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FUSE
SIZES:
As already noted, all fuses are rated in amperes. They will be stamped
with numbers or ratings from 15 to 60 or 60 to 600 amps. As a rule
of thumb, a No. 14 wire (regular lamp circuit) takes a 15-amp fuse
(1750-watt capacity); a No. 12 wire circuit takes a 20-amp fuse
(2300-watt capacity); a No. 10 wire takes a 30-amp fuse (3500-watt
capacity). The chart at right gives the recommended (minimum) fuse
amperage size for typical household circuits.
WARNING:
Do not change fuse size in a circuit. If your system has been plagued
by burned fuses because of overloaded circuits, do not solve the
problem by substituting a larger fuse for a smaller one. Such action
seriously jeopardizes the safety of your home. The wire in a 15-amp
circuit has more resistance than wire in a 20-amp circuit. When
a wire resists current, energy is dissipated in the form of heat,
which in turn can cause a fire. The resistance level of the metal
strip in a fuse should match the resistance level of its wire. Normally
the wire and the fuse strip don't heat up because they carry no
more current than they can handle. If, however, you replace a 15-amp
fuse with a 20-amp fuse, your system is in trouble. Once the current
goes over 15 amps, the wire begins to heat. However, the 20-amp
fuse, which responds only to an amperage level of over 20 amps,
does not respond at all. Because of the difference between the fuse
and the wire sizes, there is too much current in the circuit and
you have created the potential for an electrical fire.
It is
wise to keep spare fuses handy near the fuse box.
Troubleshooting
a Circuit:
When a fuse blows and the power goes off, the most likely cause
is usually an overloaded circuit. An overloaded circuit is when
too many appliances or lights are plugged into a circuit. When overload
occurs, the small wire in the fuse breaks without heating excessively.
The window on the fuse should be clean so you can see the broken
wire.
Fuses
that continually blow usually can be traced to an overloaded circuit.
So, before you replace a blown fuse, check along the circuit for
the overload: too many lights? too many appliances? Correct this
situation and replace the fuse.
The second
cause of fuse problems is a short circuit, which is one bare electrical
wire touching another bare wire or piece of metal. The rate of f
low of the electric current is excessive when a short circuit occurs.
The fuse wire vaporizes, spraying and discoloring the fuse window.
To
check for a short circuit-
- Turn
off the power (main fuse) at the service panel.
- Unplug
all lamps, overhead fixture light bulbs, and any appliances on
the failed circuit.
- Check
the wire plugs. If a plug is cracked, has melted from heat, or
has broken prongs, do not reconnect the plug until it has been
either repaired or replaced. Replacements are cheap.
- If
you spot a worn or frayed wire on a lamp or appliance cord, replace
or repair it.
- Replace
the fuse on the circuit with ALL appliances, lamps and other electrical
devices disconnected.
- Wait
one minute. If the fuse blows again, the problem is the house
wiring - usually behind a wall. Call a professional electrician,
unless you can spot and repair the damage.
- If
the new fuse doesn't blow, the wiring is okay.
- Remove
the fuse.
- Reconnect
one of the disconnected items. Replace the fuse. If the fuse doesn't
blow, this lamp or appliance is not the problem. Continue plugging
in all items on the circuit.
- Always
remove the fuse and plug in the device. Then replace the fuse.
The device with the short circuit will blow the fuse. Repair device
before you replace the fuse.
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