http://amasci.com/amateur/whygnd.html
This is now the third time I've posted this article on this blog. However, the most recent time was over 16 years ago, so consider this post the sweet 16 celebration for the prior post.
Every few years I think of this article, and want to read it, and it always takes me a while to find it. It really is a good overview of what the various components of the electrical system do.
QUESTION:
WITH AC POWER, AREN'T BOTH WIRES OF THE PAIR INTERCHANGABLE? Why is one wire called "neutral?" What's all this stuff about "grounding?"
Why are three prongs needed?
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ANSWER:
Yes, in an Alternating Current system there is no "plus" and "minus," so in theory the two wires should be interchangable. However, the real world is a bit more complex than the theory. Other issues crop up and cause trouble.
If you were to build your own electric power distribution system, you'd quickly discover some unexpected and strange effects. Sometimes your customers' appliances would fail for no apparent reason. And sometimes when you reached for a light switch, a foot-long spark would leap out to your hand and knock you senseless! What the heck?! It takes a huge DC voltage to make a foot-long spark. Why are high DC voltages appearing on your AC power lines?
