The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Practical Electricity And House Wiring
It is therefore of the utmost importance that when wiring with armored cable, or conduit, the armor of the conduit be fastened to outlet and switch boxes not only securely mechanically, but also so that a good electrical joint also be made, a joint that will carry electricity as well as the wire itself will, should the need for it ever arise. The proper methods of doing this will be covered in the respective chapters devoted to each style of wiring.
Exception to First Paragraph.—In the first paragraph we stated a white wire must run to every outlet. This is true if it is a 115-volt outlet. If the outlet is a 230-volt outlet, for example, a large motor, both wires must be black or some other color, but never white. The white wire always is a grounded wire, and under no circumstances may it be used where it is not grounded.
Fuses, Circuit Breakers And Circuits
Necessity of Fuses.—Many people consider fuses a necessary evil; they blow at the most awkward moments, just when light is needed the most; spares are not always handy. Actually, however, fuses are a most important part of any electrical system.
A ship carries life preservers not because the captain expects it to sink, but as a "safety first" measure. There is a safety valve on the boiler heating your home not because you expect it to burst, but rather to avoid danger in case the pressure does accidentally become too high. So also with fuses: they are the safety valves of an electrical installation, protecting the wiring itself, the electrical devices used on the system, and the people who use the system.
The Principle of a Fuse.—In earlier chapters we discussed the fact that an electric current cannot flow through a wire without causing heat. In any given size of wire the heat created by a current flowing through it is proportional to the square of the amperage; that is, doubling the amperage increases the heat by four times, increasing the amperage to three times the original figure increases the heat nine times, and so on.
If a wire is not properly fused, and then more lamps or other devices are connected to that wire than there should be, consuming more amperes than the wire is capable of carrying safely, the wire might get hot enough to damage its insulation, perhaps hot enough to start a fire. If accidentally two wires are allowed to touch each other causing a short circuit, a definitely dangerous situation exists—a fire will in all likelihood start.
If, however, the wire is properly fused, then when the devices connected to the wire consume more amperes than the wire is capable of carrying safely, the fuse will blow. The installation was protected by the fuse.
