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Log in with Facebook Log in with Google. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. Download Free PDF. The Complete Guide to Electrical Wiring. Angky Tri Aditya. A short summary of this paper. Download Download PDF. North, Suite , Minneapolis, MN First edition published pages cm by Cowles Creative Publishing, Inc. With the exception of quoting brief passages fully compliant with the National Electrical Code.

Full-color for the purposes of review, no part of this publication may be photography and step-by-step information covers all of the most reproduced without prior written permission from the Publisher. The information in this book is true and complete to the best of our Includes index. All recommendations are made without any guarantee ISBN paperback on the part of the author or Publisher, who also disclaims any liability 1.

Electric wiring, Interior--Amateurs' manuals. Dwellings-- incurred in connection with the use of this data or specific details. Maintenance and repair--Amateurs' manuals. Dwellings--Electric equipment--Amateurs' manuals. To find out more The techniques shown in this book are general techniques for various applications. In some instances, additional techniques not shown in this book may be required. The projects in this book vary widely as to skill levels required: some may not be appropriate for all do-it-yourselfers, and some may require professional help.

Consult your local building department for information on building permits, codes, and other laws as they apply to your project. Typically, most simple home wiring projects are unaffected by the changes to the NEC, which is updated every three years.

But according to top-notch home inspector Bruce Barker, who helped us update this book for its 6th edition, there are four code alterations that may impact homeowners and their DIY wiring projects soon. Most local governing authorities use the NEC as the basis for their set of codes, although it usually takes a few years before the changes are adopted. And local codes always supersede any national codes. Here are the changes most likely to affect your wiring project, based on the new edition of the NEC: 1.

The available neutral at switch boxes. Some switch wiring methods require that the white wire be used and labeled as a hot wire. A single pole switch at the end of the circuit a switch leg is one example. Three- way and four-way switches are other examples. New computer-controlled and timer switches need power to operate, which means that a neutral wire is required to complete the electrical circuit.

To allow easier installation of these new switches, the new NEC requires an available neutral wire in many switch boxes. In most cases, you will just cap the neutral wire and leave it, looking a bit lonely, in the switch box. You may need to substitute 3-wire cable where you formerly used 2-wire cable, or you may need to substitute 2 runs of 2-wire cable where you formerly used 3-wire cable.

Our new wiring diagrams will show you how to do this. When it goes into effect, this change will apply only to new construction and expanded circuits. AFCI protection for most circuits. The new NEC expands this requirement to include most 15 and 20 amp, volt, receptacle and lighting circuits. Exceptions include the kitchen and bathroom receptacle circuits and the garage and exterior receptacle circuits.

AFCI circuit breakers are required in most cases. Adding an AFCI device may not be as easy as installing it. Some AFCI devices may not be compatible with shared neutral multi-wire branch circuits. Some AFCI devices may not be compatible with dimmers, especially solid-state dimmers. You may want to have an electrician help you when you install AFCI devices. Garage receptacles may not feed other outlets. You may no longer tie into a receptacle in your garage to power anything outside of the garage, such as an outdoor security light.

Also, you must provide a receptacle for every parking spot in the garage. The most essential quality to appreciate about electricity is that the typical amounts that flow through the wires in your home can be fatal if you contact it directly. Sources estimate that up to 1, people are electrocuted accidentally in the U.

In addition, as many as die in fires from electrical causes. This chapter explains the fundamental principles behind the electrical circuits that run through our homes.

The beginner should consider it mandatory reading. Even if you have a good grasp of electrical principles, take some time to review the material. A refresher course is always useful. Electrical current flows in wires in much the same way that water flows Water flows under pressure inside pipes.

In plumbing, water first flows through the pressurized water supply system. In electricity, current first flows along hot wires. Current flowing Water supply pipe along hot wires also is pressurized. Electrical pressure is called voltage. Large supply pipes can carry a greater volume Drain pipe of water than small pipes.

Likewise, large electrical wires carry more current than small wires. This electrical current-carrying capacity of wires is called ampacity. Water is made available for use through the faucets, spigots, and showerheads in a home. Electricity is made available through receptacles, Water returns under no pressure switches, and fixtures.

Water finally leaves the home through a drain system, which is not pressurized. Similarly, electrical Water and electricity both flow. The main difference is that current flows back through neutral wires. Power plants are located in all parts of electricity to large volt appliances such as clothes the country and generate electricity with generators dryers or electric water heaters.

Electricity that increase voltage to half a million volts or more. The travels through high-voltage transmission wires to service panel also contains fuses or circuit breakers communities that can be hundreds of miles from the that shut off power to the individual circuits in power plants.

Certain substations then reduce the voltage for distribution high-wattage appliances, such as microwave ovens, are along street wires. On utility power poles, smaller usually plugged into their own individual circuits to transformers further reduce the voltage to ordinary prevent overloads. Voltage ratings determined by power companies Wires carrying electricity to a house either run and manufacturers have changed over the years.

Most homes built after new devices connected to older wiring. For making have three wires running to the service head: two electrical calculations, use a rating of volts or power wires, each carrying volts, and a grounded volts for your circuits. Electricity from the two volt wires Power plants supply electricity to Substations are located near the Electrical transformers reduce thousands of homes and businesses.

A typical the high-voltage electricity that flows Step-up transformers increase the substation takes electricity from through wires along neighborhood voltage produced at the plant.

A utility pole transformer—or and reduces it for distribution along ground transformer—reduces voltage street wires. The mast is It is usually attached to the side of the house and connects supplied with three wires, two of which the insulated wires to the service mast. The electric meter belongs to your each carry volts and originate at the nearest transformer. If you suspect the meter is not In some areas electricity enters from below ground as a functioning properly, contact the power company.

Current flows back to neutral at service mast Surges in current flow to grounding rod A grounding wire connects the electrical system to the earth Light fixtures attach directly to a household electrical through a metal grounding rod driven next to the house. They are usually controlled with wall switches. The two common types of light fixtures are incandescent and fluorescent.

According to box, distributes power to individual circuits. Fuses or circuit the National Electrical Code, all wire splices and connections breakers protect each circuit from short circuits and overloads. Switches control electricity passing through hot circuit Receptacles, sometimes called outlets, provide plug-in wires. Switches can be wired to control light fixtures, ceiling access to electricity.

A volt, amp receptacle with a fans, appliances, and receptacles. Most receptacles have two plug-in locations and are called duplex receptacles. Usually covered with white or light gray insulation. Also called the grounded wire. Armored cable: An assembly of insulated wires enclosed in a flexible, interlocked metallic armor.

Non-metallic sheathed cable: NM cable consists of two or more insulated conductors and, in most cases, a bare Box: A device used to contain wiring connections.

BX: A brand name for an early type of armored cable that Outlet: A place where electricity is taken for use. A is no longer made. The current term is armored cable.

A box for a ceiling Cable: Two or more wires that are grouped together and fan is another type of outlet. Overload: A demand for more current than the circuit Circuit: A continuous loop of electrical current flowing wires or electrical device was designed to carry. This along wires. Circuit breaker: A safety device that interrupts an Pigtail: A short wire used to connect two or more wires to electrical circuit in the event of an overload or short circuit.

Conductor: Any material that allows electrical Polarized receptacle: A receptacle designed to keep current to flow through it. Copper wire is an especially hot current flowing along black or red wires and neutral good conductor. Conduit: A metal or plastic pipe used to protect wires. Power: The work performed by electricity for a period of time.

Use of power makes heat, motion, or light. Continuity: An uninterrupted electrical pathway through a circuit or electrical fixture. Receptacle: A device that provides plug-in access to electricity. Current: The flow of electricity along a conductor. Romex: A brand name of plastic-sheathed electrical Duplex receptacle: A receptacle that provides cable that is commonly used for indoor wiring.

Commonly connections for two plugs. Flexible metal conduit FMC : Hollow, coiled steel or Screw terminal: A place where a wire connects to a aluminum tubing that may be filled with wires similar to receptacle, switch, or fixture. Armored Cable, but AC is pre-wired.

Service panel: A metal box usually near the site where Fuse: A safety device, usually found in older homes, electricity enters the house. In the service panel, electrical that interrupts electrical circuits during an overload or current is split into individual circuits. In residences, the service short circuit. Greenfield: A brand name for an early type of flexible Short circuit: An accidental and improper contact metal conduit. The current term is flexible metal conduit.

Grounded wire: See neutral wire. Switch: A device that controls electricity passing Grounding wire: A wire used in an electrical circuit to through hot circuit wires.

Used to turn lights and conduct current to the service panel in the event of a ground appliances on and off. The grounding wire often is a bare copper wire. In an electrical an organization that tests electrical devices and circuit, the hot wire usually is covered with black or manufactured products for safety. Voltage or volts : A measurement of electricity in terms Insulator: Any material, such as plastic or rubber, that of pressure.

Insulating materials Wattage or watt : A measurement of electrical power protect wires and cables. Watts can be calculated Junction box: See box. Meter: A device used to measure the amount of electrical Wire connector: A device used to connect two or more power being used. Also called a wire nut. Chandelier Wall switch Receptacles Switch loop Separate volt circuit for microwave oven oven. GFCI receptacles Separate volt circuit for water heater heater.

Electric meter measures the amount the amount of electrical of electricity power consumed and displays Service panel distributes the measurement inside electrical power into circuits circuits. Bonding wire to metal grounding rod rod.

Bonding wire to metal water pipe pipe. Jumper wire is used to bypass the water meter and ensures an uninterrupted grounding bonding pathway pathway. Household circuits carry electricity from the main service panel, throughout the house, and Service back to the main service panel. Several switches, panel receptacles, light fixtures, or appliances may be connected to a single circuit.

Current enters a circuit loop on hot wires and Main circuit returns along neutral wires. These wires are color Main circuit hot wires coded for easy identification. Hot wires are black neutral wire Circuit breakers or red, and neutral wires are white or light gray. For safety, all modern circuits include a bare copper or green insulated grounding wire. The grounding wire conducts current in the event of a ground fault see page and helps reduce the chance of severe electrical shock.

The service panel also has a bonding wire connected to a metal water pipe and a grounding wire connected to a metal grounding rod, buried underground, or to another type of grounding electrode. If a circuit carries too much current, it can overload. A fuse or a circuit breaker protects each circuit in case of overloads. Current returns to the service panel along a neutral circuit wire. Current then leaves the house on a large neutral service wire that returns it to the utility transformer.

Contrary to popular belief, electricity will take all available return paths to water and gas pipes are the most common examples. A metal water and gas pipe could become energized by coming in contact with a damaged electrical wire. In a Metal gas pipe could become energized by a ground household wiring system, this return path is provided fault in a gas appliance such as a furnace.

A service panel. From the service panel, current returns person could receive a fatal shock if he or she touches along the uninsulated neutral service wire to a power energized metal that is improperly bonded, because pole transformer. Bonding is also a fire safety system that in this and other books about electricity.

These terms reduces the chance of electrical fires. Grounding also metal conduit, in a continuous low-resistance path provides a secondary return path for electricity in case back to the main service panel.

If this metal becomes there is a problem in the normal return path. The dead electrode. The most common grounding electrode circuit alerts people to a problem. Metal ufer ground. Current Service panel Black hot wire returns to Grounding wire transformer White neutral wire Grounding screw Grounding wire Loose hot wire Grounding wire to Grounding wire to grounding rods grounding rods 8 ft.

Small amount 8 ft. The grounding wire and bonded metal white neutral wire. Most current in the bonding and ground system flows back to the transformer; some may trickle out through the copper that leads to the grounding node.

By plugging a receptacles that accepted polarized plugs. The three-prong plug into a grounded three-slot receptacle, two-slot polarized plug and receptacle was designed to people are protected from ground faults that occur in keep hot current flowing along black or red wires and appliances, tools, or other electric devices.

Use a receptacle adapter to plug three-prong The metal jacket around armored cable and plugs into two-slot receptacles, but use it only if the flexible metal conduit, widely installed in homes receptacle connects to a grounding wire or grounded during the s, provided a bonding path. When electrical box. Note, however, mounting screw. The mounting screw connects the that deterioration of this older cable may decrease its adapter to the grounded metal electrical box. Modern NM nonmetallic cable, Armored cable is sold pre-installed in Polarized receptacles have a long slot found in most wiring systems installed a flexible metal housing.

It contains a and a short slot. Used with a polarized after , contains a bare copper wire green insulated ground wire along with plug, the polarized receptacle keeps that provides bonding for receptacle black and white conductors. Flexible electrical current directed for safety. Tamper resistent three-slot A receptacle adapter allows Double-insulated tools have receptacles are required by code three-prong plugs to be inserted into non-conductive plastic bodies to for new homes.

They are usually two-slot receptacles. The adapter should prevent shocks caused by ground connected to a standard two-wire cable only be used with receptacles mounted faults. Because of these features, with ground. As with any tool purchase, The materials used for electrical wiring have changed dramatically in the last 20 years, making it much easier for homeowners to do their invest in quality products when you buy tools for own electrical work.

The following pages show electrical work. Keep your tools clean, and sharpen or how to work with the following components for replace any cutting tools that have dull edges. Electrical tapes in a variety of colors are used for cavities and for pulling wires through conduit. Products marking wires and for attaching cables to a fish tape. Although most household electrical repairs are simple and straightforward, the circuit breaker that controls the circuit you are servicing.

Then check to make sure the power is off by testing for power with a voltage tester. Tip: Test a live always use caution and good judgment when working circuit with the voltage tester to verify that it is working with electrical wiring or devices. Common sense can before you rely on it. Restore power only when the prevent accidents. The basic rule of electrical safety is: Always turn Follow the safety tips shown on these pages.

At Never attempt an electrical project beyond your skill the main service panel, remove the fuse or shut off or confidence level. Shut power OFF at the main service panel or the main Create a circuit index and affix it to the inside of the door to fuse box before beginning any work. Update it as needed. These fixture with a voltage tester. On damp floors, stand on a rubber mat or dry household repairs near the service mast. Extension cords are for temporary use only.

Cords must be Breakers and fuses must be compatible with the panel rated for the intended usage. Never alter the prongs of a plug to fit a receptacle.

If Do not penetrate walls or ceilings without first shutting off possible, install a new grounded receptacle. Selecting the appropriate size and type and handling it correctly is absolutely necessary to a successful wiring project that will pass inspection. Copper wire is the primary conductor of electricity in any home. The electricity itself travels on the outer surfaces of the wire, so insulation is normally added to the wires to protect against shock and fires.

The insulated wires are frequently grouped together and bound up in rugged plastic sheathing according to gauge and function. Multiple wires housed in shared sheathing form a cable. In some cases, the wires are grouped in metal or plastic tubes known as conduit. Conduit also known as raceway is used primarily in situations where the cables or wires are exposed, such as open garage walls. This chapter introduces some of the many varieties of wire, cable, and conduit used in home construction and explains which types to use where.

It also will demonstrate the essential skills used to run new cable, install conduit, strip sheathing, make wire connections, and more. Solid copper wires are the best conductors of electricity and are In most wiring systems installed after , the wires and cables are insulated with plastic vinyl.

This type of insulation is very durable and can last as long the most widely used. Aluminum and copper-covered as the house itself. Before , wires and cables were insulated with A group of two or more wires enclosed in a metal, rubber. Rubber insulation has a life expectancy of about rubber, or plastic sheath is called a cable see photo, 25 years. Old insulation that is cracked or damaged opposite page. The sheath protects the wires from can be reinforced temporarily by wrapping the wire damage.

Conduit also protects wires, but it is not with plastic electrical tape. However, old wiring with considered a cable. An exception is a bare copper Wires must be large enough for the amperage grounding wire, which does not need an insulation rating of the circuit see chart, below right.

A wire cover. The insulation is color coded see chart, below that is too small can become dangerously hot. Wire left to identify the wire as a hot wire, a neutral wire, sizes are categorized according to the American Wire or a grounding wire.

New cable sheathing is also Gauge AWG system. To check the size of a wire, use color coded to indicate the size of the wires inside. Wire sizes shown actual size are categorized by the American In some circuit installations, the white wire serves as a hot wire Wire Gauge system. The larger the wire size, the smaller the AWG that carries voltage. If so, this white wire may be labeled with number. The ampacities in this table are for copper wires in NM black tape or paint to identify it as a hot wire.

The ampacity for the same wire in conduit is usually more. The ampacity for aluminum wire is less. Wires are covered with a layer of rubberized cloth, cloth fabric, but have butadditional no have no additional protection. Metal clad cable MC and armored cable AC have been around since the s. Early versions had no grounding function, but existed solely to protect the wires that were threaded into it. Later armored cable products either had ground wire twisted in with the flexible metal cover or relied on the metal cover itself for connecting to ground.

Modern MC contains an insulated ground wire along with the conductors. Metal conduit was installed during the middle of the 20th century as a way to protect hot and neutral conductors.

The conduit itself often was employed for connecting to ground. Early NM nonmetallic cable was used from until It features a rubberized fabric sheathing that protects individual wires. NM cable greatly simplified installations because separate wires no longer had to be pulled by hand through a conduit or armored cable.

Early NM cable had no grounding wire. NM cable nonmetallic was developed cable was around developed around The UF underground feeder cable has wires embedded in a solid-core plastic vinyl sheathing and includes a bare copper grounding wire. It is designed for installations in damp conditions, such as buried circuits. It is available in lengths up to 25 ft. Or you can buy bulk cable B in any length. A NM nonmetallic sheathed cable should be used for most indoor wiring projects in dry locations.

NM cable is sold in boxed rolls that contain from 25 to ft. B of cable. Each wire, purchased individually, is covered with a color-coded thermoplastic insulating jacket. It can also be used or amp appliances that require 8-gauge for kitchen ranges and other amp or amp or larger wire. It is similar to NM cable, but appliances that require 8-gauge or larger wire. Large-appliance conducting wire is made from fine-stranded cable is available in both 2-wire and copper wires.

SE cable is available in both 3-wire types. Cat 5 Category 5 cable is used mostly for 2-wire and 3-wire types. The cable contains four pairs of twisted copper wire with color-coded insulation. UF cable underground is used for feeder wiringcable in damp is used locations, for wiring in damp such as in locations, an outdoorsuch circuit.

Your phone company may recommend thatwires the protects inside. NM cable is allowed. Eight-wire cable has extra wires that are left unattached. These extra wires allow for future expansion of the system. The bare grounding wire is not counted. For example, raceway installations. Code two insulated gauge wires, plus a bare copper grounding requires certain letter combinations for certain applications. H stands for heat wires plus a grounding wire. Wire coded with an Laboratories UL.

N is impervious to damage from oil or gas. Minimum: two Minimum: two Minimum: two gauge wires gauge wires gauge wires Maximum: four gauge Maximum: four or three gauge wires gauge wires Maximum: two gauge wires Use wire connectors rated for the wires you are connecting.

Wire connectors are color-coded by size, but the coding scheme varies according to manufacturer. The wire connectors shown above come from one major manufacturer. To ensure safe connections, each connector is rated for both minimum and maximum wire capacity.

These connectors can be used to connect both conducting wires and grounding wires. Green wire connectors are used only for grounding wires. Ampacity varies by the size of the wires. When installing gauge 20 amps 1, watts volts a new circuit, choose wire with 3, watts volts an ampacity rating matching the gauge 30 amps 2, watts volts circuit size.

For dedicated appliance watts volts circuits, check the wattage rating of the appliance and make sure it does 8-gauge 40 amps 7, watts volts not exceed the maximum wattage load of the circuit.

The ampacities in 6-gauge 55 amps 10, watts volts this table are for copper wires in NM cable. Slide the cable ripper hand, and pull the cable ripper toward and the paper wrapping from the onto the cable, and squeeze tool firmly the end of the cable to cut open the individual wires. Choose the jaws of a combination tool. Leave a minimum opening that matches the gauge of of 3" of wire running past the edge of the wire, and take care not to nick or the box. Choose the stripper opening that the hole of the correct gauge in a pair of Tighten the screw firmly.

Insulation matches the gauge of the wire, and then wire strippers. The wire should have no should just touch head of screw.

Never clamp the wire in the tool. Pull the wire scratches or nicks. Instead, use a pigtail wire see page Choose Push-in connectors are a relatively new product staples sized to match the cables. These connectors are perfect attaching telephone cables. Grasp the wires to Twist a wire connector over the ends of the wires.

The ends sure the connector is the right size see page Hand-twist of the wires should be flush and they should be parallel and the connector as far onto the wires as you can. There should touching. Rotate the pliers clockwise two or three turns to be no bare wire exposed beneath the collar of the connector.

By code, you cannot bind the wire joint with tape only, but joined, and insert each wire into a push-in connector. Gently it can be used as insurance. Few professional electricians use tug on each wire to make sure it is secure.

Note: Pigtailing is done mainly to avoid connecting multiple wires to one terminal, which is a code violation.

Fold the wires neatly and press the fitting one end of the wire to the grounding screw before you attach into the box. Check with your building inspector before using NM cable. Some areas, such as the masonry walls with dirt on the other side. Cut and Chicago area, do not allow NM cable. Refer to your wiring plan to make sure each length of cable is correct for the circuit size and configuration.

Cable runs are difficult to measure exactly, so leave plenty of extra wire when cutting each length. Cable splices inside walls are not allowed by code. When inserting cables into a circuit breaker panel, make sure the power is shut off. After all cables are installed and all the ground wires spliced, call your electrical inspector to arrange for the rough-in inspection.

Prevent kinks by Hammer Wire connectors straightening the cable before pulling it through the studs. Use Fish tape Eye and ear protection plastic grommets to protect cables on steel studs inset.

Joists can be notched only in the end third of the overall span; never in the middle third of the joist. Different rules apply to wood I-joists, metal-plate-connected trusses, engineered beams, and beams assembled from lumber. In general, you may not drill and notch trusses and assembled beams. Manufacturers of I-joists and engineered beams have limits about the size and location of holes.

This Where cables will turn corners step 6, page 36 , drill is done easily with a right-angle drill, available at rental centers. Insert a cable clamp into the to enter the circuit breaker panel. Clip away the excess knockout, and secure it with a locknut.

Insert the cable through sheathing. Tighten the mounting screws on the clamp so the cable is gripped securely but not so tightly that the sheathing is crushed. Retrieve the cable through the staples work well where two or more cables must be anchored other hole using needlenose pliers inset. Run the cable to the first electrical box. Where the cable runs along the sides of framing members, anchor it with cable staples no more than 4 ft.

Hold the cable taut devices. Insert the cable through the knockout in the box. Take care not to nick the copper. Mark the floor grounding clip attached to the frame shown above or a green so the cable will be easy to find after the walls are finished. In boxes with fixture, join grounding wires together complex wiring configurations, also tag the individual wires to make final hookups with a wire connector.

If the box has easier. After all cables are installed, your rough-in work is ready to be reviewed by the internal clamps, tighten the clamps over electrical inspector. Drill From the unfinished space below the the location of the wall above. Choose a a 1" hole down through the top plate wall, use a piece of stiff wire with a location for the new cable that does not and into the stud cavity using a drill hook on one end to retrieve the fish interfere with existing utilities.

So you can see that the three friends, volt potential difference , resistance and current are best of friends. And just like friends, if you get two together, they will talk about the third friend. Similarly, by rearranging the Ohms Law equation, if you know two of the values, you can find out what the third one is. It is time to use the international abbreviations in the equations. This bizarre abbreviation has to do with history, where current used to represented in the French language.

Just remember one, and you can work out the rest when needed. The unit of resistance is named after him. Let us imagine that you have attached electrocardiogram ECG leads to your patient.

You then plug the ECG lead plug to its socket in the monitor. Unfortunately, as you are doing this, a piece of dirt gets into the plug. This makes the yellow wire have a poor contact with its counter part, increasing its resistance.

According to Ohms Law, the high resistance affects the voltage and current in the wire, disturbing the ECG tracing. The plug is unplugged and the dirt removed. Now the contact is good and the resistance is now low.

The electrons i. The direction of the current will change if the negative and positive poles of the source are exchanged. Let me try and make things clearer for you. To make the diagrams a little less crowded, I have simplifying them a bit. The potential difference source is represented with a minus and plus sign. The green arrow will show the direction of current.

Remember, current always flows from negative to positive. I will now describe to you the difference between DC and AC. Let us start with DC. Below is a series of images showing a circuit with a DC power source. The repeated images show you what happens over a time period. You will notice that over time, that the current has NOT changed direction green arrow remains in the same direction. This is the fundamental property of DC: the current does not change direction. AC is quite weird when compared to DC current.

In AC, the negative pole and positive pole of the source exchange themselves repeatedly. Since current travels from negative to positive, this means that the current also changes direction repeatedly. The series of images below show AC over time. The positive pole and negative pole keep alternating. In response to this, the direction of current also keeps changing repeatedly. This repeated alternating of current direction happens quite fast.

In many countries , it happens 50 or 60 times a second i. The animation below may help you to appreciate how rapid this is. The negative and positive poles alternate 50 times second. If you suffer from photosensitive epilepsy, please skip this animation.

You may wonder why someone would produce a weird current in the form of AC. There are good engineering reasons why we have AC, and this will be discussed later on. For now, we will continue our discussion about the way AC behaves. An oscilloscope has a screen that shows voltage changes over a time. The vertical axis represents voltage and the horizontal axis represents time. This helps us to visualise how current behaves over time, and will be very useful when we continue our discussion on AC and DC.

It measures the potential difference of the heart over time. Looks familiar? Below is a simplified oscilloscope. Right now, nothing is connected to the oscilloscope probes black and red probes and therefore the the tracing blue line remains on the baseline. Let us connect the oscilloscope to a DC source. The oscilloscope shows a straight line reading blue line above the baseline broken line. Oscilloscopes show change in direction of current flow by the trace crossing the baseline.

Let us reverse the plus and minus poles of the source i. You will see that the trace crosses the baseline from the top to the bottom. Let us change the polarity again, so it is back to how it was before. Again you will that the oscilloscope shows this change by making the tracing cross the baseline, in this case from the bottom to the top.

We first connect it to a DC source such as a battery. You will get a steady tracing above the baseline. Since with DC, the direction of current flow does not change, the tracing does not cross the baseline.

Now let us examine AC with the oscilloscope. You know that, unlike DC, the polarity of AC keeps changing, so you would expect to see something like this. However, the above square waveform is NOT what you see.

Instead you will see a waveform that has much more graceful curves, as shown on the oscilloscope on the right below. The reason why you see the graceful curves instead of the sudden square changes is because the polarity in AC does NOT change suddenly as shown below. The potential first starts to decrease and eventually becomes zero.

Then the polarity gets reversed and potential difference starts to rise till it reaches the maximum. The changes in polarity continue in this fashion. This is the waveform that you often see in text books. The above transition will be shown in a step by step manner. As each step is shown, you will see the AC wave form in the oscilloscope. You would have noticed that AC has periods where there is zero potential difference. During these times the current flow is zero.

Normally one does not notice these zero periods because they happen so fast. However, sometimes you can see these off periods in fluorescent lights tube lights. The off periods may make the light flicker faster than what is shown below, the computer animation is not fast enough. If you look around you will discover that your world is full of symbols.

When you are bored have a look around your operating room and you will find plenty of hidden symbols. Typically they will be found on electrical equipment. Look where monitoring leads and power leads connect. The electrical current that comes out of the wall sockets in homes and hospitals is mostly AC. Let us see how a transformer works. The transformer uses two very important properties in the world of electricity.

The first phenomenon used in transformers is that when a wire carries an electric current, it generates a magnetic field. In the example below, the wire coil is carrying direct current DC. The magnetic field is shown as a blue arc. Below, we demonstrate a wire coil carrying alternating current AC.

In DC the field is non changing, whereas in AC the field is changing all the time. Now let us discuss the second electrical phenomenon that makes transformers work. Electromagnetic induction refers to a phenomenon where if a wire or coil of wire as in our example is exposed to a CHANGING magnetic field, a current will be induced in the wire. In the example below, the changing i. It is important that the magnetic field is changing.

A non changing magnetic field as shown below will NOT induce a current in the coil. Now we can explain how the transformer works. The input AC goes into the primary coil pink. This produces a changing magnetic field blue arc with arrows. The changing magnetic field induces a current in the secondary coil green and in this way, electric energy is transferred from the primary coil to the secondary coil. At this point you can see that a transformer works only with AC, because it needs a changing magnetic field to transfer energy across it.