Open Circuit vs Short Circuit : Differences and Examples

The understanding of open circuit vs short circuit will help us to analyze both extreme conditions in our circuit along with its risk and dangerous condition.

What is an Open Circuit?

What does it mean if we have an open circuit?

Just like its name implies, an open circuit is an electrical circuit that has an “open” path, a “hole”, “not-closed”, or in other name, a “disconnected” circuit. An open circuit is a circuit when it has a disconnected terminal or point.

Just like what we have learnt about electrical current, the main point for an electrical current to flow in the circuit is it shall provide a path from positive polarity to negative polarity. The path should not have any hole along its path.

A disconnected circuit is the same with a broken circuit since its electrical path is broken.

But keep in mind that not every open circuit is an accident. Sometimes we intendly make the circuit have an open path. The most common example of this purpose is a switch to turn off a lamp.

Since the switch is open, our circuit does not have a closed path, hence no electrical current is flowing to the lamp.

For our study here, we will use a DC circuit for easier explanation.

For better understanding, observe the circuit below.

Here we have a circuit with a two-points terminal, a and b.

The open circuit is the pair of terminals that are externally disconnected from each other. Because they are not connected, there is no electrical current flowing through them.

Compared with a “normal” circuit on the right.

The circuits above show us the open circuit resistance. An open circuit voltage is the voltage measured across a pair of terminals when there is no electrical current flowing through them. In this path, there is no electric current drawn from the source.

We can use Ohm’s Law to make this easier.

Since there is no electric current, we put I = 0 A, thus

It is the same if we do the opposite

Where R is ∞ thus

What conclusion can we get from this simple calculation?

We can conclude that an open circuit will not cause any injury or serious problem since there is no electrical current to harm its surroundings. The only thing we must take caution is not to accidentally connect these open terminals with anything, especially our body parts.

Even if there is no electric current flowing through the open terminals, the voltage still exists, up to the maximum voltage supplied by the source.

But an open terminal does not always mean that our electrical circuit will turn off. It depends on our circuit configuration to make it functional even if we intentionally or not, make a hole in our circuit path.

In a series circuit, an open terminal will make the electric current unable to flow through the circuit. As an example, imagine a flashlight circuit which is easily made by a battery, a switch, and a light, all connected in series.

Once the switch is open, the electric current is cut off, the lamp does not glow.

What about an open parallel circuit?

When a parallel circuit has an open terminal on one of its branches, the electric current will flow to another closed circuit branch. Of course, the consequence is the closed circuit branches will have higher current flowing through them.

What is a Short Circuit?

What does a closed look like?

The opposite of an open circuit is a closed circuit. A closed circuit is a circuit where there is no disconnected point, disconnected terminal, or broken path.

Both short circuit and closed circuit share the same principle. So what is the difference between short circuit and closed circuit?

Short circuit is a closed circuit where there is no load in that circuit.

When we are talking about no load, it means our circuit only has a source with a closed path conductor, connecting the positive polarity of a source to its negative polarity directly.

Use an open circuit below to make it easier to imagine a closed circuit.

A short circuit is a pair of terminals that are externally connected to each other. Because they are connected directly only with a conductor wire then there is zero voltage across them.

Why is the resistance zero? A short circuit current is a current flow through a pair of terminals with zero voltage difference.

In an ideal condition, a short circuit has exactly zero resistance since there is no load installed in the circuit.

But in the real circuit, it still has very low resistance from the conductor wire.

For now, let us use the ideal condition. Assume that R = 0, then

What can a short circuit cause?

Short circuits cause high current flowing in the circuit and may damage it. Not only that, if it has a high voltage source then it will produce a large amount of electric power or heat or even a fire. Our electrical devices can be broken and any conductor wires can be melted.

Keep in mind that in the practical field, a conductor wire has non-zero resistance. It can be very low resistance but not exactly zero.

What if we have a short circuit in a series circuit?

A short series circuit is not different with a closed switch. It will act as a conductor wire to carry electrical currents.

What if we have a short circuit in a parallel circuit?

Opposite from the short series circuit, a short parallel circuit means we put a conductor wire in a parallel connection in the circuit.

Remember that current will likely choose a path with the least resistance as its flowing path. The lower the resistance in a branch, the more current will flow through that branch.

If we use an ideal short circuit then the resistance on that branch will be zero and the current will be infinite.

The equivalent resistance the circuit above is

Difference Between Short Circuit and Open Circuit

An open circuit is a disruption in electrical current flow since it prevents it from flowing through the circuit while an open circuit is a huge electrical current flowing through a near zero resistance circuit path.

Both open circuit and short circuit can be considered as circuit failures. But two of them have different characteristics.

In an open circuit, the current flowing in the circuit is zero. On the other hand, in a closed circuit, the current flowing in the circuit is very high (infinite).

The resistance in an open circuit is very high (infinite), while a short circuit has very low resistance (zero).

The voltage drop across the open circuit terminal is equal to the voltage source. Across the short circuit terminal, the voltage drop is zero since the resistance is zero.

The summary between open and short circuit can be observed from the figures below.

Even though these two are considered harmful, we can make use of these extreme conditions to make something.

An ideal voltmeter is an open circuit which has very large resistance (not infinite).

An ideal ammeter is a closed circuit which has very low resistance (not zero).

Summary of Open Circuit vs Short Circuit

An open circuit means a break in our electrical path, there is no electric current flowing through it.

An open circuit has infinite resistance and no electrical current.

A short circuit means a very low resistance path that can produce abnormally high current to flow in our circuit. The lowest resistance path is the shortcut used by the electric current to flow.

A short circuit has near-zero resistance and high electrical current flow.

Key differences:

• Electrical current flow : no electrical current to flow in an open circuit, while a huge electrical current will flow in a short circuit.
• Resistance : an open circuit has infinite resistance, while a short circuit has near zero resistance.
• Cause : open circuit can be caused by broken component, connection, wire, or open switch. A short circuit can be caused by broken insulation.
• Example : an open circuit is a flashlight circuit turned off by opening the switch. A short circuit is a frayed electrical cord where exposed wires touch.

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