. This setup is crucial for maintaining consistent lighting in large industrial spaces.

Example 2: Motor Control

Consider a scenario where multiple motors are used to drive different conveyor belts in a factory. These motors can be connected in parallel to a single power source. This configuration ensures that each motor operates independently. If one motor fails, the others can continue running, keeping the production line moving.

Example 3: Heating Elements

In industrial processes, heating elements are often used to maintain specific temperatures. Connecting heating elements in parallel allows for better control and reliability. If one heating element fails, the others can still provide the necessary heat.

Example 4: Emergency Systems

Emergency lighting and alarm systems in factories are critical for safety. These systems are often wired in parallel to ensure that even if one path fails, the others remain operational. This ensures that all alarms can sound off, guiding everyone to safety.

Practice Problems

Problem 1: You have three resistors connected in parallel: R1 = 6 ohms, R2 = 12 ohms, and R3 = 18 ohms. Calculate the total resistance of the circuit.

Solution:

Problem 2: In a parallel circuit, you have two resistors: R1 = 10 ohms and R2 = 20 ohms. If the total voltage supplied to the circuit is 120V, what is the current through each resistor?

Solution:

The voltage across each resistor is the same (120V).

• Current through R1:

• Current through R2: