If AC current changes direction (say) 60 times in a second, y do v have polarity in AC MAINS?

Answer 1

We don't.

There is no polarity to the mains.

The live and neutral refer to the actively driven terminal and the return path.

Answer 2

Ok, ok I see the point in your question. The problem is that you are picturing AC from a DC (direct current) perspective. Probably you think that the two terminals in a (e.g.) TV plug are similar to a battery's + and -. This is a common error, or at least when I teach it, it takes one or two explenations to really bring it home.

Now, you may know that the wires in a home socket have two names: LIVE and NEUTRAL. LIVE carries the Current, while NEUTRAL is grounded, i.e. 0 Volts and hence the electrons making up the Current would "like" to "go" to such a situation: a place where they have no electrical energy.

For a second get your mind off this and imagine two water pipes, running parallel to eachother, but independent of eachother. One of the pipes has water flowing through it (we'll call it pipe A), while the other is empty (pipe B). Now, what happens if you connect a pipe (let's call it pipe C) between these two?

Water flows from pipe A to pipe B, of course!

Would it make a difference if the water inside pipe A had been flowing in the opposite direction?

No. As long as pipe B is empty (or having a lesser flow of water for that matter), water will always flow from pipe A to pipe B.

Now, imagine pipe A to be the LIVE terminal, and pipe B to be the NEUTRAL terminal. The device you connect to the socket acts in the same way that pipe C does: it gives the possibility for current to flow between the LIVE and NEUTRAL.

In the same way as the water's direction in pipe A does not influence the water's flow, so the flow of Current from LIVE to NEUTRAL is independent of the direction of Current flow in the LIVE wire.

And current flows only if there is a potential difference. Hence the difference in Voltage between the LIVE and NEUTRAL terminals.

That is why birds do not end up electrocuted when perching on Electrical Cables. Since both legs are touching the (e.g.) LIVE wire, Current does not have an "incentive" to move through the bird's legs. It would be a different story should one leg be on the LIVE wire, and the other touching the ground!

Hope to have been of help.

Answer 3

Although the new plugs are called "polarized", I think that is a misleading term. Only DC electricity is polarized.

However, either DC or AC, you need a closed circuit to make the current flow. That is a continuous loop of wire that comes from the generator, to the appliance and back to the other pole of the generator. Even an AC generator has 2 poles (I am neglecting 3 phased here and assuming single phase, which is what most household power is). But I think engineering practice is to ground one of those poles by actually connecting it to a rod stuck in the ground. This allows true Earth ground reference for the power. Otherwise, the 120 volt power could be made up of one pole at 10120 volts and the other pole at 10000 volts. As long as the difference between the poles is 120, then it is 120 volt power, but it is nice not to have the whole power grid drifting above Earth ground at some absurd bias.

Anyway, polarized plugs identify the "hot" and "ground" wire, where the "hot" one is the one NOT connected to ground. In theory, you could touch the "ground" wire and not get a shock (but don't try that), because it is always at ground potential, or 0 volts. The "hot" wire is alternating between + and - 120 volts and touching that one could shock you. So it is good to treat them differently.

Answer 4

As stated in the previous post only one wire actually carries a charge. But the reason for polarization has more to do with the internal electronics of the item you are plugging in. As you may have noticed not all items are polarized. Digital electronics like to have current flow in the right direction so operations happen in the correct order. Most current items have at least one diode(usually many many more), diodes limit the current flow to only one direction. This limiter effectively converts AC current to DC current.

If everything runs on DC why have AC at all? AC is much easier to transport over long distances with much less bleed off of the transmitted power.

Answer 5

the electric frm the transformer farm put out 3 phase useing 220 voltage to make 440 volt lines to the phone pole and to the pole transformers and inturn they change it into 220 three phase that is two 110 volt lines and one ground

and your stove runs on 220 volt three phase and if the polarity was wrong one would get shocked or worse or the stove might catch fire . a large air condidisiner runs on 220 three phase too polarity is inportant there too.

you may wonder how can wires carry that much and be safe? and birds do not fry when they land on them. the answer is cause there is three positive cables running to the polr and one gound wire and they are seperated by air so the birds so not fry if they land on the wire only if they touched two wires at the same time then they would be fryed up extra crispy

if there is no polarity why are plugs polarized ?

Answer 6

determine by the country
actually there is no polarity in the AC current but

IF one of the cable is grounded then there is signal (with test pen)

from the one which is not grounded

I know its not a clear answer but we studying electrical 4 years ^_^

Answer 7

Not normally, but the supply system is grounded/earthed at the local transformer and any underground overall cover cable joints to which the neutral and ground/earth wires are eventually connected. It is therefore good to have a polarised connector particularly where single pole switching/fuse protection is used. A 2 pin plug/socket (ungrounded/earthed) are not usually polarised.

Answer 8

we dont have polarity in ac current or voltage actually
it s in dc current only

Answer 9

THERE IS NO POLARITY IN AC SUPPLY. IT ONLY HAS PHASE AND NEUTRAL