The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Practical Electricity And House Wiring
Two- And Three-Wire Systems
Most homes today are wired for what most people call "110 volts." Actually the voltage is usually 115 volts, frequently 120, and only infrequently 110 volts. However to avoid long clumsy nomenclature, this ordinary voltage regardless of whether in your case it happens to be 110, 115 or 120 volts will be referred to throughout this book, as "115 volts." Since the identical materials are used in wiring, and all appliances* are designed to operate on any of these voltages, the logic of this is apparent.
115-vs. 230 Volts.—In the very first chapter of this book, we found that by dividing the wattage of any device by the voltage, we found the amperage. From this it is evident that any given appliance operating on 115 volts will consume twice the amperes that it will consume at 230 volts. For example, a 1000 watt flatiron will consume about 9 amperes at 115 volts, but only 41/2 at 230 volts. Therefore if we could design all our devices to operate on 230 volts, the total amperage consumed in any house at any given moment would be only half as great as at 115 volts. Therefore, according to Chapter 5, we could cut our wire sizes down by one-half, and reduce our total cost of wiring the house. Fine—but there are many obstacles in the way. Millions of dollars worth of appliances and devices in use on 115 volts cannot be junked. The No. 14 wire used today is about the smallest practical size—smaller sizes would Icink more easily, be more subject to damage in installing. The wire used inside of electrical devices would have to be extremely fine—even on 115-volt devices, wire as fine as a human hair is frequently used.
However, all high-wattage devices which consume a considerable amperage, such as water heaters, large motors, electric ranges, are today usually designed for 230 volts only. An electric range consuming a maximum of 8500 watts would consume at 115 volts about 75 amperes, and would require No. 2 wire; at 230 volts it consumes 371/2 amperes and No. 6 wire is sufficient.
What then do we have to do in a home using both 115 and 230 volt devices—bring in two wires for the 115-volt devices, and another two wires with perhaps a separate main switch, and another meter, for the 230-volt devices? Not at all; we use the 3-wire, 115-230-volt system.
3-Wire System.—To understand this, look at Fig. 69.
