Troubleshooting Faulty Fuses

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-

1. Turn off the power (main fuse) at the service panel.
2. Unplug all lamps, overhead fixture light bulbs, and any appliances on the failed circuit.
3. 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.
4. If you spot a worn or frayed wire on a lamp or appliance cord, replace or repair it.
5. Replace the fuse on the circuit with ALL appliances, lamps and other electrical devices disconnected.
6. 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.
7. If the new fuse doesn't blow, the wiring is okay.
8. Remove the fuse.
9. 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.
10. 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.

REPLACING BLOWN PLUG FUSES:
The first step is to turn off all lights and appliances on the circuit controlled by the fuse. Then turn off the main power. In newer houses, the main power is controlled by two boxes that are equipped with cartridge fuses. To shut off the main power so you can safely remove the blown fuse, grasp the handles of the cartridge boxes, one at a time, and pull the boxes from place. In older houses, the main power is controlled by a lever type switch on the side of the fuse box. To cut the power, pull this switch downward.

Actual fuse replacement is simple, but use care when working at the panel.

1. Select a fuse rated for the same amperage as the one you are replacing.
2. Turn the blown fuse counterclockwise to remove it from the fuse box.
3. Install the new fuse by screwing clockwise into the socket.
4. Replace the main fuse boxes or turn the main power on.

REPLACING FAULTY CARTRIDGE FUSES:
To determine if a cartridge fuse has failed, proceed as follows:

1. Turn off the main power and open the service panel of the fuse box.
2. Using a fuse puller, grasp the middle of the fuse and pull it out of the spring clips that hold it in place. If the fuse has knife blade ends, don't bend them.
3. Some cartridge fuses are mounted in a compartment-type housing. To remove the fuses, grasp the wire-loop handle and pull the compartment straight out of the panel.
4. To test the fuse, touch one probe of a continuity tester to one end of the fuse and the other probe to the other end. If the tester lights, the fuse is okay. If the tester does not light, replace the fuse. CAUTION: Never test a fuse while it is in the service panel. Always remove it from the service panel.
5. To install a cartridge fuse, push it into the spring clips by hand. If a new fuse fails, the problem is in the circuit wring or there is a short circuit in an appliance.