Unit 2 - Mains Electricity Flashcards
Why does a fault occur in an electrical device?
The live wire comes loose and touches the metal case. This makes the casing live.
Which 2 wires are in a 2 core cable?
Live wire and neutral wire. There is no earth wire due to either the device being double insulated or the casing being entirely plastic.
Why do devices with plastic casing not need earth wires?
Plastic is in insulator.
State the frequency and voltage of UK mains electricity supply.
50Hz frequency and 230V potential difference.
What is a.c.?
Alternating current. Current that constantly changes direction. This is produced by power stations.
Give the colours of each of the wires in a 3 core plug.
Neutral blueLive brownEarth green and yellow
What type of fuse is needed in a plug for an oven, operating at 14A.10A, 14A or 18 A?
18A the fuse must have a rating higher then the operating current.
Describe what happens after a fault occurs in an electrical device.
Current flows from live to earth. This large current blows or melts the fuse. The circuit is broken and the metal casing of the device is no longer live.
Give 2 advantages of an RCCB over a fuse.
It can be resetIt is more sensitive than a fuse and therefore saferIt is faster to act (doesn’t let current build up)
Describe how an RCCB operates.
It detects a difference in current between the live and neutral wire. No more needed for Unit 2.
How is the wire in a 1A fuse different to that in a 5A fuse?
The wire is thicker in a 5 A fuse.
What is the risk of adding too many plugs to one plug socket?
Too large a current can be drawn which can cause the plastic coating the wires to melt/overheat and possibly cause a fire.
Why would a device be fitted with a 2 core cable?
It has either been double insulated or has a plastic casing.
