In Our home appliances, we are having some are two pin-plugs and some are three-pin plugs. If you see in any place around the world, you will find the same concept behind every three pin-plug. A top pinhole of a socket and top pin of three-pin plug is bigger as well as thicker than the rest of the two pins(Live and Neutral pins).

In a 3-pin plug ( as shown in the above fig)

• The Green  and Yellow Wire is Earth (IEC & NEC)
• Brown is Live / Line (Black in US)
• Blue is Neutral (White in US)

Now to the points, why the earth pin is bigger and thicker?

WHY Earth pin is Bigger?

Earth pin is bigger(longer) than live and neutral pins. When the plug is inserted in the socket, cause of longer earth pin first it makes contact to the earth hole prior to live and neutral. Thus earth connection is made before the current-carrying contacts of the plug become live. When the plug is removing from the socket, Earth pin comes out last. Means earth connection is removed after the current-carrying contacts separate. Due to this, it can protect us from any kind of shocks.

WHY Earth pin is thicker(Area of cross-section)?

First reason, to prevent the wrong way to operate a 3-pin plug and connected electrical machine for the safety purpose. In other words, the 3-Pin plug won’t be connected to the socket upside down as the earth pin is thicker, so it won’t adjust and fit in another slot made for Neutral or Live Pin in the socket. In short, The earth pin is bigger and it can not be inserted in the live or neutral slot of the socket even by mistake.

The second reason for the thicker pin is that the law of resistance.

Where:

• R = Resistance
• ρ = Resistivity
• L = Length of the Conductor
• a = Area of the conductor

It clearly shows that the resistance is inversely proportional to the area of the conductor. i.e. thicker of the conductor, lesser is the resistance. In this case, when a wet body (Keep in mind that wet body has very low resistance) touches the metallic body of the machine where leakage current exists. Current will flow through it as it finds the easiest way (having very low resistance) to complete the path. So there is still a chance of electric shock in the above-mentioned case.

Third reason, modern 3 pin wall sockets have safety shutter (as shown in below fig) on the Line and Neural lines to prevent someone (especially children) to insert conducting materials in it which cause electric shock. In this case, the longer earth pin help to open the shutters for Line and Neutral pins i.e. without longer earth pin, The shutters for Line and Neutral remains closed for better safety.

Now we know another reason that’s is why the earth pin on a 3-pin plug is bigger other than Neutral and Live pins.