OK so DC always flows one way so positive and negative terminals on a battery for instance are easy to understand.
So what about AC, which keeps changing direction?...how can one wire always be live and the other neutral?...surely they switch at the AC
frequency?
Always puzzled me that one....
The short explanation is...it's all BL@@DY BLACK MAGIC!! The only thing I understand about AC current is that if you make a leak in the
insulation, you'll let out the gray smoke (that's what's in the wires), and once the smoke is let out, it won't work any more.
Once you get to doubled-up voltages, then you apparently have two hot wires, one that's hot only half of the time (but in two directions!?) and
one that's neutral...but not always!
Go on...tell me that's no black magic!
Does it help if you think of the neutral as the ground/earth/negative?
BTW DC current flows from the negative to the positive!
I can explain but will be £19.99 p/m +VAT.
as posted above, DC does flow negative to positive..
When talking about AC, the live line is the one connected to the supply. And neutral is usually connected to earth (at the switch board) or maybe
seperate completely) Any switches and fuses should always be in the live wire. Every half a cycle the polarity of the supply changes - But this
doesn't mean the neutral becomes the supply thou.
not sure if that makes sense.. Easy to think of Live as Positive, and Neutral and Earth.
In AC the voltage is going from positive to negative, following a sinusoide. The distance from the neutral to the sinusoide is the voltage. So not
only it is changing from positive to negative, but also the voltage is going up and down.
Typically an AC current is generated by an alternator (hence Alternating Current?). In your car the rectifier transforms AC into DC.
I guess this a bit abstract information. A grafic will explain a lot. But I do not have that
The way I was told it (which may be a bit wrong), is
You have 3 wires in a plug.
Live - this is the power coming from the grid.
Earth - The local ground connection (usually within the house).
Neutral - a ground connection at the local sub-station.
Live will be at 230v relative to earth. Earth should be zero, and neutral will be a few volts, dependant on how far you are from the sub-station.
[Edited on 8/10/08 by David Jenkins]
Is it not because AC follows a sinusoidal wave i.e. like a roller coaster. It climbs up to the peak and then rolls down and into the negative before
climbing again. I know in simple small circuits you can install a capacitor so that when the current is "rolling down" the capacitor will
discharge and so the current climbs back up thus avoiding or smoothing the sin wave.
My understanding is also that instead of just sending current down the wire so it follows a sinusoidal wave pattern a few waves are sent split seconds
apart so that each wave slightly overlaps and, again, it stops the current from entering the negative side and smooths the whole thing out.
Thats my understanding.
Hmm, all very interesting.. how about 3 phase? 3 positives adn no negatives? Am I right or do I need to back to school??
The neutral wire is at a nominal potential of 0 volts (or should be anyway!), and the live wire has a sinusoidal voltage that varies between +155.5v at the positive peak and -155.5v at the negative peak if you are on a 110v supply. This gives 311v peak-peak, and the RMS voltage (which roughly means the equivalent DC voltage) is 110v.
quote:
Originally posted by mistergrumpy
My understanding is also that instead of just sending current down the wire so it follows a sinusoidal wave pattern a few waves are sent split seconds apart so that each wave slightly overlaps and, again, it stops the current from entering the negative side and smooths the whole thing out.
Thats my understanding.
quote:
Originally posted by coozer
Hmm, all very interesting.. how about 3 phase? 3 positives adn no negatives? Am I right or do I need to back to school??
Its quite simple really...
You plug the appliance in to the socket and turn it on... No need for ANY further explanation.
SIMPLE
quote:
Originally posted by nz_climber
as posted above, DC does flow negative to positive..
When talking about AC, the live line is the one connected to the supply. And neutral is usually connected to earth (at the switch board) or maybe seperate completely) Any switches and fuses should always be in the live wire. Every half a cycle the polarity of the supply changes - But this doesn't mean the neutral becomes the supply thou.
not sure if that makes sense.. Easy to think of Live as Positive, and Neutral and Earth.
Good debate...not many convincing answers though...
I'm not actually electrically clueless (despite the question LOL), I did C&G 236 pt2 many years ago so I'm pretty au fait with 3 phase
and most industrial/machinery type wiring....it's just this fundamental concept that kept me awake at night....(not really)
Thanks for the input.
wiring up a 3 phase machine or a 3 pin plug does not necessarily mean one needs to know the physics behind electricity.
electricity is very mysterious, I don't think anyone, even Lucas, can really say they know what it is but we can obxerve and measure its effects
and form theories about it which can be tested.
Thank god others have responded first!
I'm 26 and in my second year of my electrical installation apprenticeship (in the first year i got distinctions in all 6 modules, the only one to
do so in the college).
my plan is to finish the apprenticeship, then go straight into teaching.
as regards AC, i'll use one of my many anaolgies that make the 'boys' at college laugh:
imagine the 'live' (though subsequently called phase, and they now call it line) as blowing down a hose pipe. if you blow and suck 50 times
per second, but with the end blocked, then the energy goes no-where. however if you put say a fan in the way and a release the end, the fan will turn
(albeit one way, then the other). Basically, all the neutral is is a way of conpleting the circuit, or unblocking the hose pipe.
the problem comes if someone cuts the pipe halfway down, then the air escapes, the same as current does if there is a short circuit.
hope that's helped to confuse some people.
Martin
PS. I still have no clue how to wire my Tiger!!!
quote:
Originally posted by Alan B
Good debate...not many convincing answers though...
^^^
As a holder of an electrical engineering degree, that's my favourite one.
quote:
Originally posted by Liam
^^^
As a holder of an electrical engineering degree, that's my favourite one.
quote:
Originally posted by 02GF74
Current flow from positive to negative but inside the wire, the electrons flow from negative to positive.