Electrical Rewiring

Sample essay topic, essay writing: Electrical Rewiring - 1359 words

The wiring that was installed in a house many years earlier, or even as recently as a decade ago, may not be adequate for the job it is called upon to do today. A complete rewiring job is in order-or is it? Do not jump to the conclusion that every outlet must be torn out and every receptacle replaced. Many times a less expensive job will serve the purpose. Is the wiring inadequate because you are using too many lights? Too many floor lamps? Too many radios and TVs? That is seldom the case. The wiring usually is inadequate because you have added many electrical appliances that were not considered or perhaps were not even on the market at the time of the original wiring job.

The installation does not provide enough circuits to operate a wide assortment of small kitchen appliances, plus range, water heater, clothes dryer, room air conditioners and other heavy appliances. Some of these operate on 240-volt circuits, which may not be available; others operate at 120 volts but when plugged into existing circuits they overload those circuits. In addition, the service entrance equipment may be just too small for the load. To analyze the problem of your particular house, ask yourself this: If you disconnected all the appliances, would you have all the lighting circuits you need? The answer is probably yes, which means that your rewiring job is simplified. You will still have to rewire the house, but probably not as completely as at first appeared necessary

Proceed as if you were starting with a house that had never been wired, but leave the existing lighting circuits intact. (These lighting circuits, of course, will include many receptacles used for small loads like a vacuum cleaner, radio, and TV, but not the receptacles for kitchen or laundry appliances.) There is little difference between old and new work, except that in old work there are a great many problems of carpentry. The problem is to cut an opening where a fixture is to be installed, and another where a switch is to be installed, and then to get the cable inside the wall from one opening to the other with the least amount of work and without tearing up the walls or ceilings more than necessary. One house to be wired may be five years old, another a hundred years old. Different builders use different methods of carpentry.

Every job will be unique. No book can possibly describe all the methods used and all the problems you will meet. Watch buildings while they are being built to get an idea of construction at various points. In old work, good common sense is of more value than many pages of instruction. In general, old work requires more material because it is often wise to use ten extra feet of cable to avoid cutting extra openings in the walls or to avoid cutting timbers. Many problems can be solved without cutting any openings except the ones to be used for outlet boxes and switch boxes.

Others require temporary openings in the wall that must later be repaired. Techniques are given in this chapter for running cable behind walls and ceilings, and for installing boxes, switches, receptacles, and outlets in both lath-and-plaster and drywall construction. All the power you use comes into the building through the service entrance wires and related equipment. Start your planning with a service entrance that will adequately handle present and future needs. Keep in mind that small service wires will not carry a large load satisfactorily.

The service is quite possibly the most important piece of all the rewiring. A building or other structure served shall be supplied by only one service unless permitted. Additional services shall be permitted to supply the following: fire pumps, emergency systems, legally required standby systems, optional standby systems, parallel power production systems. By special permission, additional services shall be permitted for the following. (1) Multiple-occupancy buildings where there is no available space for service equiptment accessible to all occupants, or (2) A single building or other structure sufficiently large to make two or more services necessary.

One building or other structure is not to be supplied through another. Conductors considered to be outside the building are to be bellow 18 inches of dirt or in 2 inches of concrete. Service conductors installed as open cunductors or multiconductor cable without an overall outer jacket shall have a clearence of not less than 3 feet from windows that are designed to be opened, doors, porches, ladders, balconies, stairs, fire escapes, or similar locations. The vertical clearence of final spans above, or within 3 feet measured horizontally of, platforms, projections, or surfaces from which they might be reached. Vegitation such as trees shall not be used as support for any overhead service conductor.

Individual conductors shall be insulated or covered, with one exception, that the grounded conductor of a multi conductor cable shall be permitted to be bare. Conductors shall be sufficient ampacity to carry the curent for the load and shall have adequate mechanical strength. The conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. One exception is that conductors supplying only limited loads of a single branch circuit, such as a small polyphase power, controlled water heaters and similar loads, shall not be smaller than 12 AWG hard-drawn copper or equivalent. Installation and use of all boxes and conduit bodies used as outlet, device, junction, or pull boxes, depending on their use. Round boxes shall not be used where conduits or connectors requiring the use of locknuts or bushings are to be connected to the side of the box. Nonmetalic boxes shall be permitted only with open wiring on insulators, concealed knob-and-tube wiring, cable wiring methods and entirely nonmetalic sheaths, flexible cords, and entirely nonmetalic raceways.

Though there are a couple of exceptions. Where internal bonding means are provided between all entries, nonmetallic boxes shall be permitted to be used with metal racewys or metal-armored cables. All metal boxes shall be grounded. Conduit bodies such as capped elbows and service entrance elbows that enclose conductors 6 AWGor smaller, and are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the conduit body. In damp or wet locations, boxes, conduit bodies, and fittings shall be placed or equipt as to prevent moisture from entering or accumulating within the box, conduit body or fitting.

Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations. The volume of a wiring enclosure (box) shall be the total volume of the assembled sections, and, where used, the space provided by plater rings, dome covers, extension rings, and so forth, that are marked with their volume or are made from boxes the dimensions of wich are listed in NEC Table 314.16(C). Boxes 100 inches cubed or less, and nonmetalic boxes shall be legibly marked by the manufacturer with their volume. In rewiring you must wire for future and present appliances. Appliances shall have no live parts normally exposed to contact other than those parts functioning as open resistance heating elements, such as the heating elements of a toaster, which are necessarely exposed. The rating of an individual branch circuit shall not be less than the marked rating of the appliance.

The branch-circuit rating for an appliance that is continuously loaded, other than a motor operated appliance shall not be less than 125 percent of the marked rating, or not less than 100 percent of the market rating if the branch circuit device and its assembly are listed for continuous loading at 100 percent of its rating. All appliances shall be protected against overcurrent. If a protective device rating is marked on an appliance, the branch circuit overcurrent device rating shall not exceed the protective device rating marked on the appliance. A household-type appliance with surface heating elements having a maximum demand of over 60 amperes shall have its power supply subdivided into two or more circuits, each of which should be provided with overcurrent protection rated at not over 50 amperes.

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