The current sent through our electric stoves and irons should be
strong enough to heat the coils, but not strong enough to melt them.
If the current sent through our electric light wires is too great for
the capacity of the wires, the heat developed will injure the wires
and may cause disastrous results. The overloading of wires is
responsible for many disastrous fires.
The danger of overloading may be eliminated by inserting in the
circuit a fuse or other safety device. A fuse is made by combining a
number of metals in such a way that the resulting substance has a low
melting point and a high electrical resistance. A fuse is inserted in
the circuit, and the instant the current increases beyond its normal
amount the fuse melts, breaks the circuit, and thus protects the
remaining part of the circuit from the danger of an overload. In this
way, a circuit designed to carry a certain current is protected from
the danger of an accidental overload. The noise made by the burning
out of a fuse in a trolley car frequently alarms passengers, but it is
really a sign that the system is in good working order and that there
is no danger of accident from too strong a current.
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