Why earth pin is thicker and longer?

Most of the plug and sockets are 3 pin type which consists of a phase, neutral and earth. In a 3 pin plug, the earth pin is thicker and longer in size compared to the other two pins. Did you ever think why it is? There are some practical reasons for that.

Connect first, disconnect last

The longest pin of the plug comes first in contact and comes out last.

So while plugging, the length of the earth pin makes the plug contact first with the earth line. And during unplugging the phase can disconnect before the earth connection is separated from the plug. Thus, the device always maintains a connection with the earth before the phase line of socket touches the current carrying contacts of the plug and disconnects the earth only after the phase disconnection. So even the supply to the socket is ON while plugging a complete earthing can be ensured.

 Avoid wrong plug-in

It helps to prevent the wrong plug-in of three pin plug in the socket. So the plug and socket connection will have an exact proper contact (Earth pin cannot be inserted into the phase or neutral points).

Some new electrical sockets have a safety shutter (Earth-pin operated shutters) which can open only by plug-in earth pin of the plug. Thus it ensures that the socket is connected only by its right alignment.

For Low resistance

If the earth has a higher resistance than other contacted points such as a human body (suppose a wet human body; a wet human body will have much lower electrical resistance), then the current will definitely flow through the body. Because the current flows more easily through the least resistive path.

So an earth connection should have electrically low resistance compared to the remaining conductive paths. So in case if there is any fault with the appliance, the fault current or leakage current will easily flow through the earth wire.

The resistance R of a conductor is inversely proportional to its cross-sectional area. Hence a thicker earth pin increases its cross-sectional area, which makes the earth pin low resistive. And makes an easy path for the charge flow.

Also, the wire connected to this earth pin must be of low resistance to make a complete low resistive conductive path.

The size of the earth pin makes no considerable change in resistance compared to the dimension of the other two pins. But this can be also considered as a reason.