Circuit Materials

Cable

Armored Cable. Can be used indoors in dry locations, but it cannot be used outdoors or areas where metal armor will corrode. (see fig.1)

Fig. 1. Plastic sheathed cable (NMC), often called ROMEX, BX is an armored cable (AC) and should be used wherever there is a chance of physical damage. It is the most common type of electric cable, use in residential wiring application.

The plastic-sheathed cable is preferred, because it is more flexible and easier to pull and strip. It is more convenient when used in fishing the wires or cables.

Another kind of nonmetallic sheathed cable is a corrosion-resistant. It is called NMC. Used for any residential wiring application except the service entrance. It is installed in moist, damp, and corrosive locations. 

Nonmetallic cables (NM and NMC) are very convenient. But problems can and will arise if handled improperly or carelessness.

Common possible problems that may occur:

• If you bend nonmetallic cable too sharply, you can split the insulation of the individual wires and cause short circuits. 
• The insulation also can get worn through in spots if you pull the cable carelessly through holes.

To prevent this problems: 

• Just be careful when installing NM or NMC cables and make a good practice, take 5 mins, used to observe where the wire is going to run. This will reduce the possibility of complications.

Wire Sizes

Wire sizes are measured by gage numbers. It gets bigger as the wire diameter gets smaller. See Fig 2.

Fig. 2. The thicker the wire size, the smaller the gage number becomes.

When you think about wire, you think about ampacity, which is current or amperage capacity. 

In ordinary electric work, wire sizes run from size 000 ( biggest), to size 14 (smallest). For house wiring, a rule of thumb by many skilled electricians is never to use anything smaller than No. 12, which allow extra ampacity for future load.

Shown below is Table 1:  Rule of Thumb Wire Ampacity:

The aim, therefore, is to install wire that's thick enough for a safe installation, but not so thick that its capacity is wasted.

"The thicker the wire is, the more current it will carry without getting overheated".

Outlet Box

Outlet boxes may be constructed of aluminum, galvanized steel, or plastic. They are measured in cubic inch capacity to determine the number and sizes of wire allowed in each box.

Example in Fig. 3 shown below, a 4-in. octagon box is used for wiring spotlights.

Fig. 3. A 4-in. octagon box is convenient to use when installing ceiling fixtures. A 4-in. square box is often used in walls for mounting switches and receptacles.

Available also are 4-in. square boxes and "handy boxes," and many others. A handy box is so called because it has a nail-on adapter. See Fig. 4.

Fig. 4. A "handy box" with built-in, nail-on adapters is designed to enable the electrician to install the box quickly in awkward places.

Fixtures & Receptacles (in Boxes)

According to the National Electrical Code (NEC) (see Article 314 NEC 2011), only a limited number of conductors are allowed in a box. The rule is that the boxes shall be large enough in volume to provide free space for all the conductors enclosed in the box.
Table 2 lists some of the typical combinations permitted.

Table 2

A conductor that runs straight through a box counts as only one wire. Wires to fixtures are excluded from counts and the rest of the conductor are all counted as shown in Fig. 5.

Fig. 5. Counting conductors in the box, and following proven wiring rules, ensures that the installation will be permanently safe.

 Take note that a receptacle or switch count as one wire, as do any fixture studs.

Conduit

There are three (3) kinds of conduit, generally use. These are:

1. Rigid Metal Conduit (RMC)
2. EMT (Electric Metallic Tubing) or "Thin Wall"
3. IMC (Intermediate Metal Conduit)

Rigid Metal Conduit (RMC)

Definition (According to NEC Code-Article 344.2): A threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings. RMC is generally made of steel (ferrous) with protective coatings or aluminum (nonferrous). Special use types are red brass and stainless steel.

Electric Metallic Tubing (EMT)

NEC Code Article 358.2 Defines: An unthreaded thin-wall raceway of circular cross section designed for thphysical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed utilizing appropriate fittings. EMT is generally made of steel (ferous) with protective coatings or aluminum (nonferrous).

Intermediate Metallic Tubing (IMC)

NEC Code Article 342 states that: IMC is thinner-walled and lighter in weight than rigid metal conduit, and is satisfactory for uses in all locations where rigid metal conduit (RMC) is permitted to be used. Threaded fittings, couplings, connectors, and so on, are interchangeable between IMC and RMC. Threadless fittings for IMC are suitable only for the type of conduit indicated by the marking on the carton.

Article 342.2 defines: Intermediate Metal Conduit (IMC) - A steel threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings.

Conduit is easy to install in new work, since the walls are open. The conduit is installed to the framing works along with boxes.

The NEC permits only four (4) 90 degree bends in any conduit between two boxes. The bends are made with a conduit bender. Benders are also called conduit benders, persuaders, or hickeys. (See Fig. 6)

Fig. 6. Conduit must be carefully bent so there are no crimps or dents. Special tools, called "persuaders" or conduit benders, have to be used for this task.

How to determine what size of conduit to buy or used? 

The number of wires allowed to pass through the conduit depends on the size of wire and the type of insulation on the cable. 

The NEC allows only 40% of the conduit area to be filled.

Cutting, Splicing and Connecting Wires

There are two (2) ways to splice wires permanently:

1. Using a solder
2. Using wire nuts or other types of solderless connectors

See Illustration below:

 Fig. 7. There are two (2) ways to splice, both permanent. One method is solderless with pressure holding the wires together. The other method uses solder, which connects the wires electrically as well as mechanically.

How  to splice?
When making a solder splice, remove about 3 in. of insulation then cross the wires about an inch from the insulation and twist it neatly together. Thicker wires may require using a pair of pliers, not just fingers. After twisting, the wires will be heated and solder applied to the splice accordingly.
Solderless connection. A wire nut makes a a solderless connection permanent. Put the two ends of clean wire together and push them into the nut. Then screw the nut down tightly to the wire. Tightening the wire nut to the wires, a satisfactory connection is made.

When attaching a wire to a screw connection, always bend the end of the wire into a loop. Then attach the loop under the screw in the direction the screw tightens as in Fig.8. A variety of crimp-on connectors are also available for installing wires on screw terminals. The cutter-stripper tool can generally be used to crimp these connectors to the wires.

Fig. 8. A simple thing like putting a screw connection in the wrong direction can cause faulty connections.

Electric Service

The Service Panel

The typical panel shown in Fig. 1 is rated to handle 200A and it has 48 circuit positions.

Fig. 1. A typical 200 Amp panel has 48 circuit positions. This one has seventeen 120V breakers, eleven 240V double-pole breakers, and nine circuits spare.

On the panel, you can see that there is an index label pasted and numbered 1 through 48. It is a good practice to fill in the circuit description on the label. In that case, if you need to disconnect any circuit during troubleshooting or maintenance, you know where the breaker is located in the panel.

Each branch circuit has its own circuit breaker in the panel. To be exact, the "hot" wire at a potential of 120V, which is typically black, connects to the terminal alongside the breaker. The white wire in the cable connects to a neutral strip (bus) located inside the panel, as illustrated in Fig. 2.

Fig. 2. The service panel gets three wires from the electric company. Each circuit breaker feeds a hot wire to a branch circuit.

When you need 240V for a branch circuit, use three-wire cable. The third wire is usually red. The 240V breakers have two "hot" terminals, one for the black wire and the other for the red wire. White still goes to the neutral strip, along with all the other white wires from the other branch circuits.

In addition to the hot wires and the neutrals, you will also find a green or bare wire with most branch circuits. This wire is used solely for safety purposes; it does not carry any current. It is used to place the metal enclosures of electrical equipment at a true ground potential for the prevention of electrical shocks.

The primary function of the service panel is to disconnect automatically, by means of the breaker or fuse, any defective circuit that could draw too much current, such as the appliance in Fig. 3.

Fig. 3. Should a short circuit develop in one of the branches, a fuse blows or a circuit breaker trips for that branch circuit.

Between the electric meter and the branch circuits is found the main disconnect. Its current rating is the total sum of all the branch circuits. The main disconnect has the function of shutting off all power in case of a major or total breakdown in the wiring system.

The main disconnect gets the 3-wire input from the meter. Typically, the black wire of the cable connects to the left terminal and the red wire connects to the right terminal. The third wire, which is bare, attaches to the neutral strip in the box and it is grounded securely by connecting it to an approved ground, such as a cold-water pipe.

Electric Meters

The electric meter is supplied by the electric company and is plugged into a meter socket that the electrical contractor supplies and installs. The meter is sealed by the electric company. When there is meter trouble, the power company will handle it.

The meter socket is simply a connecting device that receives a 3-wire input from the entrance head. The black wire is attached on the left and the red wire on the right. Neutral goes right through unbroken, as shown in Fig. 4.

Fig. 4. The electric meter itself is supplied by the power company, but the electrical contractor is responsible for installing the meter socket.

The meter device is a very slow moving electric motor. It turns faster as more current flows, and slows down as current consumption is reduced.

The meter is simple to read. You can record each number from left to right. The meter is read periodically, usually once a month.

Entrance Head

The entrance head, or weatherhead, in Fig 5, is a connecting device for the service entrance conductors after they are spliced to the service drop from the electric company.

Fig. 5. The entrance (weatherhead) is a part of the service entrance. It connects between the service drop and the meter by cable or raceway.

The service entrance conductors extend from the end of the electric company service drop, through the entrance head, through the meter, and into the service panel, ending at the main disconnect.

When installing the entrance head, a great deal of thought is given to keeping water and weather out off the conduit.

The entrance cable from the weatherhead to the service drop must be at least 36 in. long. The black wire should be on the the left and the red wire on the right. The neutral is in the center of the head.

The weatherhead has to be above the top insulator of the incoming service drop. That way, water running down the service drop cannot enter the weatherhead.

Service Drop

The service drop is so called because the wires from the electric company usually take a downward drop from the electric pole to the weatherhead. 

The service drop belongs to the electric company and is installed by them. The National Electrical Code (NEC) recommends how and where a service drop is to be installed.

For example, service drops have to have a clearance of not less than 3 ft from the highest points of roofs under certain circumstances.

Service drops can be installed on the sides of buildings or to a mast holding the entrance head  as in Fig. 6.

Fig. 6. The service drop is designed to be safely installed above different kinds of areas. A mast-type riser is often required to achieve minimum mounting heights.

While most illustrations show the drop ending in three separate wires, the three wires can be wrapped together across the drop to give a neat appearance and to make the wires less exposed to weather damage. The resulting cable is called triplex.

The service entrance wires are attached to the service drop wires with strong, bolted connections. At the bottom of the drip loop, a tiny notch is sometimes made in the insulation. That way, when there is heavy rain, the drip loop cannot possibly develop a siphon effect and cause water to run upward into the weatherhead and conduit.

Service Grounding

You've probably heard the term ground, neutral, and common. The term "ground" means that the ground we live on is a reference potential for almost every electric circuit.

All conductors in electric cables have their insulation color coded. Black and red insulation is used on the "hot" wires, and white insulation is used on the neutral wire. The neutral is usually attached to ground at the service panel. By "ground" is meant the true earth ground.

The electrical code also requires that one current-carrying wire of the electrical system must make a good, permanent electrical connection to ground. This, of course, is the neutral or common wire.

Ground is at a potential of zero volts for every circuit.

Exposed metal in an electrical system that is correctly grounded is safe to touch.

Grounding must take place at the service entrance, as illustrated in Fig. 7. The neutral strip in the service panel must be grounded.

Fig. 7. The service-entrance neutral conductor must be grounded correctly to a true earth ground, usually a water pipe or a special grounding electrode.

There are two general methods of grounding the service entrance:

1. One method involves the use of a No.4 wire, safely hidden from mechanical injury, which is attached to a cold-water pipe in your plumbing system. (See Fig. 8.)
2. The second method of grounding, may be typical for a farm, where lightning strikes are more common and the ground has to function as a lightning arrester. (See Fig. 9). A grounding conductor is then attached to the rod with the correct ground clamp and run to the neutral overhead wire on the drip loop.

Fig. 8. In an urban area the ground must lead to the street side of the water meter and be protected carefully from any mechanical injury.

 Fig. 9. On a farm, due to its isolation and the greater possibility of lightning strikes, the ground system usually has separate grounding rods.

*To sum up, the electric service entrance consists of the circuits that handle the power company's entry into the home. It includes the entrance cables from the service drop splice, the weatherhead, the kilowatt-hour meter, the service entrance disconnect, and the grounding components.

  

Electricity - Explained

"What is Electricity?"

Electricity comprises those physical phenomena involving electric charges and their effects when at rest and when in motion. In short, it is the movement of electrons.

What are electrons?
An elementary particle which is the negatively charged constituent of ordinary matter. It is the lightest known particle or virtually weightless, but if they are in motion, they become an electric current. It is a particle which can be found in every substance.
Electrons have a single main characteristic. They have an electric charge, and all electrons have the same kind of charge. It is called a negative charge.
The electric charge around an electron acts something like a magnetic field. The behavior of positive and negative charges is very similar to the behavior of the two poles (north & south) of a magnet. All of these same negative charges do one thing: they repel each other.
In wiring conductors, billions of free electrons are safely in place in their fields. They are distributed evenly throughout the wire as shown in Fig.1.

Fig. 1. In every conductor, such as a copper wire, there are a large number of free electrons.


Direction of Electron Flow


As mentioned earlier, electrons are almost weightless, if you can get one to move, the repulsion of the like charges will make every free electron in the wire move. As illustrated in Fig.2, they will all move basically in the same direction.

Fig. 2. When the electrons are forced to move, they become a current flow and are able to perform work. No one electron moves from one end of a conductor to the other.

In order to do work, the electrons have to be in motion. Electrons do no work if they are motionless.
It doesn't matter whether the electrons move in one direction or in the other direction. They can start off in one direction, stop, reverse themselves, and vice versa. The important thing is to have them move when they are supposed to. Work is performed as long as the electrons move.
Common electron movement used in the United States and other similar countries, is the electricity that caused to flow through wires at a 60 Hz (cycles per second) frequency and 50 Hz for some other countries especially in Europe. This means the electrons flow first in one direction, then in the reverse direction, repeating this cycle 60 times or 50 times every second.


Electrical Pressure, or Voltage

Electrons can be forced to move by pushing more electrons into the wire, as in Fig 3. However, no electrons can get into the wire unless an equal number of electrons are pushed out the other end.
For instance, when you plug a lamp into a wall receptacle, electrons force their way into one wire. The electrons are moved through that wire, through the filament of the lamp, and out through the other wire.
If the filaments are broken, the electrons cannot move. The path is now open, apparently the electrons cannot travel in an incomplete circuit.
The force motivating electrons to "flow" in a wire or circuit is called voltage. Voltage is a specific measure or difference of potential between any two conductors of the circuit concerned. Common typical voltage range assigned to a circuit or system are 120/240V, 480Y/277V, 600V and according to the NEC Code, the actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.

Fig. 3. When voltage (electrical pressure) is applied to a wire, the loose electrons are packed under pressure. Note how many more electrons there are in this section of wire than there were in the previous diagrams.

Flow of Current

The amount of electric current that flows is measured in amperes (amps).
It doesn't matter which way the current flows, or if it turns around in midstream and flows in the reverse direction. The only thing that counts is the rate of flow of electrons that pass a cross section of wire, such as the section being monitored in Fig. 4.

Fig.4. The electric current flow or amperage which can be measured with an ammeter is the rate of electron flow that passes through a cross section of wire.

As the current flows, the resulting work consumes energy. The current tends to heat what ever it is moving through. Examples: If it is passing through a filament of lamp, the filament gets white hot and emits light; When it passes through the heating element of a toaster, the element gets red hot and transmits heat to the bread; Should current be passing through the field coils of a motor, a magnetic field is generated that makes the motor rotate, producing mechanical power.
The amount of current used varies accordingly as different appliances are turned on and off. This, you will pay the electric company for the amount of current flow you use from their wires or cables.


What is a Watt?

Watts are the unit of measurement for electrical power. Power is a measure of the instantaneous electrical work being done. Voltage times current equals watts. Therefore,

E = voltage;
I =current

then,

E x I = Power (P), in watts (W) or simply P = EI

Since a watt of power is so small, power is measured in kilowatts (KW), which are thousands of watts.

You do not, however, pay the electric company for power; you pay for energy. Energy is the amount of power used over a period of time. The common energy unit is the called the kilowatt-hour (kWh). That's the amount of energy used when a kilowatt of power is taken from the utility for 1 hour. In Fig.5 are shown a number of appliances that would use 1000W (1 kW) of power if they were all turned on at the same time.

Fig.5. If all these appliances were turned on, you would be using 100 watts of electricity. When 1000 watts of electricity is used for one hour, it is measured as a kilowatt-hour.

The wattage of an appliance is simply the amount of power needed to enable the appliance to function properly, and the kilowatt-hour reading from the electric meter lets you know how much energy you have to pay the electric company for.