i. Cleat wiring
ii. Wooden casing and capping wiring
iii. CTS or TRS wiring (Batten Wiring System)
iv. Lead sheathed wiring
v. Conduit wiring
vi. Surface or open type
vii. Recessed or concealed type Q # 02: What is cleat wiring? Answer: Cleat wiring is the cheapest method of wiring. The wires remain exposed to view, and these wires are drawn through cleats made of porcelain or plastic or some other approved material. The wires used are either V.I.R. or single-core P.V.C. wires. The cleats are made in two parts, called base and cap. The base is grooved to receive the wire and the cap is placed over it, and the whole of it is placed on a wooden plug which is fixed into the wall. The cleats are tightened up on wooden plugs by means of wooden screws. These cleats are shown in figure below: Q # 03: Give the advantages and disadvantages of cleat wiring? Answer: Following are the advantages and disadvantages of cleat wiring system:
Advantages:
a. It is the cheapest system of internal wiring.
b. Its installation and dismantlement is easy and quick.
c. Material is recoverable after the dismantlement.
d. Inspection, alternations and additions can be easily made.
e. Skill required is little.
Disadvantages:
a. It is not good looking.
b. It is quite temporary and perishes quickly.
c. The wires are exposed to mechanical injury.
d. The insulation catches dampness from the atmosphere and a common salt like substance appears on the insulation which lowers the insulation resistance and causes leakage. Hence, this system of wiring cannot be used in damp places.
e. Oil and smoke are injurious to VIR insulation. Q # 04: What is CTS or TRS Wiring (Batten Wiring System)? Answer: While dealing with cables a kind of cable known as Super-tough Rubber Sheathed cable, has been mentioned. Wiring done with this type of cable is known as C.T.S. Wiring (Cab-Tyre Sheathed Wiring) or T.R.S. Wiring(Tough Rubber-Sheathed Wiring). In practice this type of wiring is adopted only for low voltage circuits.
C.T.S. wiring is used in open space in place of drawing bare conductors. The TRS wiring is suitable for low voltage installations and is extensively used for lighting purposes everywhere i.e. in domestic, commercial or industrial buildings except workshop where it is liable to mechanical injury. This type of wiring is suitable in situations where acids and alkalis are likely to be present. Q # 05: Give the advantages and disadvantages of CTS or TRS Wiring. Answer: Advantages:
i. Its installation is easy and quick and saving in labour largely compensate for the extra cost of the cable.
ii. Its life is long.
iii. Within certain limits it is lire proof.
iv. It can withstand the action of most chemicals such as acids and alkalies.
v. It is cheaper than other types of wiring except cleat wiring.
vi. If the job is carried out with proper attention, it gives a nice appearance.
Disadvantages:
i. Good workmanship is required to make a sound job in TRS wiring. This type of wiring cannot be recommended for use in situations open to sun or rain unless preventive steps are taken to preserve the insulation of cables. Q #06: Isn’t paper a bad thing to insulate with, considering the possibility of fire? Answer: True, but cellulose insulation is treated with borates, which are a Class I fire retardant. Class I refers to ordinary combustibles such as wood and paper, as opposed to Class II combustibles such as flammable liquids, grease, gasoline, oil, etc. Q# 07: What Is loose-fill cellulose Insulation? Answer: There are several different types of cellulose insulation, but the most common type that homeowners will encounter is called loose fill. Pellets of cellulose arc blown into attics or walls (with holes drilled to permit access) and allowed to fill the cavities No pressure is placed on the cellulose, though this is also a method of dense-packing the cellulose that will raise the R-value of the insulation. Q # 08: What is the R-value of cellulose insulation? Answer: On the face of it, cellulose insulation has an R-value of about 3.5 per inch of thickness, compared to fiberglass batt’s R-value between 3 to. 4 per inch. Overall, fiberglass bat more fully covers attic and wall cavities and is denser. So, fiberglass is considered to have an overall better R-value than cellulose insulation. Q # 09: How does cellulose insulation perform against moisture, insects, vermin, etc.? Answer: Fiberglass is better against moisture because it does not absorb water. By contrast, cellulose soaks up moisture and takes a long time—if ever—to dry out. If you have ever owned a down coat or sleeping bag, you know the warnings against getting this insulating material wet: moisture dramatically cuts R-value. Regarding insects and vermin, cellulose insulation does well because of the treatmer3t with borates. Q # 10: How “green” is cellulose insulation? Answer: Pretty green. It uses up to 85% recycled materials, with the remaining 15% made up of the boric treatment. Fiberglass typically is made up of only 30-35% recycled. materials, if even that. Q # 11: How can I decide whether to install cellulose insulation in my walls or attic? Answer: With closed walls, you often have no other choice. Unless you are going through some remodeling where the walls are being opened up, you will need to blow in insulation. For attics, the joists are usually open and accessible to fiberglass batts. However, because of obstructions like wires (and just because of its sheer ease), cellulose insulation is often blown into attics, as well. Q # 12: What is equipment grounding and conductor make-up? Answer: All equipment grounding/bonding conductors must be connected together with solder-less pressure connectors, such as wire nuts or crimp sleeves, leaving sufficient extra conductor for attachment to the metal box and/or device. When crimp type connectors arc used they must be crimped using the tool recommended by the manufacturer. Q # 13: Which cable is generally used for branch circuit wiring? Answer: Type NMB cable (a.k.a. romex) is the most widely used wiring method used in residential dwellings. NM cable must have 90 degree conductor insulation rating which is designated on the cable sheath by a “B”. [334.801 Type N.M.-B, #12, and #14 shall be used for lighting and receptacle circuits, while #10/2 is commonly used for electric water heaters, #10/3 with ground for electrical dryers and cooktops, and #8/3 with ground and #6/3 with ground for ranges and wall mounted ovens. Q .# 14: Give the advantages and disadvantage of conduit wiring. Answer: Following are the advantages and disadvantages
Advantages:
i. It provides protection against mechanical damage.
ii. It provides complete protection against fire due to short circuit etc.
iii. The whole system is water proof.
iv. Replacement and alternation of defective wiring is easy.
v. Its life is long if the work is properly executed and’
vi. It is shock proof also if earthing and bonding is properly done.
Disadvantages:
i. i very costly system of wiring.
ii. Its erection is not so easy and requires time:
iii. Experienced and highly skilled labour is required for carrying out the job.
iv. Internal condensation of moisture may cause damage to the insulation unless the system outlets are properly drained and ventilated. Q # 15: Give the application of conduit wiring. Answer: As this system of wiring provided protection against fire, mechanical damage and dampness so this is the only approved system of wiring for:
i. Places where considerable dust or fluff is present such as in textile mills, saw mills, flour mills etc.
ii. Damp situations.
iii. In workshops for lighting and motor wirings.
iv. Places, where there is possibility of fire hazards such as in oil mills, varnish factories etc.
v. Places, where important documents are kept such as a record room.
vi. Residential and public buildings whet the appearance is the prime thing.
vii. The recessed type conduit wiring is preferred for residential and public buildings. Q # 16: Give the tests of electrical installations before completing. Answer: According to Pakistani Electricity Rules No.47, before completing an installation or an addition to an existing installation is put in to service, the following tests shall be complied with:
As soon as an installation has been completed, or an addition to an existing installation made, a series of tests should be done. In commercial and industrial premises, the installation should also be tested at regular intervals as part of the maintenance programme.
Unfortunately tests are either not done at all or they are inadequate, due to lack of testing equipment. The object of this section is to outline methods of testing with equipment available. Q # 17: What should be the distance between wires in cleat wiring? Answer: Distance Between Wires
For voltages up to 250 volts,, cleats shall be of such dimensions that in the case of branch loads, conductors shall not be less than 2.5 cm apart centre to centre and in the case of sub mains not less than 4 cm apart centre to ‘centre, provided that this shall not apply, if the cable used is twin-core. Care shall be taken in selecting size of cleats particularly for branch distribution wiring where two-way and three-way porcelain cleats are essential, and the difference in size shall be reasonable. Care shall also be taken that grooves of poceIain cleats do not compress the insulation nor be too wide for a very loose fit. Under no circumstances two wires shall be placed in one groove of porcelain cleats. Q # 18: What are the parts of thermal-magnetic miniature circuit breaker? Answer: Thermal-magnetic miniature circuit breaker includes the following component.
1. Actuator lever: used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the “on” position. This is sometimes referred to as “free trip” or “positive trip” operation.
2. Actuator mechanism forces the contacts together or apart.
3. Contacts: Allow current when touching and break the current when moved apart.
4. Terminals
5. Bimetallic strip
6. Calibraüon screw allows the manufacturer to precisely adjust the trip current of the device after assembly.
7. Solenoid
8. Arc divider / extinguisher Q # 19: How insulation resistance between condutctors is tested? Answer: Testing of Insulation Resistance between conductors: For this test use, the circuit of figure which shows that all switches are made on while all the lamps are removed from holders, i.e. such an insulation test, the positive conductor of the circuit is connected to live and the negative conductor is connected to earth terminals respectively shown in figure.
The insulation resistance between the two conductors thus measured with megger should not be less than 50 megohms divided by the number of outlets (points + switch), but need not be more than 1 megohm. If P.V.C. Wires are used the value should be 12 1/2 divide by the if number of outlets. Q # 20: Why is Earthing Necessary? Answer: If the metal parts of an electric machine, appliances of equipment of an electric installation cone in direct contact with bare conductors or current-carrying wires, these metal parts become electrically charged and an inadvertent contact with these parts will give shock to the operating personnel or to persons using it. It is therefore essential from safety point.of4ew to provide arrangement so that the charge of these metal parts may be discharged direct to earth without causing any danger. The safety is ensured only when the metallic frames of machines and apparatus are efficiently connected to earth by means of proper size of earthing conductor. If the resistance of the earth led and the earth electrode is negligible, a large amount of current flows towards the earth as soon as the meal parts come in contact with current-carrying wires. Q # 21: How does Earthing Give Protection? Answer: The usual method of earthing is to join to exposed metal work to earth via, an earth continuity conductor connected to an electrode buried in the earth. In conjunction with a fuse, or other similar device, this then forms a Protective System. Thus if a live conductor accidentally comes into contact with any exposed metal, it is effectively, connected to earth. As long as the overall resistance of the protective system is low, a large faults current flows which blow the fuse. This cuts off the supply and isolates the faulty circuit, preventing risk of shock and fire. Q # 22: Why is Earthing so Important? Answer: Human life is involved where electrical apparatus is used, and an electric shock can be fatal. In addition, a violent short circuit can easily start a disastrous fire on premises. These are well known facts that are often forgotten when electricity is being used every slay. A can be now, tomorrow, live years time, or possible even never. It is because an emergency might never occur that an efficient earthing system is often neither installed nor maintained. Many installations in Pakistan have totally inadequate earthing systems, but this is not realized since a fault has not yet occurred. It is only after someone has been electrocuted or a building is gutted by fire, that it is realized that little or no protection had been given by the protective system. It is obvious that in their own interests, consumers should, insist on an efficient earthing system in the first place, followed by regular testing and thorough maintenance. Q # 23: What should be the distance of earth pit from the building? Answer: Distance of Earth Pit from a Building: The distance of an earth pit from the nearest building shall not be less than 1.5 metres (5 ft). Each and every earth wire shall be connected to an earth electrode. If the phase wire or live wire of a consumer’s circuit comes in contact with a bare conductor, the earthing arrangement shall be such that, the circuit current will rise up to 3 ‘/2 times the rated current of the main fuse or 1 /2 times the setting of the over load earth leakage circuit breaker. As a result the fuse will melt or the circuit breaker will trip. After the completion of earthing arrangement, test shall be carried out to see that the arrangement satisfies this condition otherwise an’ earth leakage circuit breaker is to be installed there. Besides, so long the leakage of current to earth continues, the potential difference between bare conductor and consumer’s earth terminal shall not exceed 40 volts (R.M.S.) Q # 24: Which articles do not need to be Earthed ? Answer: The Articles not to be Earthed
The following articles need not be earthed:
i) Small pieces of metal conduits used to protect small pieces of C.T.S. or P.V.C. wires.
ii) Metal conduit pipes used as wall tubes for the protection of cleat wiring, passing through partition wall.
iii) Metal box covered with non-conducting substance and’ used in connection with C.T’.S or P.V.C wiring.
iv) Lamp caps.
v) Name plate separated by insulating substance, screws and other small substances.
vi) Metal chain (with which .pendant lamp fitting is suspended) not touched with flexible cord of twisted type.
vii) Lamp fitting in a room the floor of which is made of non-conducting substance (the fitting must remain at a height out of reach and away from any earthed body). Q # 25: Give the use of Earth Leakage Circuit Breaker Answer: Use of Earth Leakage Circuit Breaker According to Pakistan Standard it is not necessary to use an earth leakage circuit breaker, at a place where the earth impedance does not exceed 5 ohms with normal soil and 8 ohms with thy and rocky soil. But where the condition of earth is such that this low value of earth impedance is not available and the fuse wire does not melt or the circuit breaker does not fall open before the leakage current uses to a dangerously high value, an earth leakage circuit breaker is to be installed with each earth electrode in a wiring system in order to have effective earthing.
An earth leakage circuit breaker is to be installed keeping in mind the following arrangement for this purpose. Earth leakage circuit breaker (full name is voltage operated earth leakage circuit breaker) should remain connected between consumer’s earth terminal and a suitable earth electrode. Insulated wires must be used for its connection. The electrode with which it is connected must remain outside the resistance area of any other earth electrode, especially where an extra electrode is used for a wiring system.
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