and short circuits
can often cause more confusion and difficulty
in the analysis of a system than standard series or parallel configurations.
What is an open circuit?
An open circuit is two isolated terminals not connected by an element
of any kind, as shown in Fig. 1
. Since a path for conduction
does not exist, the current associated with an open circuit must always
be zero. The voltage across the open circuit, however, can be any value,
as determined by the system it is connected to.
In summary, therefore,
an open circuit can have a potential difference
(voltage) across its
terminals, but the current is always zero amperes.
Fig. 1: Defining an open circuit.
In Fig. 1(b)
, an open circuit exists between terminals a and b. The
voltage across the open-circuit terminals is the supply voltage, but the
current is zero due to the absence of a complete circuit.
Fig. 2: Example of an open circuit.
In a practical example provided in Fig. 2
, the excessive current demanded by the circuit caused a fuse to fail, creating an open circuit that reduced the
current to zero amperes. However, it is important to note that the full
applied voltage is now across the open circuit, so you must be careful
when changing the fuse. If there is a main breaker ahead of the fuse,
throw it first to remove the possibility of getting a shock. This situation
clearly reveals the benefit of circuit breakers: You can reset the breaker
without having to get near the hot wires.