Physics 31 - Dangers of electricity
LEARNING OBJECTIVES: 4.3 Electrical safety
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LEARNING OBJECTIVES: 4.3 Electrical safety
LEARNING OBJECTIVES: Electrical safety
What are four hazards of electric circuits?
Look at the picture and guess common hazards
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
http://ownersrepny.com/
In the UK, domestic electricity is supplied at a voltage of 230V (+/- 6%)
Mains electricity can be dangerous – possible hazards?
http://ownersrepny.com/
In the UK, domestic electricity is supplied at a voltage of 230V (+/- 6%)
Mains electricity can be dangerous – possible hazards?
Old, frayed wiring might mean strands of wire with a higher resistance at one point. A heating effect may be enough to melt the insulation and cause a fire.
http://ownersrepny.com/
In the UK, domestic electricity is supplied at a voltage of 230V (+/- 6%)
Mains electricity can be dangerous – possible hazards?
Old, frayed wiring might mean strands of wire with a higher resistance at one point. A heating effect may be enough to melt the insulation and cause a fire.
Extension leads may overheat if used when coiled up. The current flowing will warm the wire, but the tight bundle means that the heat has less room to escape.
http://ownersrepny.com/
In the UK, domestic electricity is supplied at a voltage of 230V (+/- 6%)
Mains electricity can be dangerous – possible hazards?
Old, frayed wiring might mean strands of wire with a higher resistance at one point. A heating effect may be enough to melt the insulation and cause a fire.
Extension leads may overheat if used when coiled up. The current flowing will warm the wire, but the tight bundle means that the heat has less room to escape.
If water leaks into a plug or socket there is a risk of someone getting electrocuted as water will conduct the current.
http://ownersrepny.com/
In the UK, domestic electricity is supplied at a voltage of 230V (+/- 6%)
Mains electricity can be dangerous – possible hazards?
Old, frayed wiring might mean strands of wire with a higher resistance at one point. A heating effect may be enough to melt the insulation and cause a fire.
Extension leads may overheat if used when coiled up. The current flowing will warm the wire, but the tight bundle means that the heat has less room to escape.
If water leaks into a plug or socket there is a risk of someone getting electrocuted as water will conduct the current.
When using a lawnmower of electric hedgetrimmer there is always the danger of cutting through the cable. A plug-in RCD(Residual current device) should always be used to avoid electrocution.
LEARNING OBJECTIVES: Electrical safety
Mains electricity
Mains electricity
Plastic insulated casing.
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Earth wire (yellow and green). Stops metal appliances becoming live if there is a fault.
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Earth wire (yellow and green). Stops metal appliances becoming live if there is a fault.
Live wire (brown) – goes alternately negative and positive, making current flow backwards and forwards through the circuit.
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Earth wire (yellow and green). Stops metal appliances becoming live if there is a fault.
Live wire (brown) – goes alternately negative and positive, making current flow backwards and forwards through the circuit.
Fuse – always connected to the live wire. If the current gets too high the fuse will ‘blow’ and break the circuit.
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Earth wire (yellow and green). Stops metal appliances becoming live if there is a fault.
Live wire (brown) – goes alternately negative and positive, making current flow backwards and forwards through the circuit.
Fuse – always connected to the live wire. If the current gets too high the fuse will ‘blow’ and break the circuit.
Cable grip – keeps the wires inside the plug securely.
Mains electricity
Plastic insulated casing.
Neutral wire (blue)
Earth wire (yellow and green). Stops metal appliances becoming live if there is a fault.
Live wire (brown) – goes alternately negative and positive, making current flow backwards and forwards through the circuit.
Fuse – always connected to the live wire. If the current gets too high the fuse will ‘blow’ and break the circuit.
Cable grip – keeps the wires inside the plug securely.
Plastic wire outer covering
Mains electricity
In some countries the plug may have only two pins (live and neutral). The earth connection is made by two metal contacts at the edge
Mains electricity
In some countries the plug may have only two pins (live and neutral). The earth connection is made by two metal contacts at the edge
Some appliances, for example radios, do not have an earth wire. This is because their outer case is made of plastic rather than metal.
The plastic acts as an extra layer of insulation around the wires.
Mains electricity
Mains current is 230V AC (in the UK). AC means alternating current. The current flows backwards and forwards 50 times per second. We say that it has a frequency of 50 hertz (50Hz).
Some appliances, for example radios, do not have an earth wire. This is because their outer case is made of plastic rather than metal.
The plastic acts as an extra layer of insulation around the wires.
Three pin plug-Live Neutral and Earth wire
SWITCH AND FUSE PLACEMENT
SWITCH AND FUSE PLACEMENT
Trip switch and fuses
Trip switch and fuses
Mains electricity
Fuses
Mains electricity
Fuses
How does the fuse and earth wire working together prevent shocks?
Mains electricity
Fuses
Mains electricity
Fuses
Mains electricity
Fuses
Mains electricity
Fuses
Mains electricity
Fuses
Mains electricity
Fuses
3A, 5A, 13A
Mains electricity
Fuses
3A, 5A, 13A
WARNING: if the wrong fuse is used then if a fault develops, the circuit might overheat and catch fire without the fuse blowing.
Mains electricity
Fuses
3A, 5A, 13A
WARNING: if the wrong fuse is used then if a fault develops, the circuit might overheat and catch fire without the fuse blowing.
To work out the fuse required we need to know the power rating of an appliance and the voltage rating. We can then work out the current used by the appliance using this equation:
I = P/V
Mains electricity
Fuses
3A, 5A, 13A
Eg. Hair dryer.
Power rating = 1.1kW
Voltage rating = 230V
Mains electricity
Fuses
3A, 5A, 13A
Eg. Hair dryer.
Power rating = 1.1kW
Voltage rating = 230V
I = P/V
I = 1100 / 230
I = 4.8A
Use the fuse rated a little higher than the normal current.
In this case, use a 5A fuse.
Mains electricity
Fuses
3A, 5A, 13A
Eg. Television.
Power rating = 150W
Voltage rating = 230V
Mains electricity
Fuses
3A, 5A, 13A
Eg. Television.
Power rating = 150W
Voltage rating = 230V
I = P/V
I = 150 / 230
I = 0.7A
Use the fuse rated a little higher than the normal current.
In this case, use a 3A fuse.
Mains electricity
Fuses
The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit. The fuse then has to be replaced.
Mains electricity
Fuses
The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit. The fuse then has to be replaced.
A circuit breaker does the same job as a fuse, but it works in a different way. Circuit breakers are automatic switches that ‘trip’ (turn off) when the current rises above a specific value. The circuit breaker can be reset by pressing a button (no need to replace).
http://wiki.diyfaq.org.uk/index.php?title=MCB
Fuses & trip switches
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
Double insulation
Earthing
Fuses & trip switches
LEARNING OBJECTIVES: Electrical safety
LEARNING OBJECTIVES: Electrical safety
