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Electricity - Physics Forum

Electricity - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 04-29-2007, 04:56 AM
Brian
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Default Electricity



I have a somewhat practical question about electricity - namely household
electricity. I have read, and finally understand a bit about electricity.
From what I have read, The hot wire carries the energy; the neutral wire is
a ground, and the ground wire is there in place of a short; to safely
dissipate the hot current to the ground.

What I don't understand is, in most places I've read, and from my
understanding, what actually happens with electricity is electrons want to
flow from the negative terminal, through the load, to the positive terminal.

So, is the hot wire in a house the negative terminal, and the neutral wire
the positive terminal? It is unclear to me. With this, do electrons want to
flow from the green ground to the hot wire? Or is all this vice versa. If
so, what is going on with the hot wire? If it is the positive terminal,
does the electric power wires delivering the hot wire simply try to pull
electrons to it, creating the current through the load?

Brian

Brian


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  #2  
Old 04-29-2007, 10:19 AM
Prai Jei
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Default Electricity

Brian (or somebody else of the same name) wrote thusly in message
<vAVYh.856$YQ1.538@trndny02>:


Assuming the domestic electricity is AC even where you are, the "hot" wire
(we call it live over here) constantly alternates between positive and
negative with respect to the neutral wire.

The neutral wire is earthed (grounded) at the generating station, or at
least at the last transformer along the way. This is to be the expected
return path for the current, with the ground wire carrying no current at
all but merely there as a safety measure. The grounding of this wire is
often overlooked, but is a vital point. Without this grounding, an
additional ground wire at the appliance would do no good at all since it
would not be part of a complete circuit.

The live wire is at an alternating but generally high potential with respect
to both the neutral and ground wires. Under normal operation conditions
this potential will force alternating current through the load and into the
neutral wire. Under fault conditions there will be a short circuit (excess
current) between live and ground, which by design will blow a fuse or throw
a trip to cut the circuit (disconnecting the live wire) in the shortest
possible time.

The more modern earth leakage detectors will respond to even partial fault
conditions (small but still *wrong* currents in the ground wire) and throw
a trip.
--
Two-colour printing (red/black/blue/green) available

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  #3  
Old 04-29-2007, 10:19 AM
Prai Jei
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Default Electricity

Brian (or somebody else of the same name) wrote thusly in message
<vAVYh.856$YQ1.538@trndny02>:


Assuming the domestic electricity is AC even where you are, the "hot" wire
(we call it live over here) constantly alternates between positive and
negative with respect to the neutral wire.

The neutral wire is earthed (grounded) at the generating station, or at
least at the last transformer along the way. This is to be the expected
return path for the current, with the ground wire carrying no current at
all but merely there as a safety measure. The grounding of this wire is
often overlooked, but is a vital point. Without this grounding, an
additional ground wire at the appliance would do no good at all since it
would not be part of a complete circuit.

The live wire is at an alternating but generally high potential with respect
to both the neutral and ground wires. Under normal operation conditions
this potential will force alternating current through the load and into the
neutral wire. Under fault conditions there will be a short circuit (excess
current) between live and ground, which by design will blow a fuse or throw
a trip to cut the circuit (disconnecting the live wire) in the shortest
possible time.

The more modern earth leakage detectors will respond to even partial fault
conditions (small but still *wrong* currents in the ground wire) and throw
a trip.
--
Two-colour printing (red/black/blue/green) available

Interchange the alphabetic letter groups to reply
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  #4  
Old 04-29-2007, 04:58 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Electricity

Dear Brian:

"Brian" <[Only registered users see links. ].NO_SPAM> wrote in message
news:vAVYh.856$YQ1.538@trndny02...
....

Prai Jei has given you a thorough answer. Just a little more...

The hot wire is so named because it has voltages positive 60
times a second, and negative 60 times a second. Domestic 240vac
(in the USA), both power wires are hot (one being positive, the
other negative, then swapping). Usually an electric dryer, or
home A/C unit runs on 240 vac.

The neutral wire should only have at most couple of volts AC
between it and the ground wire. Any more than this and there are
problems in your wiring.

The green ground wire is strictly for protection. There are
devices called "ground fault interruptors" (GFI) that monitor an
entire circuit (more than just an outlet usually) for current
above threshold on the ground wire, and will trip a breaker
cutting off the suppply voltage. You usually find these in /
near bathrooms.

David A. Smith


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  #5  
Old 04-29-2007, 04:58 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Electricity

Dear Brian:

"Brian" <[Only registered users see links. ].NO_SPAM> wrote in message
news:vAVYh.856$YQ1.538@trndny02...
....

Prai Jei has given you a thorough answer. Just a little more...

The hot wire is so named because it has voltages positive 60
times a second, and negative 60 times a second. Domestic 240vac
(in the USA), both power wires are hot (one being positive, the
other negative, then swapping). Usually an electric dryer, or
home A/C unit runs on 240 vac.

The neutral wire should only have at most couple of volts AC
between it and the ground wire. Any more than this and there are
problems in your wiring.

The green ground wire is strictly for protection. There are
devices called "ground fault interruptors" (GFI) that monitor an
entire circuit (more than just an outlet usually) for current
above threshold on the ground wire, and will trip a breaker
cutting off the suppply voltage. You usually find these in /
near bathrooms.

David A. Smith


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  #6  
Old 04-29-2007, 08:07 PM
Brian
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Posts: n/a
Default Electricity

OK; so this still does not completely answer my question. Every source I
read says the electrons (or current) want to flow from the negative to the
positive; my understanding from what you all say is that the circuit
alternates - when the AC is negative, electrons flow from the hot wire to
the neutral wire. When it is positive, that would mean the electrons flow
from the neutral to the hot wire?... I understand fully the purpose of the
green (or copper) wire. I'm still trying to understand how the electrons
flow. I guess the literature I have read saying electrons actually flow
from negative to positive is for DC. Like in a car battery. So, how about
for AC?

Brian
"N:dlzc D:aol T:com (dlzc)" <[Only registered users see links. ]> wrote in message
news:Z84Zh.9258$[Only registered users see links. ]...


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  #7  
Old 04-29-2007, 08:07 PM
Brian
Guest
 
Posts: n/a
Default Electricity

OK; so this still does not completely answer my question. Every source I
read says the electrons (or current) want to flow from the negative to the
positive; my understanding from what you all say is that the circuit
alternates - when the AC is negative, electrons flow from the hot wire to
the neutral wire. When it is positive, that would mean the electrons flow
from the neutral to the hot wire?... I understand fully the purpose of the
green (or copper) wire. I'm still trying to understand how the electrons
flow. I guess the literature I have read saying electrons actually flow
from negative to positive is for DC. Like in a car battery. So, how about
for AC?

Brian
"N:dlzc D:aol T:com (dlzc)" <[Only registered users see links. ]> wrote in message
news:Z84Zh.9258$[Only registered users see links. ]...


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  #8  
Old 04-29-2007, 09:46 PM
andy-k
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Default Electricity

"Brian" wrote:

For Alternating Current supplies, the direction of electron flow
Alternates -- i.e. electrons first move one way around the circuit, then
reverse their movement and flow the other way around the circuit, and then
reverse again and so on. The frequency given for the AC supply is the number
of full cycles (i.e. reversal and reversal back again) that the flow makes
in every second. Consequently it would be inappropriate to consider either
the hot or the neutral wire to be negative or positive since this latter
status keeps reversing. Rather the neutral wire is the wire that is grounded
at the generating station, and so the one that it isn't dangerous to touch
(unless you have faulty wiring). If you touch the hot wire, then *you*
complete the circuit down to ground and back to the generating station
through the ground -- hence 'hot'.



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  #9  
Old 04-29-2007, 09:46 PM
andy-k
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Posts: n/a
Default Electricity

"Brian" wrote:

For Alternating Current supplies, the direction of electron flow
Alternates -- i.e. electrons first move one way around the circuit, then
reverse their movement and flow the other way around the circuit, and then
reverse again and so on. The frequency given for the AC supply is the number
of full cycles (i.e. reversal and reversal back again) that the flow makes
in every second. Consequently it would be inappropriate to consider either
the hot or the neutral wire to be negative or positive since this latter
status keeps reversing. Rather the neutral wire is the wire that is grounded
at the generating station, and so the one that it isn't dangerous to touch
(unless you have faulty wiring). If you touch the hot wire, then *you*
complete the circuit down to ground and back to the generating station
through the ground -- hence 'hot'.



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  #10  
Old 04-30-2007, 02:27 PM
PD
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Default Electricity

On Apr 29, 3:07 pm, "Brian" <[Only registered users see links. ].NO_SPAM> wrote:

They flow back and forth, sometimes from the hot to the neutral,
sometimes from the neutral to the hot. Hence the term "alternating
current". Note that "hot" does not refer to current, it refers to
voltage. Though the neutral line is at 0V nominally, current must flow
through both hot and neutral terminals in a closed loop circuit.
Current (electrons) does not get "used up" in the load, the energy
does.



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