Sunday, July 6, 2008

32 Bit Thinking... # 2

Why the top most pin, biggest in a plug point??


Guys from my point of view, there are two major reasons that accounts for the answer....

-> When we turn on the switch., a large amount of current starts to flow.. So it becomes highly necessary for us to ground it immediately. The top most pin(also called earth hole) serves this purpose.

-> The reason why it is big - The property of the current is that it takes low resistance path. As the resistance is inversely proportional to the area of cross section(from the formula: R = P*l/A), the earth hole's bigger size serves as the low resistance path for the large initial current flow.

More relevant answers to the question are welcome in the comments section.
Best regards.

2 comments:

gangadharan said...

Assuming that bigger pin = longest pin, the answer is a bit different:

We don't want anyone to be able to plug the appliance in without earthing it. So at anytime the + and - are in, the earth defenitely has to be in.

http://wiki.answers.com/Q/Why_earth_pin_is_longer_in_3_pin_plugs

balaji said...

It is big/long because, when we take out the plug from socket the phase & neutral terminals of socket comes first, then the earth contact. This is primarily for the safety purpose. Earth contact disconnects at the last to support abnormal conditions.