You may face some confusion when reading AC (Alternate Current) things in basic Electronic or Electric writings. As unlike water current we cannot see actual movements of Electrical Current(s) we must believe what the writer says. But most writers of the writings on AC (Alternate Current) things are not quite sure of it by themselves, I assume, or taking it for granted (the readers already know it).
For instance
Ground and neutral - wiki
As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.
Contents
Definitions
Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment (the terms "ground" (North American practice) and "earth" (most other English-speaking countries) are used synonymously here). Under normal conditions, a grounding conductor does not carry current.Neutral is a circuit conductor that carries current in normal operation, which is connected to ground (or earth).
In a polyphase or three-wire (single-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors. By this definition, a circuit must have at least three wires for one to serve as a neutral.
-----
Mains electricity - Wiki
|
This article needs additional citations for verification. (May 2009) |
:
:
Building wiring
In most countries, household power is single-phase electric power, with two or three wired contacts at each outlet.- The live wire (also known as phase, hot or active contact), carries alternating current between the power grid and the household.
- The neutral wire completes the electrical circuit by also carrying alternating current between the power grid and the household. The neutral is connected to the ground, and therefore has nearly the same electrical potential as the earth. This prevents the power circuits from increasing beyond earth voltage, such as when they are struck by lightning or become otherwise charged.
- The earth wire or ground connects the chassis of equipment to earth ground as a protection against faults (electric shock), such as if the insulation on a "hot" wire becomes damaged and the bare wire comes into contact with the metal chassis or case of the equipment.
For more details on this topic, see Ground and neutral.
----
Wiki itself notices that the above two articles are not good stuff. Let us take some better descriptions.
From: http://www.dummies.com/how-to/content/alternating-current-in-electronics-hot-neutral-and.html
Alternating Current in Electronics: Hot, Neutral, and Ground Wires
Before you start working with line voltage in your electronic circuits, you need to understand a few details about how most residential and commercial buildings are wired. The following description applies only to the United States; if you’re in a different country, you’ll need to determine the standards for your country’s wiring.Standard line voltage wiring in the United States is done with plastic-sheathed cables, which usually have three conductors. This type of cable is technically called NMB cable, but most electricians refer to it using its most popular brand name, Romex.
Two of the conductors in NMB cable are covered with plastic
insulation (one white, the other black). The third conductor is bare
copper. These conductors are designated as follows:- Hot: The black wire is the hot wire, which provides a 120 VAC current source.
- Neutral: The white wire is called the neutral wire. It provides the return path for the current provided by the hot wire. The neutral wire is connected to an earth ground.
- Ground: The bare wire is called the ground wire. Like the neutral wire, the ground wire is also connected to an earth ground. However, the neutral and ground wires serve two distinct purposes.The neutral wire forms a part of the live circuit along with the hot wire. In contrast, the ground wire is connected to any metal parts in an appliance such as a microwave oven or coffee pot. This is a safety feature, in case the hot or neutral wires somehow come in contact with metal parts.Connecting the metal parts to earth ground eliminates the shock hazard in the event of a short circuit.
The three wires in a standard NMB cable are connected to the three prongs of a standard electrical outlet (properly called a receptacle). As you can see, the neutral and hot wires are connected to the two vertical prongs at the top of the receptacle (neutral on the left, hot on the right) and the ground wire is connected to the round prong at the bottom of the receptacle.
You can plug a two-prong or three-prong plug into a standard
three-prong receptacle. Two-prong plugs are designed for appliances that
don't require grounding.Most nongrounded appliances are double-insulated, which means that there are two layers of insulation between any live wires and any metal parts within the appliance. The first layer is the insulation on the wire itself; the second is usually in the form of a plastic case that isolates the live wiring from other metal parts.
Three-prong plugs are for appliances that require the ground connection for safety. Most appliances that use a metal chassis require a separate ground connection.
There is only one way to insert a three-prong plug into a three-prong receptacle. But regular two-prong plugs, which lack the ground prong, can be connected with either prong on the hot side.
To prevent that from happening, the receptacles are polarized, which means that the neutral prong is wider than the hot prong. Thus, there's only one way to plug a polarized plug into a polarized receptacle. That way, you can always keep track of which wire is hot and which is neutral.
-----
The underlines made by me.
- Hot: The black wire is the hot wire, which provides a 120 VAC current source.
- Neutral: The white wire is called the neutral wire. It provides the return path for the current provided by the hot wire. The neutral wire is connected to an earth ground.
These explanations on AC (as we are not talking about Ground so I omit it ) are very common. You can find them through internet easily. You will try as I did.
But when you consider the AC (Alternate Current) nature it is very strange that <the hot wire, which provides a 120 VAC current (source)> and < the neutral wire. It provides the return path for the current provided by the hot wire.> as AC changes its direction with time regularly (sinusoidouslly) as the rate of 50/60Hz / second. So what do <xxx provides a 120 VAC current (source)> and <xxx return path for the current> mean? If we talk about DC sourced by a battery (batteries) the explanation seems more reasonable as DC has only one fixed direction all the time.
Let's be back to very basic things.
From: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html
Household Wiring
The standard U.S. household wiring design has two 120 volt "hot" wires and a neutral which is at ground potential. The two 120 volt wires are obtained by grounding the center tap of the transformer supplying the house so that when one hot wire is swinging positive with respect to ground, the other is swinging negative. This versatile design allows the use of either hot wire to supply the standard 120 volt household circuits. For higher power applications like clothes dryers, electric ranges, air conditioners, etc. , both hot wires can be used to produce a 240 volt circuit.
-----
Please read the above explanation and see carefully the transformer part.
Center Tap (Transformer) - Wiki
:
:
:
Common applications of center-tapped transformers
A full-wave rectifier using two diodes and a center tap transformer.
The above is the typical rectifier circuit by using center-tapped transformer.
We neglect the two diodes and get
Please regard 120V as 240V and 60V as 120V (actually any voltages will do for principal explanation as far as the ratio is correct. And then think about the only one circuit the (2nd winding) upper line (as hot wire) and the center tap wire (as the neutral wire) and neglect the lower line (hot line) shown in the above drawing of hyperphysics as well.
We then consider the resistor as the resistance value of the the whole system of the right hand side. This whole system may consist of several actual Resistors, Capacitors, Inductors, Diodes, Transistor, ICs, etc and consume Electrical Power (Energy) to do something for you. Now we consider the power consumed by this one system Resistor.
Power = I x V
You may know that in terms of Power AC or DC does not matter as
Next, or I would like to say "finally", you think about what is happening on the upper and center tap points of the secondary winding of the transformer. Again we cannot see them (can see by using oscilloscope but still this is not really happening there as the horizontal line of the oscilloscope screen is time) but guess it. It may not be the current "provided" (pushed out) at the point of upper point and not "return" (pulled in, pushed in) at the point of the center tap continuously as the current is AC = Alternate Current.
Still a big question remains - how actually and exactly Electrical Energy is transferred from a power station to a household in a big picture and how Energy (reached a household) is transferred from the inlet to the power consuming home appliance(s) in a small picture? Either in a big picture or small ;picture the basic behavior of Electric Energy may be the same.
sptt
