Open and short circuits are two special configurations that deserve special attention while learning basics of Electrical Engineering. Given below are the 5 differences between open and short circuits.
- Current passing through an open circuit is zero, while current through the short circuit is infinite.
- An open circuit posses infinite resistance, while a short circuit posses zero resistance.
- The voltage through the short circuit is zero, while voltage through the short circuit in maximum.
- An ohmmeter connected to short circuit displays ‘0’ ohms while an ohmmeter connected to open circuit displays ‘infinity’ or ‘0L’.
- Practically, short circuit happens when a low resistance wire connects across the circuit and an open circuit occurs when a circuit breaks from some point.
An open circuit is the one having a disconnection between components. The figure below displays an open:
A short circuit is the one where components are connected with a very small or zero resistance wire. The figure below displays an ideal short.
An open circuit posses infinite resistance, while a short circuit posses zero resistance.
Ω for open → Infinite
Ω for short → Zero
An ohmmeter connected across a short displays ‘0’ ohms or very small values of ohms. An ohmmeter across open will display 1 or 0L. (Most multimeter manufacturers display 0L for open).
Current always requires a path to flow. If it is open, no electrons will flow from one terminal to other and the resultant current will be zero. Similarly, resistance is the other current controlling factor. As per Ohm’s law, the higher resistance means lower current. In case of open, the infinite resistance means zero current, and zero resistance means infinite current.
From Ohm’s law, I = V/R.
Current for open → I = V/R = V/Infinite = 0
Current for short → I = V/R = V/0 = Infinite
The voltage across the short circuit is zero. However, the voltage across open circuit equals the supply voltage.
How it occurs
An open circuit occurs when a circuit is broken from some point, while a short occurs when some low resistance path occurs between two points.
- You are mounting the television plug into the wall outlet but one wire inside plug is not connected. That is open.
- The insulation of two wires in your extension breaks up. It is short.