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Old 01-14-2007, 09:25 AM   #1
keyboardcowboy
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Question Alternating current & neutral wire

Our electrical suppply in our home is alternating current (a.c)
right?
Since a.c current keeps on changing direction why is it that in our home only the live wire carry electricity while the neutral wire is neutral.Shouldn't the neutral wire also be charged half the time.The live wire can be both positive and
negative and so can the neutral wire
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Old 01-14-2007, 11:36 AM   #2
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Default Re: Alternating current & neutral wire

Yes homes use AC. DC would use large cables to prevent high current loss.
You can reverse the hot with the neutral, it's just not safe to do.
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Old 01-14-2007, 12:01 PM   #3
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Default Re: Alternating current & neutral wire

But the neutral wire carries no charge,i have touched it and didn't get any shock whereas the hot wire shocks
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Old 01-14-2007, 12:20 PM   #4
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Default Re: Alternating current & neutral wire

well there goes my theory on electronics.
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Old 01-14-2007, 12:56 PM   #5
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Default Re: Alternating current & neutral wire

well simply...live carries ac current to the equipment and neutral takes it back
you can reverse live and neutral at the plug, otherwise plugs would only fit in one way

but you should not assume that neutral does not carry a charge. you should not assume that any circuit is properly wired and safe until it has been proven to be so.
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Old 01-14-2007, 07:46 PM   #6
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Default Re: Alternating current & neutral wire

Well, if you consider the neutral wire as a middle point, you shure can conect either a negative voltage to the live wire or a positive compared to the potential of the neutral wire.
This is not comparable with an simple battery sheme, where you have only one positive potential. This is not symetrical.
IMHO AC it is not the same like switching the polarity of a battery. Immagine two bottle, one is positive the other negative compared to the neutral.
If you conect alternating on of those bottles to the live wire, you have a symetrical AC current, but no voltage on neutral, if all apliances are safe and ok.
This is exactly, what is the AC current from the mains.
If you charge two capacitors, the one with the first halve of the the sine wave (positive compared to neutral), the other with the second halve you have the doubled line voltage between them.
google a littel abouth symetrical sine waves, or just pic an shematic from a symetricaly powered op-, pre- or poweramplifier. Than you will easily see, what is the difference betwen symetric and none symetric currents.
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Old 01-21-2007, 09:08 AM   #7
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Default Re: Alternating current & neutral wire

but what happens when AC alternates shouldn't the live wire become neutral and the neutral wire live then.
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Old 01-23-2007, 06:18 AM   #8
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Default Re: Alternating current & neutral wire

The white wire is the GROUNDED wire, the bare copper wire is the GROUNDING wire. They both connect to the neutral buss in the service box. Power does not come from the ground. If you grab the white wire after a load and your body provides sufficient earth ground, you are DEAD.

Three wires come into the service box: black 115V, red 115V, (each connecting to a separate buss) and the bare grounded wire. Every other circuit breaker on one side of the service box connects to the opposite hot (115V) buss. A 220V breaker occupies two spots on one side of the box taking two 115V lines to a 220V outlet.

AC current alternates between positive and negetive, the negetive is still positive with respect to ground. If the current stopped flowing every time the cycle went negetive you would have a half wave rectifier.

Anyone may feel free to correct me if I am wrong, I have very thick skin...

Last edited by Lonnie; 01-23-2007 at 06:20 AM..
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Old 01-23-2007, 10:20 AM   #9
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Default Re: Alternating current & neutral wire

Humm A common enough question, and a not so easy one to answer


Quote:
but what happens when AC alternates shouldn't the live wire become neutral and the neutral wire live then.
No current just changes direction,
The Active line potential difference in volts with respect to Neutral line goes negative or positive of our Neutral return line.

The Neutral line is connected at some point to true earth, the ground on which you stand


Current does flow in the neutral and the ground as well
it gets very complex how it all works

If you want little more read what I have posted below, I will see if I can find some links that explain it all better then I have.

Bear in mind I am going to lie to you to some extent and yeah its a long winded answer but I hope it makes things clearer

The neutral wire is connected at some point to true earth
the earth (as in ground you stand on) is used as the return wire for the AC System


(Same idea as a car battery.....just connect one side to the battery to frame of the car, this is dc thought and yes in the past positive of battery has been connected to the car frame ...there are technical reasons why this scheme was used)

So the only way you will get a shock is to touch the active wire.

Why cause anything else you touch is at earth potential
The same potential as neutral line, its earthed


Now if you are insulated and you are not touching anything that is earthed and hold on to the Active wire...trust me you will not get a shock.... you will not even get a tingle
In short you wont be aware of it at all


BUT you will be live at potential difference in volts of 110 Volts or 240Volts AC WITH RESPECT TO EARTH or the neutral.

****** FOR SAFETY'S SAKE DO NOT TRY THIS *********



Why is it birds can sit on power lines?

Cause they have no connection to earth therefore they will exist at say 110 volts with respect to earth

This is how people get killed
Not knowing they are live then touching say a water tap or something that is earthed

Most common for this is washing machines who's metal case has become live due to wear on the active line (or whatever)

We now come to the next part,

The reason you get a shock is because of CURRENT flow.

Current flows via your body between the Active and Neutral (usually earth in the case above.)
You must of course be connected to both


The key thing here is that POTENTIAL DIFFERENCE measured in Volts
and CURRENT measured in Amperes

Are two different entities with electricity
(or you should for you mind model consider it that way)

So PD Voltage exists across two points
Current Amps flows from one point to the other via a conductor.

A conductor is anything that will allow current to flow between the PD source
All conductors will have some opposition, resistance to current flow


Now back to our bird

If I take an insulated copper wire, bare one end and tie it to the birds neck then take the other end bare that and stick it in the ground with a metal stake.
Then let the bird fly up and land on the power line, it will now become the conductor between active and neutral...and one fried bird
or we can think of the bird as a resistive load on the active and neutral.

So to summarize;

In order to get current flow through a conductor we need a potential different between to points. the neutral and everything else is at or very close to the same PD therefore no current flow..well not enough to give you a shock anyway

As to AC

If I take two 9 volt batteries (B1 B2) and tie the positive of B2 to the negative of B1
(this is called series aiding)

Then call that point neutral, zero volts or earth.
(we will pretend this point is connected to the earth we stand on and that the other end of the lt bulb is stuck in the ground)


I then take a lt bulb and connect one side to this point 0V neutral earth and then connect the other side of the light bulb "alternatively" to first the positive of B1 then the negative B2 and keep repeating this action I will have alternating current flow in the light bulb.


most of the above is only to convey the concepts, its not the technical reality of things OK

It could have been better structured too.

Hope it helps you and doesn't confuse you

was looking for some good links that could explain this simply but as yet none Iam happy with ..here's a wiki HIH

wiki

Cheers
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Old 02-04-2007, 11:04 AM   #10
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Default Re: Alternating current & neutral wire

that cleared my head a bit
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Old 02-04-2007, 12:43 PM   #11
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Default Re: Alternating current & neutral wire

Quote:
Originally Posted by willawake
you can reverse live and neutral at the plug, otherwise plugs would only fit in one way
Actually that's not true. Most mains plugs will only fit into the socket one way round. The UK standard 3-pin plug has an earth pin that ensures you can only put the plug in the right way round. Likewise, in the US the pins are angled so that you can't put the plug in upside down. It's a very bad idea to reverse live and neutral, as the devices will be set up to take current from the live and pass it through to the neutral. If you put it in backwards, the capacitors and regulators will be powered backwards and could cause an explosion!

I remember a demonstration on TV where they rigged up a mains wire so you could switch off either the live or neutral lines. They switched off the neutral, the connected device (a table lamp) went off - but checking with an electrician's test probe, there was still current going to the lamp. Then they turned on the neutral line and switched off the live - this time, the test probe gave no indication of the appliance being live.

My father was once asked by a group of students why birds don't get electrocuted when sitting on power lines, and gave the no-ground explanation. Later on, he saw those students by a railroad track, jumping on and off the live rail - without getting electrocuted!
Speaking of which, regarding rail/tram tracks... usually, the neutral return line is through one of the running rails. If you step on the neutral rail (even while grounded) you will not feel anything - but step on the live rail, and you'll get a shock. This is especially noticeable with trams that get their power from an overhead wire. Touch the overhead wire and you'll get shocked, but you won't get shocked if you touch the rails - even if a tram has just passed!

Last edited by Tom41; 02-04-2007 at 12:50 PM..
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Old 02-04-2007, 02:05 PM   #12
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Default Re: Alternating current & neutral wire

In Germany at least, the wallplugs are not coded in any way. So you can plug the conector in any direction and alternating the neutral and live wire.
The conector features two safety ground contacts, wich do conect the device to ground regardles if it is rotated by 180
Some HIFI enthusiasts marke their equipment, to avoid different conected device in their stack.
If this benefits in any way, i have no clue.
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Old 02-04-2007, 02:14 PM   #13
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Default Re: Alternating current & neutral wire

its the same all over europe i believe. except for those countries that follow the UK method, malta, cyprus? (which i forgot...)

i doubt they would do UK specific psus on equipment these days. just add a different plug. Interesting also that UK plugs have a fuse whilst european do not.
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Old 02-04-2007, 03:28 PM   #14
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Default Re: Alternating current & neutral wire

Quote:
Originally Posted by gonzo0815
In Germany at least, the wallplugs are not coded in any way. So you can plug the conector in any direction and alternating the neutral and live wire.
The conector features two safety ground contacts, wich do conect the device to ground regardles if it is rotated by 180
Some HIFI enthusiasts marke their equipment, to avoid different conected device in their stack.
If this benefits in any way, i have no clue.
If the hot and common are reversed and the operator is grounded, a slight tingling sensation can be felt when the equipment's metal case is rubbed.
I have read this posted concerning metal comp cases here in The States.

I check my outlets with a test probe before hooking up gear. I was told to do it long ago and I still do it.
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Old 02-04-2007, 04:12 PM   #15
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Default Re: Alternating current & neutral wire

isnt that actually when the ground is poor or non existent?
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Old 02-04-2007, 04:40 PM   #16
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Default Re: Alternating current & neutral wire

I would say yes will, when my body offers a lower resistance ground than what is offered at the socket. I have been shocked by electric drills and impact wrenches that had metal bodies but only when the hot & common were reversed. My feet / boots were wet as were my hands.
Over at AnandTech a fello had the hot / common reversed and was getting buzzed by his comp case. The wall socket was ungrounded.

I remember carlo was running ungrounded at his home. Gabe explains virtual grounding on page two. It is a way to protect connected, yet ungroundable hardware. http://hardwaresecrets.com/article/18

I was told that proper grounding offers a path to the static charge built up by spinning opticals and HDDs.
I don't know how true it is but I did read that some of the early suspended HDD failures were due to being ungrounded. Some HDDs do have a male blade connector for grounding.
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Old 02-04-2007, 04:50 PM   #17
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Default Re: Alternating current & neutral wire

damn thing is when i receive that no ground buzz i usually am under an office table and bang my head in reaction. i am a little short on braincells after all these years, i hope all the good ones are in the center and dont get damaged from this.

i have soldered a few boards on an ungrounded socket before i realised. can get a buzz if my face touches some metal on the board while i am doing that. i will measure the voltage coming off the tip sometime......
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Old 02-04-2007, 04:59 PM   #18
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Default Re: Alternating current & neutral wire

I have tried it, bit the voltage is probably not measuable with a common DVM. probably you need the oscope to carry with you.
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Old 02-04-2007, 08:03 PM   #19
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Default Re: Alternating current & neutral wire

There should be near full voltage between Live and Earth, and no more than 0.5VAC between Neutral and Earth. If you get anything different, call an electrician.
A warning for service personnel on a 2-pin AC adaptor telling that the input is not polarized and the fuse may "appear" in the neutral position.
I have seen 2-pin figure-8 connectors on AC adaptors which a corresponding lead can only be inserted one way (one side is square with the other side round).
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Old 02-05-2007, 10:08 AM   #20
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Default Re: Alternating current & neutral wire

The connectors used in Sweden can be inserted any way. (while still being grounded)

I do not understand how there can be a difference really, it's AC afterall, one big sinus wave moving between a couple hundred volt + and -

If someone could sometime explain to me how AC _really_ works I'd give them a cookie

I still to this day have big problems understanding it...
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