USING ELECTRICITY ABOUT THE HOME 



255 



others. Substances that let the electricity flow easily 

 through them are said to have less resistance than 

 those through which it is harder to flow. 



Whenever electricity flows through a wire it pro- 

 duces some heat, but much more in substances that 

 have high resistance than in those that have low re- 

 sistance. This was clearly shown in your experiment; 

 the iron becomes hot because it has more resistance 

 than the copper. 



Fuses are safety valves for electric currents. When 

 electricity became a common thing around the home 

 for lighting, heating, and running cleaners, people 

 found that oftentimes bare wires in the electric iron 

 or lamp got crossed and allowed large amounts of cur- 

 rent suddenly to flow through them. A short circuit 

 was created, and if the wires were not separated at 

 once so much heat developed that the covering on the 

 wires took fire and burned. This, of course, was dan- 

 gerous, as the wires were frequently placed between 

 the walls. 



The electrical fuse was developed to make a safety 

 valve which would prevent fires. The fuse is a piece of 

 soft metal something like solder which melts at a very 

 low temperature. When a short circuit occurs, the 

 heat developed melts the fuse wire and breaks the 

 electrical pathway before the covering on the wire has 

 had a chance to take fire. 



Fuses are of two common types, plug or screw fuses 

 and cartridge fuses. For home use the plug or screw 

 type is more common, while the cartridge type is used 

 more for industrial purposes where large amounts of 

 current are used. In Figure 404 the construction of the 

 plug type of fuse is shown. The strip of fuse metal 

 F is enclosed in a porcelain plug with a small mica 

 window at W ; the win- 

 dow enables one to tell 

 when the fuse has been 

 burned out and also 

 keeps it enclosed to pre- 

 vent sparks, which fly 

 when the fuse wire 

 melts, from setting any- 

 thing on fire. . 



Figure 404 also 

 shows the construction 

 of the cartridge type of 

 fuse. The strip of fuse 

 metal M is attached through an insulating tube T 

 to the metal ends E. The tube T around the fuse 

 metal is packed with asbestos or some other sub- 

 stance which will immediately quench any spark 

 which forms when the fuse metal melts. 



The diagram, Figure 405, shows where fuses are 

 usually placed in a house wiring plan. When fuses 

 burn out it is a simple matter to replace them. First 



FIG. 404. TWO TYPES OF FUSE 



throw off the main switch which will be found near 

 the fuse box and determine which fuse has been 

 burned by examining the little mica windows of both 

 the circuit fuses and the main fuses. The window 

 of a burned fuse is usually clouded. Remove this fuse 

 and screw in a new one, throw on the main switch, and 

 test by lighting the lights in various parts of the 

 house. Keep extra fuses on hand for emergencies. 



FIG. 405. HOUSE WIRING PLAN 



Never use a makeshift fuse or temporary replacement, 

 as it may cause a fire. 



Exercise. Often, when a fuse burns out in the home, 

 a penny or other metal object is placed behind the burned- 

 out fuse to make the connection previously made by the 

 fuse metal. Suggest the dangers involved in such a prac- 

 tice. 



How do electrical heating devices work? Much of 

 the increase in the use of electrical energy during the 

 past few years has been due to the fact that it may 

 be easily transformed into heat energy with very little 

 loss, and heat energy thus obtained is free of smoke 

 and gases, while coal, oil, and other common fuels 

 are not. Another important fact in the rapid increase 

 in the use of electrical energy for heat is that it may 

 be controlled much more accurately than heat from 

 other sources. 



In the home, heat from electrical energy is used 

 in ranges for cooking and baking, in toasters, elec- 

 tric irons, hot plates, hot pads, heaters, and other 



