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?
In: 22
For many appliances, it doesn’t really matter if hot and neutral are reversed.
In some cases, it does, and where it does matter, a ground pin or a larger neutral connector will be used to ensure polarity.
Exactly like the other poster said. Our outlets are polarized with one slot slightly larger than the other. For applications where polarity is important, the device’s plug has one blade larger than the other. Some simple or older devices where polarity doesn’t matter may have a plug with both blades the same size.
AC is alternating current… which prong is positive and which is negative intentionally goes back and forth 50 or 60 times a second, depending on where you live. It’s why your electrical panel makes a humming or buzzing noise.
As a result, most appliances don’t care which is which because it’s always changing anyway. They’re built to take electricity traveling in either direction because that’s exactly what happens. For them, flipping around the plug is no different than having waited 0.01 seconds before plugging it in. Who cares?
Nevertheless, one prong is definitely the more dangerous of the two, and so some appliances are designed around this for safety reasons. They’ll have one prong intentionally bigger, or have a grounded plug (actually safer!) so that it only plugs in one way. Then the safety design will play to the more dangerous of the two main prongs.
Wall outlets have AC voltage and consist of three wires: phase, neutral and protective earth. Phase and neutral carry the current that powers things, protective earth is for safety for devices built in a way that makes it necessary.
The voltage on the wire called phase moves up and down, if you were to draw it it would show a sinusoidal curve that goes as much positive as it goes positive, moving up and down 50 or 60 times per second, depending on the country. The voltage on the neutral wire, on the other hand, stays basically at 0.
Now imagine a room split in half, one half of it continuously moves up and down, while the other half is planted. If you put a camera in one of those halfs, oriented at the other half, you will see the same thing regardless of which part you put the camera in: half a room moving up and down.
That is what delivers the energy to the device: the difference between phase and neutral. And for that aspect, the difference from one to the other looks the same no matter which one is your reference. So, in general and from a merely functional point of view, it doesn’t make a difference.
Alternating current does not have positive and negative. It has a hot and a neutral. For AC power it generally doesn’t matter which way something is plugged in.
It’s Alternating current, meaning it goes both directions (for lack of a better layman term).
It’s AC power, so most of the time it doesn’t matter because it goes + – + – + – 50 times a second (50Hz) for you in Europe, and 60 times a second (60 Hz) in the US and Canada. If you change that to – + – + – +, it doesn’t really change anything.
Certain devices can be polarized, though, so they will have one prong be slightly larger, and the corresponding hole is also slightly larger, so you can’t plug it in backwards. If you look at an American outlet, you can see the left hole is slightly taller than the right.
Even in the UK you’ll very frequently see IEC C7 connectors which are an ungrounded and non-polarized AC connector that looks a bit like a figure of 8. https://wikipedia.org/wiki/IEC_60320
When I moved to the uk in the 80s and discovered their plugs, I used to rant about them.
– they were unnecessarily huge. And hard. And painful.
– the electrical appliance has an on/off switch.
– it also has a fuse in it.
– the plug itself has a fuse in it.
– the wall outlet it plug into has an on/off switch.
– the outlet it connected to a central circuit breaker or fuse.
Talk about overly paranoid and completely unnecessary. To make matters more infuriating, I would see people watch tv. Then after watching it, they would (this is where I usually got red-faced and loud)
UNPLUG THE DAMN TV FROM THE WALL.
<I feel the old rants starting to build in my head again 40 years later as I write this). Breathe. Calm down.>
Then I lived there for a few years. And slowly started understanding a few things. The big shock to my indignation came from the calm explanation that, “where you come from, houses are what, 30 years old? Over here they could be 400 years old. The wiring is likely 100 years old. Every week somewhere in the uk a house burns down because of old wiring. So yeah. We need a few extra safety features in our stuff “. Then I learned that many electrical devices drew power even when unplugged, and that unlike where I come from where electricity is as cheap and plentiful as the rivers and lakes that generate it, over in the uk they burn coal or use nuclear power plants to create the stuff. So it’s not cheap, nor is it plentiful. The power plants have to keep a schedule of football match days and times to know when the power demand is going to peak, because everyone puts the kettle on at the same time.
So I learned a few lessons about the uk and their humongous Lego foot puncturing plugs.
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.
Latest Answers