Now the wattage of an incandescent lamp = current x supply voltage. Thus on a final sub-circuit of 5 amp rating, with a 230 volt supply, the maximum number of light points that can be connected.
= Current rating of sub-circuit X Supply voltage/Wattage of lamps to be connected
= 5 x 230/100 = 11.5
In actual practice, not more than 10 incandescent light points should be. supplied by one final sub-circuit, for normal illumination purposes. Q # 03: Give practical advice on wiring as far as numbers of light circuits are concerned. Answer : However small the premises it is recommended that at least two lighting circuits provided. This avoids the whole building being plunged into darkness when a fuse blows. A general guide is that there should be one lighting circuit for every 1000sq.ft of floor area. Switches controlling lights in bathrooms should always be installed outside the bathroom, preferably just outside the bathroom door for convenience.
When flexible cord is used in a lamp pendant, the weight supported by the cord should not be greater than the values given in table at the back of this Manual. The weight should no be taken directly by the cable terminations, but some form of cord clamp should be provided in the lamp holder itself so that the weight is taken by the whole cord. Q # 04: Point out the common mistakes in electrical installations. Answer : One quite common mistake occurs when a lighting extension is required in a factory or commercial building. Two cables are attached temporarily to the nearest switch use on the distribution board and run to their destination. More often this switch-fuse controls a power circuit and the fuses are 15 amp. whereas the cables used to the lighting extension are probably 3/0.29. The mere fact that the fuse rating is larger than the rating of the cable it is supposed to be protecting is not even realized, or if it is, it is ignored.
Actually factory lighting circuit, wired with 7/.029 cables, is protected by 15 amps fuses. If, a pendant consisting of 231.0076 flexible cord is connected to this circuit and a Normal tungsten filament bulb fitted, there is no trouble. It is common for apparatus taking a large current to be connected to the lighting circuit which is not appreciable. Q # 05: What do you mean by circuit diagram of TI? Answer : Circuit diagram j the connections for some common standard florescent lamp circuits. Since there are many makes these diagrams are only meant for guidance, and it is recommended that the manufacture’s wiring diagrams, if available, should be closely followed. Either glow or thermal starters may be fitted. If thermal starters are used, two extra leads are necessary. These connect to the, two springs in the starter socket. Some types of fluorescent lamps have external metal strips and these must be earthed. Q # 06: What is the correct technique to install ceiling fans? Answer : All fans should be suspended on a hook or clamp having double nuts and a double bolt. The size of the clamp rod should not be less than in. thick. The fan must be controlled by a separate switch and must have a speed regulator with an Off position which is capable of reducing the fan speed in steps to at least 40% of full speed. Fans should be hang at a minimum of nine ft. above the floor, and the regulator should be about five ft. above the floor. Q# 07: What is the correct way to wire ceiling fan points? Answer : Fans can be wired on the lighting circuit with 3/.029 cable and supplied from ceiling roses. Not more than about six fans should be connected to any one final subcircuit. For the purpose of estimation of current demand, a fan is assumed to have a wattage rating of 100 watts. Q # 08: Are lights and fans can be wired on one sub circuit? Answer : A combination of lights and fans can be wired on one circuit but the total current taken must not be more than the fuse rating protecting the circuit. Q # 09: If combination of lights and fans are wired on one sub circuit what should be the load consideration of each device. Answer : A fan is assumed to have a power rating of 100 watts and the same power is considered for every incandescent light point. Q # 10: Give the types and current rating of socket outlets available in our country. Answer : Many types of socket outlets are available, the most usual being 2 pin 5 amp, 3 pin 5 amp, and 3 pin 15 amp, all either separately switched or with a switch incorporated. From clad versions of these are also availa1k for industrial use. The shuttered type of sockets is recommended as these provide extra safety especially where children are concerned. Q # 11: How many 5 amp socket outlets should be wired on any one sub-circuit? Answer : Since any sub-circuits having a current rating exceeding 15 amps may only feed one point (I.E.E. Regulation 114), obviously not more than three 5 amp socket outlets should be wired on any one sub-circuit. Also, each 15 amp outlet must be wired on an independent and separate circuit using cables not smaller than 71.029. Q # 12: How many 5 amp socket outlets should be wired on any one sub-circuit? Answer : When connecting up 3 pin sockets to the supply, the red wire (phase conductor) should be connected to the terminal marked “L”, the black wire (neutral conductor) to the terminal marked “N” and the earth wire to the terminal marked “E”.
When conduit is used to socket outlets, the cables used should be either single core V.R.I. or P.V.C. insulated cables. The bare copper earth continuity conductor should in no case be less than 14S.W.G. Q # 13: In what circumstances the use of socket adaptors Is recommended? Answer : The use of socket adaptors is not recommended, especially those designed for 15 A Socket outlets having provision for 5A plugs Inevitably the socket outlets are overloaded, both mechanically and electrically, as shown. The only solution is to install more socket outlets per room. No socket outlet should be fixed in a bathroom and electrical apparatus in bathrooms should be of the fixed type. Q # 14: What do you mean by voltage drop along a cable? Answer : Since every cable has a definite resistance, then there is always a voltage drop along a cable supply current. With short runs of cable, the volt drop is generally negligible, but with long runs of cable of small cross sectional area, the volt drop can become an important factor
The voltage drop from the incoming supply terminals to any point in an installation should not exceed 1+2% of the declared supply voltage (this does not apply to motors). This means that, for a declared supply voltage of say, 250 V, the maximum allowable volt drop is: Q # 15: What are Single and Multi-Core Cables? Answer : The general term “multi-core cable” means a cable with any number of cores over one i.e. twin, three, four core etc. At some time, the question arises whether it is better to use two single core cables instead of a. twin core cable, or three single core cables instead of a three core etc. The choice really depends on: method of installation, degree of protection to cable, ease of installation and cost. Q # 16: What should be the considerations to choice Single or Multi-Core Cables? Answer : If insulated cables are to be run in conduit for protection and the conduit extends for the whole length of circuit run, then it is not really necessary to install and multi-core cable. A circular multi-core cable costs more than the equivalent number of single core cables. For the same conductor size, 3 or 4 single core cables will carry more current than a 3 or 4 core cable when used for three phase AC systems. If cables are to be run in closed ducts in the floor or similar enclosures which afford protection against mechanical damage then circular multi-core cables are not necessary.
If-a cable run is to be on the surface of a Wall or on battens it is always best to run a multi-core cable. Twin and 3 core flat sheathed cables are most suitable for this. The installation is much neater with these flat cables than with a number of single core sheathed cables. Q # 17; Give the types of earth electrode? Answer : The following types of earth electrode are recognized for the purpose of these Regulations:
• Earth rods or pipes,
• Earth tapes or wires,
• Plates,
• Electrodes embedded in foundations.
• Metallic reinforcement of concrete.
• Metallic pipe systems, where not precluded by Regulations 542—14 and 542—15.
• Lead sheaths and other metallic coverings of cables, where not precluded by Regulation 542-15,
• Other suitable underground structures. Q 18: Which voltage grade cable to use? Answer : General wiring cables are manufactured in two voltage grades. A summary of the conditions in which each should be used is listed below.
250/440 V grade cable:
Use with single phase AC supplied of 250 volts and below.
Use with two and three wire DC system where the voltage to earth does not exceed 250 volts or the voltage between conductors does not exceed 440 volts.
Use with a 440 volt AC 3 phase 4 were system having the neutral point solidly earthed either on or very near the premises, and where the load supplied is not large.
660/1100 V grade cable:
Always use with a440 Volt AC, 3 phase 3 wire system. (i.e., having no neutral). Use with a 440 volt AC, 3 phase 4 wire system if the substation is not on the premises or is some distance away, or the load supplied is large Q #19: Why matching the lug terminal size to the cable Size is recommended? Answer : If you use too large a lug terminal, the air pockets or voids in the crimped joint (especially when using coarse stranded wire) will increase voltage resistance. Resistance equals heat, which in turn will lead to a faster rate of corrosion at your terminal end. Never “trim off” strands of wire because the lug terminal you are using is too small to accept your wire. The American Boat and Yacht Council (ABYC) standards state that wiring connections shall be designed and installed to make mechanical and electrical joints without damage to the conductors. Q # 20: Why Rotten to the Core takes place? Answer : The wire that you are terminating must be completely free of corrosion and oxidation: If internally the wire is black or green in color, you must cut back until you find virgin copper, or consider replacing the wire (with tinned wire). The lug terminal must also be free of oxidation. If your spare lugs were stored wet, replace them. The most common problem on a boat is failure of the electrical system. Q #21: What is the crimping technique of cable ligs? Answer : Make sure that the strands of your wire don’t extend too far out the front of the lug and into the terminals eye or spade contact area. When applying pressure with your crimp tool to the lug terminal, make sure that you apply enough pressure so that good I metal-to-metal contact occurs. The goal here, in addition to forming a good mechanical contact, is to break down the oxides that build up on the inside of the terminal lug. Unless a good metal-to-metal contact occurs, the oxides will not be broken down and resistance will build up inside the terminal. Check your crimp by giving the wire a good tug. Q # 22: Is plastic recommended as sleeve of lug terminals? Answer : The best-insulated lug terminals are those with nylon insulator sleeves. Nylon resists UV, gasoline, and oil. Unlike the cheaper vinyl and plastic insulator sleeves, nylon will not punch through or crack and fall apart when the squeeze gets applied. When installing new or replacement equipment, check the lugs supplied by the manufacturer. If they’re not nylon, consider replacing them with a better quality, or plan on- using shrink tubing to dress up the connections post crimp. Q # 23: Is solder not the sole means of mechanical connection in any circuit? Answer : National Marine Electronics Association standards state that solder shall not be the sole means of mechanical connection in any circuit (with the exception of certain-length ship’s battery cables). If inclined to add solder to lug terminal, solder it after you apply the crimp. A good solder joint is bright and shiny. Q # 24: How to wire a power socket? Answer : You can wire an additional electrical outlet on the wall near a computer or entertainment center. Many of the local electrical codes that specie a number of outlets do not account for the multiple power plug needs of a home office, or the expanding number of components attached to stereos and a televisions. A single circuit will deliver power to only a limited number of devices. Put in more outlets for the Q # 25: How can be connected a switch-socket to a spur? Answer : Only one socket outlet can be connected to a spur. (This can be a single or double outlet). Connecting a further outlet is NOT permitted, as this could overload the single cable supplying it. Q # 26: Compare CFL with fluorescent lamps. Answer : Larger fluorescent lamps have been mostly used in commercial or institutional buildings, the compact fluorescent lamp is now available in the same popular sizes as incandescent and is used as an energy-saving alternative in homes. Because they contain mercury, many fluorescent lamps are classified as hazardous waste.
The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal. Q # 27: Compare fluorescent versus incandescent lamps. Answer : Comparing fluorescent versus incandescent lamps, a fluorescent lamp emits mostly ultraviolet (UV) light and a very small amount of visible light, whereas an incandescent lamp produces mostly visible light. And even though UV light can’t be used to “see” anything (unless you want to damage your eyes), a fluorescent lamp is more efficient in producing visible light than an incandescent one - how is this possible?
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