Parallel Circuits: Definition & Examples

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  • 0:00 Intro to Electrical Circuits
  • 1:40 What is a Parallel Circuit?
  • 2:50 Applying the…
  • 4:00 An Important Exception
  • 5:00 Another Example
  • 6:20 Lesson Summary
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Lesson Transcript
Instructor: Scott van Tonningen

Scott has a Ph.D. in electrical engineering and has taught a variety of college-level engineering, math and science courses.

In this lesson, learn more about parallel electrical circuits. We'll review some electrical circuit fundamentals, look at the defining characteristics of parallel circuits, and explore several concrete examples.

Intro to Electrical Circuits

Most power outlets in U.S. households provide electricity at between 110V and 120V. How is it that all these outlets can maintain the same voltage, even though there may be a number of appliances and components connected to them, all with different power consumptions? In your car, nearly every component that requires electricity (headlights, interior lights, radio, windshield wipers, etc.) runs on a constant 12 volts. How is this possible?

The answer lies in how the electrical circuits are wired. For these and many other electrical systems, the solution is to connect the circuit components in parallel.

What is a Parallel Circuit?

Before we get into a definition of a parallel circuit, let's do a quick review of some electrical circuit fundamentals, mainly voltage, current, resistance, and a few laws. Here are the ones that we'll need:

  • Voltage (V, in volts - V) is the electrical force responsible for making electrical charge move.
  • Current (I, in amperes - A) is a measure of the movement of electrical charge over time.
  • Resistance (R, in ohms) is a measure of how much a component opposes the movement of the current through it.
  • Kirchoff's Current Law (KCL) is simply an affirmation that charge must be conserved, and so the sum of the currents going into a circuit node (a point in the circuit where two or more components are connected) must equal the sum of the currents going out of the same node:


  • Kirchoff's Voltage Law (KVL) says that if you sum the voltages around any loop in a circuit, you will get zero:


Applying the Definition: Example

Let's start by looking at a technical definition of a parallel circuit. Two or more electrical components are said to be in parallel if the total electrical current flowing into the parallel network divides among the components then recombines to the same total current afterward. Now this may not seem to be the most intuitive definition, so look at the implications. A parallel circuit will have the following defining characteristics:

  • It starts with two or more components connected together in a circuit
  • Each of the components must have only two electrical contacts (wires, conduction paths, etc.)
  • The components are connected in such a way that they all share the same node on each side of the component
  • The voltage across all the components connected in parallel is the same
  • The current flowing into the parallel connection is the same as the current flowing out and is equal to the sum of the individual currents flowing through each component

Let's picture this practical definition as follows:

Electrical components connected in parallel
Parallel circuit example

The voltage across all three components (V) is the same and the KCL equation for either node (top or bottom) is the same, thus all three components are in parallel:

Summation of currents

Applying the Definition - Another Example

When trying to decide whether several circuit elements are in parallel, you can't just look at how the circuit is drawn; you must use the electrical characteristics of a parallel circuit. Here is an example:

Circuit with some components not connected in parallel
Circuit with some elements not in parallel

Which components form a parallel circuit? Only components #1 and #2, because both of them meet the following three conditions:

  • They share the same nodes at each of their connection points
  • They each have exactly the same voltage (V) across them
  • The current flowing into the two components separates into I1 and I2 and then recombines afterward

We cannot say that either component #3 or component #4 is in parallel with #1 and #2 because they don't share the same nodes on each side and the individual voltages across these components must have values that are less than V. We can show this by using the KVL equation for the loop that contains components #2, #3 and #4. Let V3 and V4 be the voltages across components #3 and #4, respectively. Then:

KVL equations for example

If V3 and V4 are not zero (exceptions are given in the next section) then they must be less than V.

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