I don’t know much about how plugs or electricity works, obviously, but I was taught that one side is the “positive”, one side is the “negative”, and the bottom (seemingly quite optional) is the “ground”. It’s odd to me that so few plugs use the “ground”, so it made me curious why it exists, and why it’s optional. Are there any safety benefits to having a “ground”, or safety concerns with not having one? Thank you!
In: Engineering
AC power has two wires: the hot and neutral. The hot wire delivers energized current from the transformer to your appliance. When the energy is used up, it returns to the transformer at zero volts through the neutral wire.
All US plugs are polarized. Meaning you can’t accidentally plug the neutral side of an appliance into the hot side of the socket. If you look at a plug, the two prongs are different sizes. The skinnier one is the hot. Neutral is essentially the ground reference in AC circuits. So all devices are grounded for all intents and purposes, if they’re functioning normally.
Now, if you have a metal appliance, it’s possible that a fault inside may cause the hot wire to come into contact with the case. Causing the whole device to become energized. If you touch it, you become the path to ground. Thus giving you quite the shock.
The ground wire usually attaches to the chassis of metal appliances. It ties back to the neutral bus in your electrical panel. Electricity will always take the path of least resistance. The ground wire has a much lower resistance than your body, so the electricity will take that route. Now, since you’ve just essentially connected the hot and neutral buses together in your electrical panel, this creates a short circuit that will cause a huge spike in current. That sudden current spike will almost instantly cause the breaker to trip, cutting current flow to the appliance.
Ground prongs are typically only used on appliances that are both metal, and have exposed circuits inside that could potentially come into contact with the chassis. Things like metal lamps don’t have the latter. Plastic or ceramic are electrical insulators, so appliances made of those materials cannot become live.
Some electrical panels also have a second ground usually attached to a water pipe that goes underground. This is to protect the whole home from sudden power surges like lightning strikes. In this case, the Earth itself becomes the reference ground. But this isn’t the same ground as the ground prong on your plug.
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