So in England we have the ground prong so our cables are all the same, however I know in the states and other places they don’t, so how come no damage is caused if the positive and negative are the wrong way around?
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US outlets have one slot slightly larger than the other, and a ground pin (for a standard 120v/15a outlet)
The small slot is the hot, 120 volts AC. The larger slot is the neutral, which returns the current to the source.
There are three styles of plugs that fit this outlet.
One has two identical small prongs and can be installed in either orientation.
Another has a small prong and a big prong and can only be inserted in one way (“polarized”
A third style has two small prongs and a ground pin and can only be inserted in one way.
For the first type, it is only used on devices that are ungrounded and that don’t have any unique wiring. Most of the time it is an AC to DC transformer that has both the hot and neutral insulated, and is in a plastic enclosure.
The second type is ungrounded as well, but is built in such a way that it matters which side is hot. For instance, a lamp with an Edison screw base is polarized. That’s because the screw threads should be on neutral, and the power switch should interrupt the hot. If it was reversed, it would still work. However, if you turned the lamp off and clumsily replaced a bulb, you might get shocked by touching the screw threads. Not likely, but not safe. This is common in a lot of small appliances that have plastic enclosures, because the switching and internal fuses are laid out assuming the same side is always hot.
The third type is when there’s a metal chassis that needs to be grounded for safety reasons. Even if it’s an AC to DC power supply that doesn’t care about polarity, the existence of the ground pin essentially forces the same side to always be hot. Note that because of this feature, these plugs never have the larger prong on the neutral like the second type – it would be unnecessary.
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