The earth wire
A safety path for leaked current.
A leak in an appliance
A live wire inside an appliance with a metal body touches the body, so current leaks into the metal. The body is joined to the green earth wire, which goes into the earth.
Where does the leaked current go?
What this lesson covers
The idea
The earth wire (green insulation), joined to a metal plate deep in the earth, links an appliance's metallic body by a low-resistance path, so leaked current keeps the body at earth's potential and the user escapes a severe shock.
A leak in an appliance
A live wire inside an appliance with a metal body touches the body, so current leaks into the metal. The body is joined to the green earth wire, which goes into the earth.
Where does the leaked current go?
- Down the earth wire into the earth
- Into the person who touches the body
- Back along the live wire
Follow the leak
Press Next step to see the leak with no earth wire and then with the earth wire. This is a picture to read; home wiring is not for students to touch.
A low-resistance path
The earth wire has green insulation. It is joined to a metal plate deep in the earth near the house. The metal body of an appliance is joined to it. If current leaks to the body, it has an easy path, a low-resistance path, into the earth. That keeps the body at the potential of the earth. So the user may not get a severe electric shock.
The earth wire (green insulation), joined to a metal plate deep in the earth, links an appliance's metallic body by a low-resistance path, so leaked current keeps the body at earth's potential and the user escapes a severe shock.
Notes
The earth wire (green) joins the metal body of an appliance to the earth by a low-resistance path, so any leak keeps the body at the potential of the earth.
Check yourself
The earth wire has insulation of which colour?
The earth wire is usually connected to…
Why is the metallic body of an appliance connected to the earth wire?
A live wire leaks current to the metallic body of an appliance whose body is joined to the earth wire. The potential of the body…
- Red. Red is usually the colour of the insulation of the live wire.
- Black. Black is the colour of the insulation of the neutral wire.
- Green — correct. Yes!
- a metal plate deep in the earth near the house — correct. Yes!
- the electricity meter in the house. The meter is on the supply path. The earth wire goes to a metal plate deep in the earth.
- the main switch. The main switch connects the supply to the line wires. The earth wire goes to a metal plate deep in the earth.
- It makes the appliance work with a higher potential difference. The earth wire is a safety measure. It keeps the body at the potential of the earth.
- Leaked current gets a low-resistance path to the earth, so the user may not get a severe shock — correct. Yes!
- It raises the potential of the body above that of the earth. The earth wire keeps the potential of the body at that of the earth.
- rises well above that of the earth. The earth wire keeps the potential of the body at that of the earth.
- becomes the same as that of the live wire. The low-resistance path through the earth wire keeps the body at the potential of the earth.
- stays the same as that of the earth — correct. Yes!