TYPES
OF FUSES:
There are just two styles of fuses: plug and cartridge. But, within
these two styles there are several variations.
Plug
Fuses-
This style of fuse has a screw base that screws into a socket in
the fuse box in the same way that a light bulb screws into a lamp
socket. There are three types of plug fuses: standard, type S, time
delay, and circuit breaker.
Standard
fuses-
They look similar to the bases of light bulbs. A metal strip runs
through the center at the top of the fuse. You can see it through
a tiny window. If the window looks black or discolored, the fuse
usually is defective.
Type
S fuses-
They are similar to standard fuses, except for one notable difference.
A type S fuse consists of two parts, the fuse itself and a socket
adapter. The adapter screws into and becomes part of the socket
in the fuse box. Do not remove the adapter unless it shows signs
of being defective, such as cracking or discoloration. The other
part, the fuse itself screws into the adapter. Threads of a particular
size (ampere) type S fuse are designed to be screwed into threads
of the same size adapter and no other. For example, a 15-amp type
S fuse fits only a 15-amp type S fuse adapter; a 20-amp type S fuse
cannot be substituted for a 15-amp type fuse. A type S fuse assembly,
therefore, prevents someone from replacing one size fuse with an
incorrect size, either by accident or on purpose.
Time
delay fuse-
They allow
temporary circuit overloading. In homes, time delay fuses are used
in circuits that accommodate heavy appliances, such as air conditions,
that cause a temporary surge in power when they are turned on. The
time delay fuse is made with a spring-loaded metal strip (link)
that attaches to a plug of solder. As the power surge takes place,
the fuse doesn't blow immediately, as would happen with a standard
type or type S fuse. Instead, the solder begins to melt. It must
melt through completely before the fuse will blow. The delay allows
for a limited period of power surge. However, if the overload continues
beyond a certain point, the solder melts completely and the spring
pulls the link free. The fuse then blows and interrupts the circuit.
Circuit-breaker
fuses-
These have a push button that pops out from the center of the face.
When the fuse blows, you simply push in on the push button to reset
the fuse. It works like a toggle-type circuit breaker.
Cartridge
Fuses-
Two types of cartridge fuses are used in homes. One type has round
ends and a capacity of 15 to 60 amperes. It is used to protect a
circuit on which there is a major electricity-drawing appliance,
such as a kitchen range, clothes dryer, or air conditioner. Each
circuit servicing a large appliance may be protected by a cartridge
fuse. The other type of cartridge fuse is used to protect the main
power circuits. This fuse has knife-blade contacts on each end and
is rated at a capacity of 60 to 600 amperes.
It is
rare for cartridge fuses to fail, but if there is no other explanation
for an inoperative appliance or for a power failure, it may be due
to the particular cartridge fuse. The main reasons for cartridge
fuse failure are the same as the reasons for plug fuse failure;
that is, overload on the circuit or a short circuit. A cartridge
fuse also may fail because of old age.
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