Open circuit and short circuit are two special terms that represent opposite extremes that the resistance number line.

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We can look at a circuit by spring at any type of pair that exposed terminals:


In the context of any two terminals that a circuit:

A short circuit indicates that the two terminals space externally connected v resistance R=0, the very same as an ideal wire. This method there is zero voltage difference for any kind of current value. (Note that actual wires have non-zero resistance!)

An open circuit indicates that the two terminals space points are externally disconnected, which is tantamount to a resistance R=∞. This way that zero existing can flow between the two terminals, regardless of any type of voltage difference. (Note that really high voltages can cause arcs of present to flow also over large air or vacuum gaps!)


open Circuit and Short Circuit

modify - Simulate

The concept of looking right into two terminals that a circuit and looking at the behavior at these 2 extremes is a powerful one.

In both theory and practice, words “externally” has actually no particular meaning. It’s an arbitrary boundary to separate the “original” habits of a circuit native the new behavior once we make certain modifications at any kind of pair the nodes. This artificial boundary considers the rest of the circuit, the parts internal to the black box, to be unmodified. By making that assumption, we have the right to make just one small change exterior to the black color box and see its impact on the black box.

Use in valuable Measurement

An appropriate voltmeter is open up circuit. An open circuit is a limiting approximation because that a actual voltmeter, i m sorry will have actually some big (but no infinite) resistance.

An right ammeter is quick circuit. A brief circuit is a limiting approximation for a real ammeter, i beg your pardon will have actually some tiny (but not zero) resistance.

See the Multimeters & measurements section because that more.

Use in Theoretical Analysis

Just together a voltmeter and ammeter measure by connecting 2 probes come a circuit, theoretical analysis is often completed by looking at simply two nodes that a circuit.

Open and also short circuit carry out two valuable points on the V-I curve.

In particular:

The open circuit voltage is the voltage difference measured between two terminals when no current is drawn or supplied.The short circuit current is the current that flows as soon as the terminals are compelled to have zero voltage difference.

We’ll use these two values in Thevenin Equivalent and Norton tantamount Circuits.

Use in robust Design

In useful design, we’d choose the circuits we build to survive both the normal problems they room designed for, and also some unusual problems that occur occasionally yet should no be enabled to reason permanent damage.

Open circuits happen even when undesired. Because that example, whenever other is disconnected or unplugged, we have actually an open up circuit condition.

Short circuits additionally happen also when undesired. Because that example, if a connector momentarily shorts throughout two terminals as it’s gift inserted, or a tiny metal shaving end up in the wrong place, we’ll have a short circuit condition.

Where possible, we should style for open and short circuits to occur at various places within the circuit, especially at any exposed inputs and also outputs. We should architecture such that any type of failures are temporary and/or recoverable, such as with a circuit breaker.

Use in Manufacturing

Intentional R=0Ω resistors (short circuit) room sometimes included to a printed circuit board due to the fact that the designer wants the versatility to adjust the worth without having to redesign the published circuit board later on if they want to include some nonzero series resistance (or other collection component) in the future.

Similarly, intentional jumper pads (open circuit) room sometimes included because the designer wants the versatility to affix a section later, perhaps to add a parallel resistance.

Both of these can permit for flexible alters while sharing the same manufacturing overhead costs. This keeps unit costs low and avoids high value redesign time.

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What’s Next

In the next section, Thevenin Equivalent and also Norton tantamount Circuits, we’ll see just how the two-terminal concept can be used to making a streamlined approximation of whatever is in the “black crate circuit” labeled above.