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
In the two-prong plugs, one is hot and the other is ground. In the three-prong plugs, one is hot and two are ground.
In the event of a failure on the wire, before the outlet, the extra ground can save lives and prevent fires. This usually means a break in the wire.
If the hot wire fails, generally there’s no problem, as electricity won’t flow to or through the outlet, stopping where the hot wire has failed. Any thing connected to that outlet turns off.
If the ground wire fails in a two-prong outlet, the hot may still deliver electricity, which will find another way to ground, on the plug side of the outlet. This can include going through whatever is plugged-in (say a lamp) and through something else it is touching, like a table or person. Yes, there needs to be conductivity, so not all situations result in trouble this way.
If a ground wire fails in a three-prong outlet, the electricity should continue to flow through the other ground.
These tend to be most dangerous if electricity is flowing at the moment of a failure, after which a fuse or circuit-breaker should provide protection. If the failures occur before electricity flows, the additional conductivity of the object being powered matters.
Consider a movie trap scenario. The bad guy compromises the wiring, and leaves a radio on a shelf. The victim switches on the radio, and because of the construction of the radio, perhaps contact and construction with the shelf, or a puddle of water the person may be in (it is a movie trap). For at least some moments, the radio will try to flow electricity, but since the ground wire is cut, it has to go through the trap, either the shelf or person.
The scenario is only a bare stretch, and does happen without malicious configuration.
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