eli5: Whats the purpose for the ground wire?

Question

I understand if we touch the wire and were are on the ground it creates a complete circuit. So we get electrocuted.

But how does the ground or earth wire works, so that we don’t get electrocuted?

In: Engineering

Answer 1

Electricity is really weird stuff. It likes to flow through some things better than it flows through other things.

An example is a nine-volt battery with the two little knots on the top. Electricity doesn’t like air very much – it’s an “insulator”. But it LOVES many metals and it loves salty water. So if you lick that battery, the salt water on your tongue gives the electricity in the battery a little highway that it likes much better than air, so it jumps on and you get a shock.

And some things are way way better than others. A wire? Ooh, it hops RIGHT on board. But a human body? Well, you need a lot of electricity to overcome the resistance (level of insulation) before it’ll go through your body. This is why your dry finger on that battery’s top won’t give you a shock, but putting a fork in an electrical outlet can electrocute you. (Note: please don’t try this.)

So you hook up a ground wire to give the electricity a very convenient path to go along instead of through your body and what you’re touching. So if you’re a technician that’s working on a computer circuit board on a dry day where there’s carpet, you hook up a “ground wire” to connect yourself to a metal table, which has way less resistance than the path through the motherboard and tools you’re using. Instead of a big static charge snapping through that board, like what happens when you scuff your sock feet and then touch a doorknob, the electricity follows the convenient low-resistance wire, and you don’t damage your electronics when you take a screwdriver to them.

Ground wires in three-prong electrical cords are the same. In the event something goes wrong in a household appliance that’s powered by electricity, the ground wire provides a way for the electricity to exit INSTEAD of your own body because that wire has lower resistance.

Same thing for “lightning rods” on buildings – they provide a connection to the ground that is not the building itself, and a strike flows through the conducting wire rather than setting fire to the more resistant building.