Several items must be decided before you begin planning the wiring. Will you cook with electricity and use an electric oven? What about heating water? What about heating the whole house? This will require special study and will be treated separately later.
If electricity is used solely for lighting, and perhaps for a vacuum cleaner and the usual small appliances, you can get by with a rather simple installation.
Ordinarily in the United States, three-wire, 110-120 volt, 60-cycle, single-phase current is used. This means that three wires are brought to the house from the power lines, the center wire, being the neutral, is always the white wire, and should be placed between the two black wires which carry the current. If you connect either black wire to an electric light or fixture or appliance along with the neutral white wire, you will get 110 volts, but if you connect both the black wires to any piece of equipment you will get 220 volts.
The first step in wiring is to locate the place where the electricity will enter the building. The power company should be consulted, because the pole that looks the best to you may not carry the line you are supposed to be connected to. Find out the exact spot where the wires will leave the pole, and exactly where is the best place to enter the building.
A piece of 11/2" conduit or other appropriate size is put through the roof at the point where the electric wires will enter the building and extended down into the wall to the top of the meter base, and screwed into this meter base. The conduit must extend up through the roof to a point where the wires entering it will be at least 10' off the ground. A weather head is placed at the top of this conduit to permit the wires to enter in such a way that water will not run down into the conduit.
The meter must be on the outside of the building in a place that is easily accessible to the man that reads the meter periodically. Get the required height from your power company. If you can put your main switch and distribution center just below, or near the meter base, it may simplify the wiring problem. It can be put on the inside of the wall if you prefer it to be more protected. A conduit should be run from the meter to the distribution box; sometimes an extra heavy nonmetallic cable is used with good success. Three No. 6 wires should be the absolute minimum size of wiring from the meter to the distribution box. If you have an electric oven and cooking top this should be increased to No. 4 wires or larger. Consult the local building inspector or the power company for information in any particular locality.
When your main switch box is in place, nail all the switch, light, and outlet boxes in place where you want them in the building, including boxes for any special outlets, such as TV, water heating, fan for forced-air furnace, kitchen fan, etc. Then run wires for each circuit from the main box to the outlets, completing one circuit before starting another. You are usually allowed six convenience outlets on one circuit or ten light outlets. It is better not to mix lights and plugs on the same circuit, although it is sometimes permitted in living rooms and bedrooms. The kitchen should have a separate circuit for the plugs, even if you do not use the full number allowed on one circuit. If you have a deep-freeze refrigerator, it might be a good idea to put the clock on the same circuit with it so that any interruption in the electric current to the freezer would be noticed at once.
The principal advantage of having the lights and plugs on different circuits is that if you overload a circuit and "blow" a fuse you will not necessarily be in the dark.
You can use either fuses or circuit breakers in the main distribution box. Fuses are cheaper, but the circuit breakers are easier to put back into service.
The electric stove will require a separate circuit of 220 volts with No. 6 wires running to it, and a 50-ampere circuit breaker or fuse.
An electric water heater will ordinarily be properly served by two No. 10 wires carrying 220 volts.
Two No. 12 wires are usually used on a circuit for convenience outlets, or plugs, as they are often called. Use a 20-ampere fuse.
While lights are often served by No. 14 wires, better service will be given if you also use No. 12 wires for light circuits. It is perfectly permissible to make the wires leading from any one light to a switch of No. 14 wire. Quite commonly a 15-ampere fuse is used in a light circuit.
The entrance switch will have provision for placing the neutral wire in the center, and the black wires one on each side. Then the fuses or circuit breakers will be placed one below the other on each side to make up the branch circuits. Note that the neutral wire is not fused, but each circuit taking off from the black wires is always fused.
Where codes permit, the most satisfactory wiring material for the home builder is the non-metallic cable, which contains either two or three separately insulated conductors and often a bare wire for grounding the outlets and switches. One wire will be white; one will be black; and if there is a third wire it will often be red. The white wire is always the neutral, while the red wire serves the same purpose as a black wire; the color merely keeps one from confusing the circuits.
In wiring the light switches, always switch the hot wire; that is, the black or red wire, never the white or neutral wire. The bare grounding wire is connected to each box as it comes to it, and to a water pipe occasionally to ground the circuits and prevent people from getting a shock from the switches or outlets.
All wires must terminate in metal boxes, and no joints may be made except in these boxes. This eliminates the possibility of a poor joint's being concealed somewhere in the walls with no chance to find it, and makes the wiring safer.
The holes for the wires should be bored near the center of the studs or joists to eliminate the possibility that the lathers might drive a nail into the insulation and short-circuit the wiring. This is especially annoying when a nail joins the stucco wire with a hot wire. The whole house is "hot" and the short is almost impossible to find. Keep the wires where nails will not reach them.
In wiring for convenience outlets or plugs, run two wires from one box to the next, as the fixtures usually have two screws on each side, one for the wires entering the box and one for the wires leaving. Always connect the white wire to the nickel-plated screw and the black wire to the brass-colored screw.
All joints in an electric system should be soldered together and be well taped with plastic tape, or rubber and friction tapes, to prevent short circuits. If wires can be fastened by means of screws that will hold them tightly together, they will not need to be soldered. A loose joint has considerable resistance and will get hot when current runs through it, and it might start a fire; a loose joint will also result in poor service.
Do your wiring with extra care so it will not cause you trouble later on. Good systematic work pays everywhere, but especially in the wiring system.
A three-way switch is very convenient where a room has two doors entering it, and you want to be able to turn on the light from either door as you come into the room. It is fairly easy to install. Run two wires, usually red, from one switch to the other. These wires are called "travelers." Connect these two wires to the proper screws on the switches. These will be two screws that are just alike and at the same end of the switch. Next bring the power to the light and connect the neutral, white, wire to the nickel-plated screw on the light socket. Run the black wire from the main fuse box to one of the switches. Take a black wire from the other switch and connect it to the brass screw on the light socket. Then either switch should operate the light.
It is a good idea to test out the wiring, especially the three-way switches, before the house is lathed, because after the plastering is done, the wiring is pretty well hidden and almost inaccessible. It must be right before it is covered. If the electric company does not connect the wires to the building right away, the test can easily be made by means of a battery. Connect the battery to the wires, one circuit at a time, and use a small buzzer to test the outlets and lights.
A material called B-X, which consists of two or three insulated wires protected also with paper spirally wound with a flexible piece of metal so that the wire is well protected throughout its entire length, is sometimes used for wiring houses. Although some cities do not permit its use, where it is properly installed, it makes a good wiring job. The principal drawback to its use is that the insulation is often injured by the hack saw or other cutting tool so that a short develops between the wire and the metal covering. This can be prevented by extra care in the cutting and by inserting a small, usually red, anti-short bushing in the end of the cable before the wires are connected. The wiring material, of whatever kind, must always be securely fastened to the boxes, to prevent strain on the joints in the wiring.
Where wiring is going to be exposed or where it is enclosed in concrete, blocks, or brickwork, it should be protected by conduit. This is a pipe specially made for the purpose and is similar to water pipe, except that it is smoother inside and comes in 10' lengths. It can be put together with regular plumbers' tools just like water pipe.
A lighter weight pipe, called "E.M.T.," "electrical metallic tubing," or just "steeltube," is often used in place of conduit with equally good results. The principal differences are the greater ease of bending because of the lighter weight, and the connections which instead of being screwed together are made with small connectors and couplings which require no threading of the pipe. The most common size used in houses is 1/2", but a few pieces of 3/4" will be needed where more than four wires go in one direction. Two or three circuits can often run in one conduit to make a neat and simple job. The conduit or steeltube must be securely fastened to each box to make a continuous metal protection for the wires.
Wires are pulled through the conduit by means of a "fish tape." This is a piece of flat steel wire with a loop at the end which is pushed through the conduit from one box to another. The wire is then fastened to the loop and is pulled through the conduit. This makes the wiring continuous from one box to another. Wires should be left projecting from the box about 8" to allow for proper joining of them to each other and to the fixtures.
A person who contemplates doing his own wiring would do well to study a copy of the national electric code to see what is considered good and safe practice in wiring. Wiring is not difficult if one remembers that each circuit must be complete with current going to a fixture in one wire and returning through another wire. The current changes its direction of flow sixty times a second, and provision must always be made for complete circuits. It is important to keep each circuit separate, and to know whether it is 110 or 220 volts. The 220 is used only for stoves and ovens, water heaters, electric clothes dryers, and similar equipment that is permanently connected. Portable equipment and lights are always 110 volts.
In planning your wiring, be sure to put in enough lights so that rooms will be well lighted, and plugs enough so that you will not have to crawl under the furniture to find one. Plugs under windows or near doors will usually be the easiest to get at, while plugs near the corners of the room will often be hidden by furniture. There should be at least three or four plugs in every room, and more in the kitchen and living rooms.
There should be a light over the sink and one over each important working area in the kitchen. A light for each outside door is a good safety measure. Floodlights for the outdoor living area will be found very useful and will not be difficult to put in if they are planned along with the rest of the house. A plug in the garage will be used for vacuum cleaning the car and for small electric hand tools if you do minor repairing at home.
Steps require special illumination to make them safe. A few extra lights, which will not cost much, will be greatly appreciated, and do not be too sparing in the use of three-way switches.
In your wiring, the boxes should be left projecting enough so they will come about even with the surface of the plaster. Care should be taken not to let a box project too much, as it will then be difficult to make the plate fit neatly against the wall.
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