Unit D Lesson 3: Fuses and Circuit Breakers
Completion requirements
Unit D Lesson 3: Fuses and Circuit Breakers
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Learning Targets |
Big Question: How do
fuses
and
circuit breakers
prevent fires?
Electricity will flow as quickly as it can along the easiest route it can find. We have learned to use devices like fuses and circuit breakers to help protect us from electricity moving in ways that are dangerous to us and our structures.
Electricity will flow as quickly as it can along the easiest route it can find. We have learned to use devices like fuses and circuit breakers to help protect us from electricity moving in ways that are dangerous to us and our structures.
At the end of this inquiry, you should be able to answer the following questions:
- What is a short circuit?
- How do fuses and circuit breakers work?
- What steps can be taken to protect you from an electrical shock?
Pages 284 to 287 in your textbook will help you answer these questions about fuses and circuit breakers.
Introduction
Figure 1– Electrical safety is important for everyone, including monsters.
What is each character in Figure 1 doing that is electrically unsafe?
The seven characters in the haunted house are taking part in unsafe electrical practices. What are they doing that is not safe?
Check your answers by clicking on the “Check your answer” button.
The seven characters in the haunted house are taking part in unsafe electrical practices. What are they doing that is not safe?
Check your answers by clicking on the “Check your answer” button.
- Dracula is using a hair dryer beside water; water and electrical devices can cause severe damage.
- The Hunchback is flying his kite near a power line; the kite could contact the power line and cause him to be electrocuted.
- The woman is trying to take her toast out of her toaster with a metal object; this could electrocute her.
- The man is sticking a metal object into an electrical socket; he can be electrocuted.
- The Mummy has clothing close to a lamp; lamps get very hot and this could start a fire.
- Frankenstein is holding a toy by its cord; the cord could become damaged and then cause an electric shock when it is plugged in.
- The werewolf has a trunk sitting on a cord, which could damage the cord; an electric discharge could occur when it is plugged in. This could lead to a fire.
Background Information
Realize that electricity can be very dangerous if safety rules and knowledge of electricity are not understood. The danger of electric shock has more to do with the current rating than the voltage rating. When electricity flows
at rates of more than 0.02 Amps, it can cause a severe shock. Only 0.1 Amps of electricity can be fatal – and your electric kettle might use 12 Amps!
Electricity is lazy and always takes the shortest path. Electric shocks can occur when electricity has a short circuit . In Lesson D1 you learned that lightning tries to take the shortest path to the ground, and therefore, you should not stand under a tall tree or be in any high places especially with metal objects during thunderstorms.
Figures 2 and 3 both show examples of potential short circuits. What you should do in each situation? Why should you do that to avoid a short circuit through your body? Click the hint button for correct answers to appear.
Electricity is lazy and always takes the shortest path. Electric shocks can occur when electricity has a short circuit . In Lesson D1 you learned that lightning tries to take the shortest path to the ground, and therefore, you should not stand under a tall tree or be in any high places especially with metal objects during thunderstorms.
Figures 2 and 3 both show examples of potential short circuits. What you should do in each situation? Why should you do that to avoid a short circuit through your body? Click the hint button for correct answers to appear.
Figure 2
– Car accident, with downed power lines on car.
What should you do in this situation? Why? What do you know about electricity and the ground?
Stay in the car or
jump
out of the car (without touching the metal of the car or the wires. If you place one foot to the ground, the electricity will have a short path to the ground and run directly though you. This is a short circuit.
Figure 3 – Golfing in a thunderstorm.
What should you do in this situation? Why? What do you know about lightning and the tallest object on the ground?
The metal club is a good conductor and provides a shorter path for the electricity to get to the ground.
Do not golf in the rain
to avoid becoming a short circuit for lightning. Lightning loves the shortest path to the ground and is attracted to objects that are good conductors such as golf clubs.
Try It!
Practice Worksheet: Electric Safety
- DOWNLOAD this practice worksheet (S9_UD_S1_L3_electric_safety) worksheet. If you prefer to use a Google Drive or PDF version of the worksheet, click here.
-
Check out what a duck knows about electrical safety and how you can save yourself from a major disaster by watching the three videos below
"Dexter Duck", "Electrical Safety at Home", and "Electrical Safety Tips".
Use the worksheet to make a list of the safety precautions you observe in the videos. If you want additional ideas on safety precautions, please see page 285 in your textbook.
- When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below the videos.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
Watch the video "Dexter Duck: Electrical Safety Video".
Watch the video "Electrical Safety at Home".
Watch the video "Electrical Safety Tips".
- Do not have electrical devices beside water.
- Do not overload plug-ins.
- Watch for frayed and worn or damaged cords.
- Avoid cords lying on the ground.
- Do not touch power lines and avoid fallen power lines.
- Avoid being outside in thunderstorms.
- Only electrical plugs can go into power outlets.
- Remove cords from outlets safely. (Pull the plug and not the cord!)
- Do not run cords under rugs because the cord could overheat.
- Use extension cords outside only if they indicate they are for outside use.
- Grab a plug by the head of the plug at all times.
- Use GFCI protection outlets, especially in areas that may be subject to moisture.
- Turn off circuit breaker if outlets are hot to touch.
- Cover outlets when small children are present.
- Be sure to label each circuit breaker in the panel box.
- Be educated about circuit breakers.
- Use surge protectors
- Unplug your electronic devices during thunderstorms.
Preventing Electric Shocks
Conductors allow electrons to flow through them. Understand that some materials do not allow electrons to flow through them and they are called insulators. When many electrons flow through some material, a higher amount of electricity is available than if fewer electrons flow through some material.
Insulators are important when dealing with electrical safety. Insulating material is placed around household wires to direct the electricity to the location where it will be used and to prevent you from being shocked.
Conductors allow electrons to flow through them. Understand that some materials do not allow electrons to flow through them and they are called insulators. When many electrons flow through some material, a higher amount of electricity is available than if fewer electrons flow through some material.
Insulators are important when dealing with electrical safety. Insulating material is placed around household wires to direct the electricity to the location where it will be used and to prevent you from being shocked.
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Rubber, wood, and plastic are effective insulators.
- Copper and other metals are effective conductors.
Figure 4 – A circuit breaker box has many switches.
Preventing Household Electrical Fires
Two devices found in homes commonly used to prevent electrical fires are circuit breakers and fuses. Both are put into circuits to help prevent current overload - which could result in a house fire!
A fuse is a small piece of wire inserted into a circuit that melts faster than the other conductive wire being used. When the circuit has too much current passing through it, the wire inside the fuse breaks and stop the flow of electricity.
Two devices found in homes commonly used to prevent electrical fires are circuit breakers and fuses. Both are put into circuits to help prevent current overload - which could result in a house fire!
A fuse is a small piece of wire inserted into a circuit that melts faster than the other conductive wire being used. When the circuit has too much current passing through it, the wire inside the fuse breaks and stop the flow of electricity.
A circuit breaker is similar to a fuse but it is reusable and does not require replacement each time the current is above the maximum value. If a circuit breaker becomes too hot, the metal expands and pushes a switch to turn off the circuit.
Always give the breaker time to cool and be sure to reduce the load on the circuit before you reset the circuit breaker.
Circuit breakers are located in panel boxes, which are often in household basements. Do you know where the panel box is in your house? Have you ever reset a breaker? (Look for it so you can identify it and ask some questions about how it works!)
Circuit breakers are located in panel boxes, which are often in household basements. Do you know where the panel box is in your house? Have you ever reset a breaker? (Look for it so you can identify it and ask some questions about how it works!)
Figure 5 – A fuse is a safety device that is designed to fail.
Watch
When is a circuit breaker more useful than a fuse? To find out, watch
"What is the Difference between a Circuit Breaker and Fuse?"
Ever wonder what is inside the circuit breaker panel? Watch the video "Circuit Breaker Dis-assembly and How it Works" to discover the inside of a breaker switch
There are many types of circuit breakers, but what makes them work? To see the inside of a circuit breaker and how many forms of circuit breakers are available, watch "What is a Circuit Breaker?".
Watch
Fire safety in the home is very important. Different types of fires must be handled in different ways. Watch "Home Safety Tips : How to Put Out an Electrical Fire" to learn about fires involving electricity.
Lightning Rods
Have you ever thought about how we can protect our homes from being hit by lightning? There is no way to stop lighting from striking, but using a lightning rod is a way to redirect all of that energy away from our structures and to the ground without any severe damage occurring.
Lightning rods are a common occurrence in homes throughout the country. These metal rods stand above the roof of the house and connect all the way into the ground. This way, if lightning were to hit the house, it would contact the lightning rod first because it is the shortest path to the ground. This is a simple way to protect all electrical devices from being short-circuited by a lightning strike. All electrical wiring, all plumbing, and all gas lines are grounded – that is, they are connected to metal that is underground near your house.
Have you ever thought about how we can protect our homes from being hit by lightning? There is no way to stop lighting from striking, but using a lightning rod is a way to redirect all of that energy away from our structures and to the ground without any severe damage occurring.
Lightning rods are a common occurrence in homes throughout the country. These metal rods stand above the roof of the house and connect all the way into the ground. This way, if lightning were to hit the house, it would contact the lightning rod first because it is the shortest path to the ground. This is a simple way to protect all electrical devices from being short-circuited by a lightning strike. All electrical wiring, all plumbing, and all gas lines are grounded – that is, they are connected to metal that is underground near your house.
Watch
How do lightning rods protect us? Find out by watching
"Lightning Rods".
How much money will lightning rods save you if your house is hit by lightning? To see why lightning rods might be worth your investment, watch the video "Lightning Rods Can Protect Home from Damaging Strikes".
What are lightning rods made of? To find out, watch the video "Lightning Conductor".