EE Questions / AnswersEE-Tools, Instruments, Devices, Components & MeasurementsProtection

Why Earth Pin is Thicker and Longer in a 3-Pin Plug?

Why Earth Pin is Longer and Bigger in 3-Pin Plugs?

We know that electricity is our best friend as well as the worst enemy because if you give it a chance to kill you, remember, it will never disappoint you. Now you know that it’s all about safety and protection.

We also know that all the electrical appliances with metal bodies should be properly earthed and grounded. The reason behind this logic is that in any case, the Live (Line) wire touches the appliance metallic body, or in case of short or leakage current inside the appliance, and someone touch the metallic body of the machine, current will flow through the human body to the earth i.e. electric shock.

This is why proper earthing (grounding) is necessary to protect you and the person who touch the metallic body of the machine don’t get electrocuted.Why Earth Pin is Thicker and Longer in a 3-Pin Plug

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

  • The Green & 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 it is Longer?

The earth pin should be the first to connect and the last to disconnect with electric supply. This is why earth pin is longer than the live and neutral pin on 3-pin plugins. Below are the the reason to do so,

  • When we insert a 3-pin plugin into a 3-pin socket, the earth pin is the first to make a contact with the socket as compared to the Live and Neutral Pins.
  • The earth pin is the last to disconnect from the socket when removing the plug from the socket. i.e. Line and Neutral disconnect first and then the earth pin.

This way, earthing is well maintained during the operation for proper safety and protection. Now we know this is why the earth pin is longer as compared to Line and Neutral Pin on a three pin plug.

Why it is Thicker?

First reason, to prevent the wrong way to operate a 3-pin plug and connected electrical machine for the safety purpose. In other words, 3-Pin plug wont be connect 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.

Second reason for thicker pin is that the law of resistance.

R = ρ (L/a)   … [ Law’s of Resistance)


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

Related Post: Which Bulb Glows Brighter When Connected in Series and Parallel &  Why?

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 exist. Current will flow through it as it find 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.Why to Use 3-pin plugs and socket for electrical 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.

You may also read:

Show More

Electrical Technology


One Comment

  1. Dan Stark says:

    to distinguish it from the other pins and to engage the plug first to establish a grounded when plugging into the recepticle

Leave a Reply


Back to top button

Adblock Detected

Please consider supporting us by disabling your ad blocker