If alternating current goes both ways, why do some plugs only allow you to put them in one way?
In: Engineering
Safety. AC (hot wire) goes both ways, but it needs a center point to push-pull against. We call that center the “neutral” wire, which goes back to the power station, but also to earth-ground.
The metal cases of appliances also have a grounding/bonding wire, so that if a wire ever came loose inside the power would go to ground through that wire, instead of through you when you grab the handle. That’s different from the neutral though.
The neutral and ground are connected, so that the center point “neutral” can’t float to some undefined value, with the hot going along for the ride. Why it might float is beyond what I can explain here.
Reversing hot and neutral would connect the case of the appliance to power, through the neutral-ground link in your power panel. Risk of death.
Some appliances don’t have a ground and the hot and neural can be flipped because there’s no metal casing or polarity sensitive devices inside (some kinds of motors care about polarity, etc.).
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