Questions 26-28 Flashcards
- Why is nonmetallic-sheathed cable popular in residential wiring?
Nonmetallic-sheathed cable is very popular in residential wiring because it is inexpensive and easy to install.
- What do the two numbers marked on nonmetallic-sheathed cable indicate?
The numbers provide information about the size of the wire and the number of conductors in the cable.
- Differentiate between type NM and type NMC cable.
Type NM cable is a nonmetallic-sheathed cable that has conductors within a nonmetallic jacket and is typically used for dry interior wiring. Type NMC cable is a nonmetallic-sheathed cable that has the conductors enclosed within a corrosion resistant, nonmetallic jacket.
- How is non-metallic -sheathed cable prepared?
Typically the cable must be cut to length, have the outer jacket removed to a distance from the end, and have a specified amount of insulation removed from the individual conductors.
- What does rough-in mean in regard to electrical installations?
Rough-in is the placement of electrical boxes and wires before wall coverings and ceilings are installed.
- Define receptacle box.
An electrical device designed to house electrical components and protect wiring connections.
- Where and how are receptacle boxes for NM cable installed?
Receptacle boxes and junction boxes must be installed at every point in the electrical system where NM cable is spliced or terminated. Receptacle boxes are installed so that every point in the system is accessible for future repairs or additions. Boxes must be completely covered to the point that a box becomes inaccessible.
- What are uses of the different types of receptacle boxes used in residential wiring?
Octagonal boxes are typically used in ceilings for lighting fixtures. Square and rectangular boxes are used for switches and receptacles. Any of the three are used for junction boxes.
- Define knockout.
A knockout is a round indentation punched into the metal of a box and held in place by unpunched narrow strips of metal.
- Why is cable stripped before being installed in a box?
Stripping the wire before installing the wire into a box saves time later when outlets and switches are being installed.
- Explain two methods of routing cables through solid corners.
Cables are routed through solid corners by using various methods. One method is to drill holes from each side at an angle to accommodate a cable run. Drilling holes from each side will save wire but may be time-consuming if the holes do not line up properly. Another method is to notch the corner studs, using steel plates for protection.
- At what intervals must NM and NMC cable be supported or secured?
NM and NMC cable must be supported or secured (stapled) every 4 ½ of cable run and within 12” of a box.
- Compare the three methods of residential grounding.
- Component grounding – is a grounding method where the ground wire is attached directly to an electrical component such as a receptacle. Component grounding requires that the ground wire be attached before the electrical component is permanently mounted.
b. Pigtail grounding – is a grounding method where two ground wires are used to connect an electrical device to a ground screw in the box and then to system ground. The box ground ire is secured to a threaded hole in the bottom of the box. Once secured, the cable ground wire is pigtailed to the box ground wire.
c. Clip grounding is a grounding method where a ground clip is slipped over the ground wire from the electrical device. The ground wire and ground clip are secured with pressure using a screwdriver.
- How are cables secured to outlet boxes?
Cables are secured to outlet boxes by clamps. The three types of clamps typically available for nonmetallic cables are saddle, straight, and cable connectors.
- Why would metallic-sheathed cable be used rather than nonmetallic-sheathed cable?
Metallic sheathed cable is often used instead of nonmetallic cable because it protect wires with it’s metal protective covering.
- Define bonding wire.
A bonding wire is an uninsulated conductor in armored cable that is used for grounding. The bonding wire is in contact with the flexible metal outer jacket to assure proper conducting (ground) path along the entire length of an armored cable.
- Identify the applications of the three types of armored cable the NEC recognizes for residential work.
The NEC recognizes three types of armored cable for residential work: AC, ACT, and ACL. AC and ACT armored cables are used in dry locations. Both AC and ACT may be finished through the air voids of masonry walls when the walls are not exposed to excessive moisture. Both AC and ACT may be used for under-plaster electrical extensions. ACT armored cable is used for either exposed work or concealed work. ACL armored cable is embedded in concrete or masonry, run underground, or used where gasoline or oil is present. ACL armored cable is lead-covered to provide additional protection for masonry and underground applications.
- Describe the method used to cut through the metal jacket of armored cable.
The first step is to cut through the outer armor (one of the convolutions) at a 45 degree angle about 6” to 8” from an end. To prevent damage to the insulation of conductors, care must be taken not to cut too deeply into the jacket of the cable. When the armored cable is cut, the cable is separated by twisting the two sections apart. The armored cable must be carefully flexed until the cable breaks. Twisting the cable can open the convolutions enough so that tin snips or cable cutters can be inserted.
- What is the purpose of an anti-short bushing?
An anti-short bushing is a plastic or heavy fiber paper device used to protect conductors of armored cable. The bushing covers the sharp edges at the ends of the armor to reduce the possibility of damage to conductor insulation.
- How is armored cable roughed-in into studded walls?
When roughing-in armored cable into studded walls, the cable must be pulled into position first and then cut to length. Pulling the armored cable into position then cutting length, reduces waste.
- What is the minimum bend radius used to prevent breaking armored cable?
The minimum bend radius used to prevent breaking armored cable is 90 degrees. At least five times the diameter of the wire.
- What is a conduit?
Conduit is a rugged protective tube typically metal, through which insulated conductors are pulled.
- List and define the three most common types of conduit.
Electrical metallic tubbing, ridged metal conduit, and flexible metal conduit are primarily used in residential. Electrical metallic tubbing is a light-glued electrical pipe often referred to as thin-wall conduit. Rigid metal conduit is a heavy-duty pipe that is threaded on the ends much like standard plumbing pipe. Flexible metal conduit is a conduit that has no wires and can be bent by hand. The conductor’s wires are not installed until the system is complete.
- What is a deburring?
It is the process of removing the rough edges off of conduit. It is called deburring, and is accomplished with a conduit deburring tool designed for this purpose.
- How is a 45 degree bend made in conduit?
To create a 45 degree bend, a hand bender is placed on EMT conduit. The handle of the bender is raised until the handle is in the vertical position. The handle is pulled until the angle required 45 degrees is completed.
- Define offset.
An offset is a compound bend in conduit used to bypass many types of obstructions.
- Describe the different types of conduit connectors.
A compression connector is a box fitting that firmly secures conduit to a box by utilizing a nut that compresses a tapered metal ring (ferrule) into the conduit. As the compression nut is tightened, the nut forces the ferrule into the conduit, locking the conduit in position. An indenter connector is a box fitting that secures conduit to a box with the use of a special conduit to a box with the use of a special indenting tool. Lastly a set screw connector is a box fitting that relies on the pressure of a screw against the conduit in place. Set screw connectors are also reusable.
- How is conduit joined together?
Conduit couplings are used to join conduit together.
- How is rigid metal conduit used in residential construction?
Typically for residences ridged metal conduit is only used for overhead service risers and for underground services.
- Define fishing.
Fishing is the term used for the process of pulling wires through conduit. The fish tape is extended and pushed through the conduit until the tape reaches an opening. At the opening the wires being installed are firmly secured to the fish tape. The fish tape is retrieved by pulling the tape out of the conduit with wires attached.
- What is a service entrance?
A service entrance is the link between a residence and the power company. Service entrances provide all the equipment necessary to obtain electricity and distribute it throughout a residence.
- List three tips for determining the placement of a service entrance.
- Keep the service wires as short as possible.
- Locate the service panel as close to the kitchen as possible to prevent costly wire runs to major appliances.
- Do not place the meter socket on the outside of a bedroom wall.
- How are the residential service entrances typically rated?
Service entrances for single family dwellings require a minimum 100 A capability. For larger residences and structures using electric heat, a 200 A or larger service entrance can be required.
- List the different types of service entrances.
Service entrances may be overhead riser, lateral (conduit), lateral (cabinet), and mobile home service entrances.
- What are the benefits of using lateral service entrances as opposed to overhead riser service entrances?
A lateral service entrance (conduit) has all service wires buried underground, creating a condition where the wires are subjected to less damage from the environment and allowing unsightly poles and service wires to be removed from streets and alleys.
- Describe how to secure service equipment.
Meter sockets and service panels must be firmly secured before any wires (cables) are pulled or conduit attached.
When service equipment is mounted on wood, wood screws or lag bolts are used to hold the equipment in place. When service equipment is mounted to masonry, drills and special bolts with anchors are used. Plastic anchors support a considerable amount of weight when properly installed.
- What colors of wires are used for electrical wiring in a residence and what is indicated by each color?
Red, black, and white wires for the service panel enter the residence through a service head. The red and black wires represent the hot or live wires, and the white wire represents the neutral.
- What is the purpose of bus bars?
Bus bars distribute the power to the circuit breakers in an organized manner.
- Define service drop.
A service drop consists of overhead wires and devices that connect the power company power lines to a residence. Service drops are owned and maintained by the service company.
- Describe the NEC standards governing the elevation of service conductors.
To comply with NEC standards, a service head must be at least 10’ above and 3’ to the side of any platform. Service conductors must be at least 3’ from the bottom and sides of the window. Nec standards governing the elevation of service conductors specify a 3’ clearance over adjacent buildings. Sidewalks require a 10’ minimum clearance. Private drives require a 12’ minimum clearance. Alleys and streets require an 18’ minimum clearance.
- Define service lateral.
Is any service to a residence that is achieved by burying the wires underground.
- List the types of service laterals used for residences.
a. From utility manhole in street to service panel disconnect.
b. From utility sidewalk handhole to service panel disconnect.
c. From pole riser to service panel disconnect.
d. From transformer pad to service panel disconnect.
- What is installed when trimming out or finishing a service entrance?
Insultation of service conductors, and branch wires.
- Define generator.
A generator is an electromechanical device that converts mechanical energy into electrical energy by means of electromagnetic induction. AC generators (alternators) convert mechanical energy into AC voltage and current.
- Define main components of an AC generator.
AC generators consist of field windings, an armature, slip rings, and brushes.
- What is the major difference between AC and DC generators?
The major difference between AC and DC generators is that DC generators contain a commutator that reverses the connections to the brushes every half cycle. The commutator maintains a constant polarity of voltage to the load. AC generators use slip rings to connect the armature to the external circuit (load). The slip rings do not reverse the polarity of the output voltage produced by the generator. The result is an alternating sine wave output.
- How are standby generators powered?
Stand by generators are powered by gasoline, natural gas, or LPG.
- How is voltage calculated?
Voltage x Amps = Watts
- Explain how to read an electric meter.
An electric meter has four dials. Each dial has a hand. Electric meters have two dials that read clockwise and two dials that read counterclockwise. To read a meter, always use the number that the hand has just passed (CW or CCW) on each of the dials.
- What is an automatic transfer switch?
An automatic transfer switch is an electrical device that transfers the load of a residence from public utility circuits to the output of a standby generator during a power failure.
