Any disruption in the circuit, such as an open switch, a break in the wire, or a component, such as a resistor, whose resistance has changed to an excessively high value, may cause current to stop flowing. The open switch or the problem has resulted in what is known as a "open circuit."
An open circuit can be either temporary or permanent. A temporary open circuit is usually caused by damage to a part of the circuit, such as when water from a leaking pipe interrupts the electricity to a house wiring system. If this situation is not corrected, it could lead to more serious problems down the road, such as if a room is left dark when the power goes out.
A permanent open circuit is usually due to damage done while installing new wiring. For example, if a conductor is cut lengthwise with no replacement used, then there will be no electricity passing through that portion of the circuit, which would be visible as a broken wire. If this condition is not corrected, it could lead to other problems down the road, such as if a room is still powered after all the other wires have been connected up.
When checking circuits for open circuits, start with the most important ones first. Test the hot wire to each outlet you find, and then test the neutral wire where it enters the box. If neither check comes up closed, then there is probably nothing wrong with any of the other circuits.
An open circuit occurs when a faulty wire, circuit board trace, or solder joint "opens" the intended current channel. The flow of power then comes to a halt. Usually, nothing harmful happens; the circuit just does not work. However, an open circuit can also be used as a way for an attacker to gain access to otherwise secure equipment. For example, an open circuit condition on a network interface card (NIC) could allow an attacker to bypass security measures such as a firewall.
There is a break along the wire in an open or broken circuit, and the current ceases. Electric current can flow in a closed or full circuit. Electric current may be utilised by electrical items such as light bulbs while it flows. When electric current is interrupted, it also is interrupted from all of the connected equipment including any other circuits.
An open circuit can either be physical (such as when a wire is removed from a circuit) or functional (such as when a fuse has blown). A closed circuit continues to operate even after a connection has been made or a component has failed because another path through which current can flow has been provided. For example, if one side of a battery connects to ground then current will continue to flow through that path so long as the battery remains connected up. If two batteries are connected together then they replace one power source: if one goes out then the other can still provide power. In this case, the circuit is said to be closed.
In the case of electronic components such as transistors, diodes, and resistors, an open circuit means that there is no voltage across the terminals of the component; a closed circuit means that there is voltage across the component's terminals.
In terms of electricity, an open circuit means that there is no flow of current; a closed circuit means that current is flowing somewhere in the circuit.
One or more of the following can produce open circuits:
When a circuit is complete and current may flow, it is said to be in a closed circuit. The current has a complete route when the switch is closed. The circuit is "closed" and functional. Only when a switch is jammed in the "on" position will a closed circuit occur. If the switch is open, then the circuit is broken and no current can flow.
Closed circuits can be caused by any of the following:
1. A short circuit - where an electrical conductor such as a wire comes into contact with a ground or another conductor at some point inside the circuit. In this case, the entire circuit is "short-circuited", and all the voltage on the conductors goes straight into the ground or other conductor. This type of error can only happen with live power - not during testing or during downtime. It can happen if a conductor gets pinched between two parts of your wiring system or if a part of your wiring system comes into contact with earth ground. Check all your wiring for damage - especially after any heavy storms that could have brought down power lines.
Short circuits are usually very dangerous because all the voltage on the conductors goes right through you - whether you're working with live power or not. If you see smoke come out of one of your terminal strips, immediately shut off the power by turning off the main breaker.