Question: Why in a three pin plug earth pin is thicker and longer than other two pins?
Ans: Resistance, R=pL/A
Where, A is inversely proportional to R, so if A increases R decreases, so leakage current will easily take low resistance path. (This is the reason to make earth pin thicker)
For safety purpose it is made longer because the first to make connection and last to disconnect should be earth pin.it assures safety for the person who uses that equipment.
