cant work this one out! Help please

[TicklyT]

It doesn't matter if you want to call the conductors 'Live', 'Line', 'Phase', 'Tom', 'Dick', 'Harry', 'Freeman', Hardy', 'Willis', 'Faith', 'Hope' or 'Charity' - the point is you cannot assign positive or negative polarity to the conductors of domestic AC power distribution in the way you can for a DC system.

I once knew a conductor called Harry - he used to work on the North Downs buses.

 

[Goldberg]

It doesn't matter if you want to call the conductors 'Live', 'Line', 'Phase', 'Tom', 'Dick', 'Harry', 'Freeman', Hardy', 'Willis', 'Faith', 'Hope' or 'Charity'

Yes it does - the popular term is "live". "Tighten the screw down firmly on the dick" has an entirely different meaning.

you cannot assign positive or negative polarity to the conductors of domestic AC power distribution in the way you can for a DC system.

Nobody has done that, and nobody has said that anybody has done that. You've introduced the positive/negative concept unnecessarily, and you're incorrectly limiting the attributes of polarity to that concept.

 

[TicklyT]

Yes, apparently I opened this can of worms when I wrote:-

.....Note this is a different issue to 'polarity'...

to avoid the issues of reversing the supply to permanent magnet DC motors, which isn't relevant to the OP's question.

In reply to Securespark, I wrote

That's probably where the confusion starts.... It's a convenient but inexact term to descibe a situation

because there is more than one definition of electrical polarity, leading to confusion for the uninitiated.

One definition describes positive and negative DC polarity, which may affect both the operation and safety of DC devices.
Another describes the line / live / phase and neutral of AC devices, a completely different property that has no effect on the operation of the device, but may compromise some safety aspects.

We need to be certain which definition we are describing because that is what the OP was asking about.

That's why I asked

Is it a leftover from those good old days of local DC power generation and distribution?

as that would tie up where the two definitions diverged.

 

[mattysupra]

Typically, single phase AC supplies use two conductors, and both should be considered live conductors.

Functionally, AC appliances don't care which way round these two conductors are connected, but it does have safety implications.

For various reasons, electricity supply companies try to maintain one of the conductors as near as they can to earth potential, and most refer to that conductor as 'Neutral', and the other conductor as 'live' or 'phase'.

In the UK, where ring final circuits are the norm, plug top fuses are fitted to protect appliance flexes etc. It's desirable to use a plug that only fits one way round in the socket, so the fuse is always in the 'live' conductor. The neutral conductor is considered less hazardous as it's potential should not vary much from earth potential.

In other countries individual sockets may be protected by fuses elsewhere in the fixed wiring. As the plug is not fitted with a fuse, a symmetrical plug which fits the socket either way round can be used.

Note this is a different issue to 'polarity'. Polarity is a property of DC systems, as used in automotive applications.

thanks for your 'normal' answer to my question. I understand how it all works but keep getting confused reading other posts that contradict each other!

Hence asking the question.

It also got confusing reading on past your post.

 

[securespark]

"Tighten the screw down firmly on the dick"

Didn't know you were into S&M...

 

[sparkypete1]

have to agree. i used to call an earth an earth, now they are cpcs!

 

[securespark]

They haven't always been "earth"... In the 14th Ed., first published in 1966, the cpc was referred to as the "earth continuity conductor".

The term "circuit protective conductor" came in with the 15th Ed., first published in 1981.

28 years ago.

 

[paulbanco]

....In fact, if we go back to our basic college days chaps, we all know that - is in fact + !, because electrons flow from negative to positive.

How F###ed up is that?

And you know why they taught all that ****e to us? Because the books had been printed before the thoery was proven to be the oppossite way around.

 

[ban-all-sheds]

....In fact, if we go back to our basic college days chaps, we all know that - is in fact + !, because electrons flow from negative to positive.

How F###ed up is that?

It isn't - the fact that electrons drift slowly from - to + does not mean that - & + are labelled the wrong way round.

And you know why they taught all that s***te to us?

It's not s***te, it's conventional current flow.

Because the books had been printed before the thoery was proven to be the oppossite way around.

Really?

When did you go to college? I distinctly remember being taught the difference between electron flow and conventional current 40+ years ago.

 

[paulbanco]

....at the speed of light? You must be SOME fast mover mate

 

[paulbanco]

I also went to college 40+ years ago, and that's what they told me then, presumably the laws of physics haven't changed since !

 

[ban-all-sheds]

....at the speed of light? You must be SOME fast mover mate

¿Que?

Where has the speed of light been mentioned?

I also went to college 40+ years ago, and that's what they told me then, presumably the laws of physics haven't changed since !

Some have, or at least have been refined.

But when you were at college they didn't teach you about electrons, and the difference between them and conventional current?

 

[paulbanco]

...I feel like I'm in the Monty Python 'argument sketch'

Yes, I couldn't agree with you more!, there are constant developments and changes in theory, none more so than in the field of sub atomic particle identification. If you cast your mind back to the way we were taught about atomic structure based upon Niels Bohrs planetary model of an atom with 3 parts, protons, neutrons and electrons, then compare it to the now known particles, over 20, thanks to particle accelerator research, you begin to grasp the fact that we seem to be guessing all the time at what actually happens at a sub atomic level.

Electron flow however, hasn't changed, and still remain the core of is it a particle?, or is it a wave?, hang on!, Eureka!! turns out it's both!!!

Right, here goes, last stab at this topic for me ( you're biting into my lunch time for Gawd's sake )

- and +, left and right, line up a load of atoms with free electrons ( a conductor ) introduce a positive charge on the right ( voltage, or potential difference ) and the negatively charged free electron on it's left will change state to positive so the move is from left to right, look at it though and visually, the flow would appear to be from right to left, right?

Jeez! I'm getting dizzy here

If you would like to while away a few weeks you could follow the following link, absolutely rivetting stuff ( not )

http://books.google.co.uk/books?hl=...ts=8S4l-pijsp&sig=pJCst6Kn8xeYO_pBQfsNUhMJTxo

Good luck.

Oh! and by the way, this all happens at the speed of light, not a slow progression at all, same as photon transmission ( light ), oh NO, let's not go THERE !

I can feel me quantum mechanics engine revving up!!!

 

[ban-all-sheds]

Oh! and by the way, this all happens at the speed of light, not a slow progression at all

electrons drift slowly from - to +

Propagation speed may well be of the order of the speed of light, but the actual electron drift velocity is in the order of mm/s.

 

[paulbanco]

Dead Right !

In fact, in an AC current there is absolutely no nett movement of electrons whatsoever, go figure THAT one out, EASY PEASY actually, because the electrons move with the electromagnetic field i.e. back and forth on the positive negative waveform !

.....which brings us right back to, are we observing a particle, or a wave?

Because the electromagnetic wave propogation function travels at the speed of light in a vacuum, about as fast as light in air, 96% the speed of light in an unshielded copper conductor and about 66% the speed of light in a co-ax cable.

Good innit?





I think we're gonna have to settle this by getting our wotsits out and having a dangle competition, mind you it beats working I suppose