When subjected to extreme conditions, the fuse will blow or burn out.
Unlike a circuit breaker, a fuse cannot be reset.
It must be replaced.
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Fuse Boxes
A fuse box is a metal box containingscrew-in fusesand cartridge fuses.
Most older fuse boxes are rated at 60-amp total capacity.
By comparison, residential electrical systems today have a200-amp total capacity.
Fuses have an element that burns out, while circuit breakers have thermomagnetic switches that can be reset.
This puts fuses and circuit breakers in the same category, though they are different devices.
Any fuse must contain a fusible section: that is, a piece that is capable of being melted.
The fusible part is called the fusing element and is sealed inside the glass fuse body.
The fusing element is a thin strip of metal.
Thus, the circuit is broken, rendering the circuit dead and safe.
After a fuse blows, the fusing element is permanently broken, so the fuse cannot be reused.
It must be replaced with a fresh fuse.
Fuses for residential use will use two types: screw-in or cartridge.
How Fuses Blow
By design, fuses are the weakest link in the home’s electrical system.
All other wires and components in the electrical system are more robust than the fusing elements within fuses.
Why Fuses Blow
Overload Fuse Blows
A closed circuit works properly.
Blowing a fuse opens the circuit.
For example, turning on a microwave, hairdryer, and lights simultaneously may blow a fuse.
Electricity travels freely along copper wires and conductors.
Ground faults invariably will cause fuses to blow.
Or if the glass is clear, you might be able to see the severed fusing element inside.
Use a Testing equipment
Continuity testers and ohmmeters are inexpensive electronic devices that measure electrical resistance.
To check a cartridge fuse, hold the test leads at opposite ends of the fuse.
If the tester indicates a current, power flows through the fuse.
How to Change a Fuse
Your fuse box will have two sets of fuses.
At the bottom will be 15-amp and 20-amp screw-in fuses with glass faces that are exposed and visible.
These fuses will service branch light circuits and outlet circuits.
At the top will be 30-amp or 40-amp cartridge main fuses for ovens, laundry rooms, or stoves.
Cartridge fuses are hidden in fuse blocks that can be pulled out with handles.
Tools and Supplies You Will Need
Open Door
launch the door to the fuse box.
double-check you are standing on a dry floor and wearing rubber-soled shoes.
Find Blown Fuse
With a flashlight, look at the glass-front screw-in fuses.
If you find one thats burned or clouded, that is likely the blown fuse.
Unscrew Fuse
Unscrew the blown fuse by turning it counterclockwise.
As with unscrewing a lightbulb, do not touch the metal threaded section to avoid shock.
Add New Fuse
Screw the replacement fuse into place by turning it clockwise.
Again, avoid the metal threads on the fuse.
Locate Fuse Blocks
To replace a main fuse, first locate the fuse blocks.
Most 60-amp fuse boxes will have two fuse blocks, each with metal handles.
Remove Fuse Blocks
Grasp the metal handle or plastic T-shaped handle of the fuse block.
Firmly pull the fuse block straight out.
Set it on a table upside-down to expose the fuses on the back.
Replace Fuse Blocks
Slide the fuse blocks back into place in the fuse box.
Test the power by turning on a light or another gear on the circuit.
Every circuit requires about 20 amps, so multiply by the number of electrical outlets.
Most homes operating on a fuse box have a 60-amp total capacity.
However, most modern homes have many higher-load devices requiring more amps.
The average home operates on 100 to 200 amps.
If your electric load has exceeded 60 amps, you might consider upgrading to a circuit breaker.
bang out
There are two types of fuse boxesType-S and bang out-T.
The main difference between them is the base.
bang out-T fuses have Edison bases resembling a light bulb base.
These are typically found on older panels.
The different size bases prevent the wrong fuse from being used in the wrong fuse box.
For example, a 20-A fuse in a circuit rated 15-A may cause an overload.
Price
Fuse boxes are less costly to buy and replace blown bulbs.
Replacing a fuse box with a breaker box runs from $1,500 to $2,000.
If the wiring needs a complete overhaul, you might spend over $4,500.
Are Fuses and Fuse Boxes Code-Compliant?
Circuit breakers are standard, so all electricians are experienced at working with them.
Fuses and fuse boxes are not inherently hazardous.
But context can make them unsafe.
For one, fuse boxes are often attached to older knob-and-tube wiring systemsexposed wiring that usually should be replaced.
As a 60-amp service, fuse boxes cannot handle the increased energy demands of most contemporary homes.
Another issue with fuses is that some of the older fuse boxes lack rejection features.
It is possible to screw a 30-amp fuse in error into a hole meant for a 15-amp circuit.
Simple, fuse-based systems are unfamiliar to most do-it-yourselfers.
If you don’t feel confident replacing a fuse, consider contacting an electrician to complete that task.
Electrical Safety Hazards Handbook.
Los Alamos National Laboratory, U.S. Department of Energy.
What is a Short Circuit?
MIT School of Engineering.
How Much Does It Cost to Replace an Electrical Panel?Angi.
Circuit Breaker vs. Fuse Box: What’s the Difference?Angi.
National Electric Code, 2020.
Healthy Housing Reference Manual Chapter 11: Electricity.Centers for Disease Control and Prevention.
