Electrical fires can be deadly. They happen quickly, often without warning, and spread inside walls. Electrical fuses and circuit breakers are your first line of defense against this type of danger.
Here, we explain “how do fuses and circuit breakers protect your home?” and how to reset a fuse or breaker once it’s tripped.
Background: How power works in your home
First, let’s give a brief overview of how electricity gets to your house:
- Electricity is created, or made, at large stations. These stations use wind, natural gas, coal, or water to create power within generators.
- Electricity travels as a current, or charge. Transformers amplify and push the currents from the power stations to a power grid. Grids can be made up of power stations, substations transformers, and power lines that deliver high-voltage electricity.
- Small transformers in or near your neighborhood reduce the power flow to a safe level for home use. Some are mounted to poles, and some sit on the ground as large green boxes.
- Power lines go from the pole box to your house, or underground from the pad box to your house.
- A meter is mounted to the outside of your home. The meter measures how much power your house uses. It connects the intake wires to your service panel, which then delivers power to the rest of your home.
- Within your home, electricity moves in a series of circuits. When a circuit opens or closes, power is delivered to your appliances, such as your fridge or a lightbulb.
Check out this cool video where “This Old House” electrician Scott Caron shows how fuses and circuit breakers work to keep you safe!
How do fuses and circuit breakers work?
Circuit breakers or fuses are inside your service panel. They help to measure and control the voltage, current, and resistance of electrical charges.
- Voltage is the amount of pressure an electrical charge makes as it moves to power your appliance.
- Current is the rate of flow of the charge.
- Resistance is the tampering of the flow. The amount of resistance each appliance creates varies, and the total amount of resistance in your home is described as the load.
Each of these pieces works together to ensure that there isn’t too little or too much charge in one area. Too much flow could cause the wiring to overheat, which is how fires are caused.
Your circuit breaker measures the levels of electrical current running through your home. If the current’s flow is too high or too low, it will either blow a fuse or trip a circuit, cutting off the power.
What is a fuse?
A fuse is a small, simple device that protects your home’s overall circuit.
A fuse is composed of a small, thin wire or filament in a casing. The casings can be metal, ceramic, or glass.
The electrical flow passes through the fuse without any barrier. If there is too much load on the circuit, however, the fuse will melt.
When a fuse melts, it burns the filament. Anything that was powered from that circuit is now off.
The downside of fuses is that they are only able to activate once. Once the filament is burnt, it must be replaced.
What is a circuit breaker?
A circuit breaker works exactly like a fuse, except that it is reusable.
A circuit breaker is, in essence, a switch connected to a magnet or bimetallic strip.
If the current rises above a level that has been set, the magnet pulls down a lever attached to the switch. If a switch is tripped, the power is disconnected. However, once the switch is tripped, it can be reset, and power will be restored immediately.
Usually, smaller circuit breakers are available to protect individual appliances and areas. Think of GFCI (Ground Fault Circuit Interrupter) plugs that are located in your bathroom or kitchen.
These small breakers are usually connected to bigger ones on or near your power supply.
What is the purpose of fuses and circuit breakers?
The main purpose of fuses and circuit breakers is to control the flow of electricity going into and through your home.
Breaker box vs fuse box: The main differences
Both circuit breakers and fuse boxes protect your home from an overload or worse, an electrical fire.
A fuse box is made up of many smaller fuses, usually arranged in a circle. Each of the smaller fuses protects an appliance or area of the home, and they are more sensitive to current changes. In a fuse box, the individual fuses can be replaced, and if one is burnt, you just replace the individual fuse. They are relatively cheap, and most home improvement stores and hardware stores sell them.
A breaker box has the same function, except instead of a piece that must be replaced, there is a switch that has to be flipped. These can be reused over and over, but are not as sensitive to current changes.
If a circuit breaker trips, the switch will go from pointing to the “on” position to pointing to the “off” position.
What do the numbers on a circuit breaker mean? What about fuses?
The electrical panel has individual circuit breakers, usually aligned from top to bottom.
Usually, at the top, there is always one circuit breaker in the box that is bigger than the others. This is the main power line and will shut off the power to everything.
The numbers in a circuit breaker box are the same as the number of amps that the circuit will allow before it trips. You will see either 120 or 240 – this is the number of volts it can take. The amps will also be listed either individually by a switch, or above a column of switches.
Other circuit breaker markings could include overcurrent rating and other current flow measurements.
The numbers in a fuse box show how many amps each fuse will allow for a circuit. Each fuse may have a different rating. When replacing fuses, make sure you replace one with the same voltage and amp metering.
Some boxes will also have numbers on the very outside of the switches or fuses that correspond to a list on the inside of the box. The list details which breaker powers what appliance or area.
How to find a tripped breaker in a breaker box
When a fuse trips, it’s easy to see – it will be burnt. However, circuit breakers are slightly more difficult.
Each circuit breaker switch can be reset within the main box of your home.
How to reset a tripped circuit breaker
- Locate your main breaker box
- Identify which switch is in the OFF position.
- Turn off any appliance or unplug anything that is drawing power from that circuit.
- Flip the switch back to the ON side.
How do auto-reset circuit breakers work?
Auto-reset circuit breakers work by cycling the power, keeping electricity flowing. These protect your home during overcurrent flows.
How to tell if a fuse is blown
Fuses will break down over time, so it is important to distinguish between a blown fuse or one that has failed.
A fuse is usually in a glass tube. If the wire inside is disconnected, or you see a dark smudge similar to a blown light bulb, then that fuse needs to be replaced.
Check your fuses on a semi-annual basis to ensure they are operating properly.
How to replace a blown fuse
- Inspect the fuse box for a blown or damaged fuse.
- Unplug or disconnect all appliances from that circuit.
- Remove the fuse from its box.
- The fuse will have markings on it that show its amp and voltage ratings, as well as its specific type. Replace the blown fuse with a new fuse exactly similar to the blown fuse.
Fuses are relatively cheap – it is wise to keep some in stock in your home in the event one is blown.
Common reasons circuit breakers and fuses blow
- Too many appliances are plugged into one circuit.
- Too many LED or high-powered lights are drawing from one circuit.
- One outlet or appliance is sapping too much power from one circuit.
- A short has developed in a circuit.
- A ground fault, such as a grounding wire, occurs within the current flow.
- A terminal has a fault, causing an arc.
- The circuit breaker itself has damage, or has loose connections.
- An incorrect switch or fuse was installed in the power box.
- Outdated or faulty wiring causes a power surge.
- The wiring is damaged. This can happen during DIY projects; replacing outlets, lights, or fixtures; or even something as simple as hanging a picture, and the nail punctures the wire.