Electrical Safety Flashcards
What is an alternating current and when do we get it?
-a current that only flows in one direction so keeps changing directions.
-we get it when we use an alternating potential difference.
Where is alternating current used and how much Hz and V does this have?
-in UKs mains supply.
-it has 50Hz and 240V.
What is direct current and when do we get it?
-a current which charge always flows in the same direction.
-produced by a direct potential difference which is either positive or negative.
Where is direct current used?
-used in cells/batteries.
What is an oscilloscope?
- a device used to display how voltage changes over time.
-they display these graphs on a monitor.
How are the wires in three-core cables protective?
-they have the copper which conducts electricity and they are coated in a layer of insulated plastic for safety.
What are the names and colours of each of the cables?
-live wire: brown
-neutral wire: blue
-earth wire: green and yellow striped
What are the functions of each of the three cables?
-live(brown): provides alternating potential difference of 230V from the mains supply.
-neutral (blue): acts to complete the circuit by carrying away current.
-current basically flows in through the live wire and out through the neutral wire.
-earth wire doesn’t normally carry a current, stops the appliance casing from becoming live if live wire became loose and touched the casing.
-it provides an alternative pathway for the current to flow away as live wires can cause electric shocks so current goes through earth wire rather than us.
Why is the electricity from the live wire able to pass through the earth and neutral wire and why could this be a problem?
-both the earth and neutral wire have a potential difference of 0V and live wire has 230V.
-it is this difference in voltage that causes electricity to pass from one to the other.
-the problem is humans are also 0V so touching the live wire can give us an electric shock so its important to not touch plug sockets even when turned off.
What is the main thing that can go wrong with electricity?
-sudden increases in current cuasing surges.
-this can happen when you turn an appliance on or off or when there is a fault in the circuit/appliance.
-this can cause fires or electric shocks.
What do fuses and circuit breakers do?
-break the circuit whenever the current gets too high.
How do fuses work?
-a very thin piece of wire connected to the live wire.
-the surge will flow through the live wire and therefore flow through the fuse.
-this causes the very thing wire to heat up and melt breaking the circuit.
How do you know which current you need to break the circuit?
-get a fuse that is a few amps higher than the current you need to break the circuit.
-for example, if your appliance has 3A, you will get an 5A rating.
What is an advantage and disadvantage of fuses?
-they are simple and cheap.
-they are permenatly broken after a single use.
How do circuit breakers work as
and what is a downside?
-they break the circuit whenever there is a surge (like fuse).
-however, they are not permenantly damaged, they are just tripped and turn of the circuit.
-a downside is that they are more expensive than fuses.
